The missing representatives of the hydrated sodium orthophosphate phases: Na3(PO4)(H2O)7 and Na3(PO4)(H2O)6

Weil, M.; Söger, B.

doi:10.1107/S2056989025009843

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ISSN: 2056-9890

Volume 81| Part 12| December 2025| Pages 1119-1125

https://doi.org/10.1107/S2056989025009843

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The missing representatives of the hydrated sodium orthophosphate phases: Na₃(PO₄)(H₂O)₇ and Na₃(PO₄)(H₂O)₆

Matthias Weil ^a ^* and Berthold Söger ^b

^aInstitute for Chemical Technologies and Analytics, Division of Applied Solid State Chemistry, Getreidemarkt 9/E164-05-1, 1060 Vienna, Austria, and ^bX-ray Centre, TU Wien, Getreidemarkt 9/E057-04, 1060 Vienna, Austria
^*Correspondence e-mail: [email protected]

Edited by W. T. A. Harrison, University of Aberdeen, United Kingdom (Received 3 November 2025; accepted 5 November 2025; online 11 November 2025)

The crystal structures of the long-known compound Na₃(PO₄)(H₂O)₆, trisodium orthophosphate hexahydrate, and the compound Na₃(PO₄)(H₂O)₇, trisodium orthophosphate heptahydrate, the possible existence of which is discussed in the literature, were elucidated by single-crystal X-ray diffraction. In both crystal structures, all the water molecules are bound to the sodium cations, but the different water content leads to different arrangements in terms of polyhedral linkage. In the case of the heptahydrate (space group Pca2₁, Z = 4), this results in a layered structure made up from three sixfold coordinated Na⁺ cations with phosphate units in between. In the case of the hexahydrate (space group P1, Z = 4), a three-dimensional network is realised by one fivefold and five sixfold coordinated Na⁺ cations, in which the phosphate units are embedded in the voids. In both crystal structures, the water molecules are involved in complex O—H⋯O hydrogen-bonding networks and form moderately strong hydrogen bonds on average, almost exclusively with the phosphate O atoms. It is noteworthy that some O atoms accept up to five such bonds.

Keywords: crystal structure; orthophosphate; hydrogen bonding; Na₃PO₄ hydrate.

CCDC references: 2500666; 2500667

1. Chemical context

In continuation of our structural studies on M₃(XO₄)(H₂O)_n compounds with tetrahedral anions (M = alkali metal; X = P, V), viz. K₃(PO₄)(D₂O)₇ (Weil & Stöger, 2020 ), K₃(VO₄)(H₂O)_0.56 and K₃(VO₄)(H₂O)₄ (Wolflehner & Weil, 2025 ), we became interested in the Na₃(PO₄)(H₂O)_n system. Trisodium phosphate (TSP) and its hydrated phases are industrially relevant chemicals used on a large scale in the saponification of fats, as cleaning agents, or as water softening agents (Schrödter et al., 2008 ). They are also used as food additives for their properties as complexing agents, acidity regulators, melting salts, emulsifiers or firming agents. Together with other sodium phosphates they are listed under the European approval number E339 for food additives (European Commission, 2025 ). Although TSP and its hydrate phases are well investigated due to these areas of application, there are still contradictions in the literature regarding the existence and composition of some hydrate phases (Menzel & von Sahr, 1937 ; Ingerson & Morey, 1943 ; Quimby, 1947 ; Bell, 1949 ; Wendrow & Kobe, 1952 , 1954 ). For example, a compound with composition ‘Na₃(PO₄)·12H₂O’ is still offered in the chemical trade, even though it has long been known that a phase with this composition does not exist because it contains additional NaOH and must be reformulated as Na₃PO₄·(NaOH)_≃0.25·12H₂O (Tillmanns & Baur, 1970 , 1971 ). Up to now, the existence of the hydrate phases Na₃(PO₄)(H₂O)₈, Na₃(PO₄)(H₂O)₆, and Na₃(PO₄)(H₂O)_0.5 has been unequivocally confirmed (Wendrow & Kobe, 1954), but only the crystal structures of the octahydrate (Larbot & Durand, 1983 ) and the hemihydrate (Averbuch-Pouchot & Durif, 1983 ) have been determined so far. In the older literature, the existence of Na₃(PO₄)(H₂O)₇ has been suggested by some authors (Menzel & von Sahr, 1937; Ingerson & Morey, 1943), but questioned by others (Quimby, 1947; Bell, 1949). In a more recent investigation of the thermal dehydration of ‘Na₃(PO₄)·12H₂O’, the heptahydrate phase of TSP was reported to appear as an intermediate dehydration product as revealed by temperature-dependent Raman studies (Ghule et al., 2001 ).

In this article, we report on the crystal structures of the long-known compound Na₃(PO₄)(H₂O)₆ and of the suspected Na₃(PO₄)(H₂O)₇, thereby confirming the existence of the heptahydrate phase of TSP.

2. Structural commentary

2.1. Na₃(PO₄)(H₂O)₇

Na₃(PO₄)(H₂O)₇ crystallizes in the non-centrosymmetric orthorhombic space group Pca2₁, and the absolute structure of the crystal chosen for data collection has been reliably determined [Flack parameter 0.00 (3)]. The asymmetric unit comprises one formula unit. The crystal structure consists of three Na⁺ cations sixfold surrounded by five water molecules and one phosphate O atom for Na1, and by six water molecules for both Na2 and Na3 (Fig. 1). By sharing edges and corners defined by water molecules, these polyhedra are linked into a layer structure extending parallel to (001), Fig. 2. Thereby, three water molecules (OW3, OW4, OW5) are bound to three Na⁺ cations, and four (OW1, OW2, OW6, OW7) to two Na⁺ cations each (Table 2). The isolated [PO₄]^3– tetrahedra are sandwiched between layers (Table 1 , Fig. 3), with only one of the phosphate oxygen atoms (O1) directly bound to a sodium cation.

Table 1
Selected bond lengths (Å) for Na₃(PO₄)(H₂O)₇

Na1—O1	2.3010 (8)	Na2—O3W	2.4146 (7)
Na1—O1W	2.3146 (7)	Na2—O5W	2.4279 (7)
Na1—O2W	2.3440 (7)	Na2—O4Wⁱ	2.6357 (7)
Na1—O3W	2.4413 (8)	Na3—O4W	2.3605 (7)
Na1—O4Wⁱ	2.4626 (7)	Na3—O7W	2.3606 (7)
Na1—O5Wⁱⁱ	2.5311 (7)	Na3—O2Wⁱⁱⁱ	2.3656 (8)
Na2—O1W	2.2991 (7)	Na3—O3Wⁱⁱⁱ	2.4421 (8)
Na2—O6W	2.3093 (8)	Na3—O5W^iv	2.4439 (7)
Na2—O7W	2.3558 (7)	Na3—O6W^iv	2.6575 (10)
Symmetry codes: (i) ; (ii) $[x+{\script{1\over 2}}, -y+1, z]$ ; (iii) $[x-{\script{1\over 2}}, -y+2, z]$ ; (iv) .

Table 2
Coordination environments in Na₃(PO₄)(H₂O)₇ and Na₃(PO₄)(H₂O)₆, and results of BVS calculations (H atoms not taken into account)

Atom	Number of coordination partners	Polyhedron (idealized point group symmetry; deviation δ from it)	Range of M—O bond lengths (Å)	Average M—O bond length (Å)	Number of water molecules in the first coordination sphere (Na—O < 3.0 Å); number of accepted hydrogen bonds	BVS (v.u.)
Na₃(PO₄)(H₂O)₇
Na1	6	Bailar twist (dynamic) (32; 6.105)	2.3009 (8)–2.5307 (8)	2.399	5	1.19
Na2	6	Bailar twist (dynamic) (32; 7.566)	2.2989 (8)–2.6359 (8)	2.407	6	1.16
Na3	6	Bailar twist (dynamic) (32; 7.357)	2.3604 (8)–2.6575 (10)	2.438	6	1.08
P1	4	tetrahedron ( $[\overline{4}]$ 3m; 1.306)	1.5367 (6)–1.5655 (7)	1.546	–	4.93
O1	2				2	1.50
O2	1				3	1.26
O3	1				3	1.25
O4	1				5	1.17
O1W	2				–	0.47
O2W	2				–	0.43
O3W	3				–	0.53
O4W	3				–	0.48
O5W	3				–	0.49
O6W	2				1	0.36
O7W	2				–	0.43

Na₃(PO₄)(H₂O)₆
Na1	5	Ψ-1 octahedron (4mm; 22.301)	2.3505 (6)–2.5944 (5)	2.418	3	0.98
Na2	6	twisted trigonal prism (32; 6.248)	2.3508 (5)–2.5269 (6)	2.428	6	1.08
Na3	6	twisted trigonal prism (32; 7.483)	2.3549 (5)–2.5365 (6)	2.433	5	1.07
Na4	6	trigonal antifrustum (3m; 12.318)	2.3115 (5)–2.9741 (6)	2.485	5	1.08
Na5	6	twisted trigonal prism (32; 6.907)	2.3151 (5)–2.5838 (6)	2.395	6	1.18
Na6	6	isosceles wedge (mm2; 22.202)	2.3321 (5)–2.9641 (5)	2.533	3	0.96
P1	4	tetrahedron ( $[\overline{4}]$ 3m; 0.995)	1.5336 (5)–1.5525 (5)	1.544	–	4.92
P2	4	tetrahedron ( $[\overline{4}]$ 3m; 0.823)	1.5348 (5)–1.5509 (5)	1.545	–	4.95
O1	3				1	1.69
O2	2				3	1.41
O3	3				2	1.54
O4	3				1	1.70
O5	1				5	1.21
O6	1				3	1.26
O7	1				4	1.22
O8	1				4	1.21
O1W	2				–	0.41
O2W	3				–	0.36
O3W	2				–	0.42
O4W	2				–	0.34
O5W	2				–	0.43
O6W	2				1	0.36
O7W	3				–	0.52
O8W	3				–	0.49
O9W	2				–	0.46
O10W	3				–	0.48
O11W	2				–	0.36
O12W	2				–	0.35

Figure 1
The asymmetric unit of Na₃(PO₄)(H₂O)₇ expanded to show the full coordination environments of the three Na⁺ cations. Displacement ellipsoid are given at the 90% probability level except for H atoms, which are shown with an arbitrary radius. Symmetry codes refer to Table 1

Figure 2
Na₃(PO₄)(H₂O)₇. Linkage of [NaO(H₂O)₅] (Na1) and [Na(H₂O)₆] (Na2, Na3) polyhedra into (001) layers in a view along [00 $[\overline{1}]$ ]. Displacement ellipsoids are as in Fig. 1

. [Symmetry code: (i) x, 1 − y, z.]

Figure 3
Na₃(PO₄)(H₂O)₇. View of the crystal structure along [0 $[\overline{1}]$ 0], showing the [PO₄]^3– tetrahedra in between the cationic layers. Displacement ellipsoids are as in Fig. 1

The description of the closest matching ideal coordination polyhedron for the three Na⁺ sites and quantification of the distortion (δ) from it was performed with the Polynator program (Link & Niewa, 2023 ). In all cases, the idealized coordination polyhedron can be derived from a Bailar twist (dynamic) with moderate distortions (Table 2). The overall mean Na—O bond length in the three [NaO₆] polyhedra amounts to 2.415 Å, in good agreement with the literature value of 2.441 (112) Å averaged from 920 individual polyhedra (Gagné & Hawthorne, 2016 ).

The P—O distances in the orthophosphate group lie in a narrow range (Table 2) with a mean of 1.546 Å, again in good agreement with the literature value of 1.537 (39) Å averaged from 3650 phosphate tetrahedra (Gagné & Hawthorne, 2018 ). The slight angular distortions of the [PO₄]^3– tetrahedron is seen by the variation of the O—P—O angles ranging from 108.28 (3) to 111.12 (4)°.

The crystal structure of Na₃(PO₄)(H₂O)₇ is consolidated by an intricate network of O—H⋯O hydrogen bonds between water molecules as donor groups and phosphate O atoms as acceptor atoms (Table 3, Fig. 4). All the water molecules contribute to the hydrogen bonding with two approximately linear O—H⋯O links. The number of hydrogen bonds accepted differs for the O atoms of the phosphate group. Atom O1, which is the only one additionally bound to Na⁺, is the acceptor of two hydrogen bonds, O2 and O3 are each acceptors of three hydrogen bonds, while O4 is remarkably the acceptor of five hydrogen bonds. The D⋯A distances range from 2.5865 (9) to 3.2041 (11) Å, and on average can be classified as of medium strength (Jeffrey, 1997 ). It is noteworthy that only one hydrogen bond is formed with another water molecule as the acceptor (O6W), namely with the longest observed D⋯A distance (Table 3).

Table 3
Hydrogen-bond geometry (Å, °) for Na₃(PO₄)(H₂O)₇

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1W—H1WA⋯O4^v	0.84 (1)	2.09 (1)	2.9344 (9)	176 (2)
O1W—H1WB⋯O2^iv	0.85 (1)	1.74 (1)	2.5865 (9)	172 (2)
O2W—H2WA⋯O6W^vi	0.85 (1)	2.38 (1)	3.2042 (11)	163 (2)
O2W—H2WB⋯O4^iv	0.84 (1)	1.93 (1)	2.7634 (9)	175 (2)
O3W—H3WA⋯O1^vii	0.85 (1)	1.85 (1)	2.6867 (9)	168 (2)
O3W—H3WB⋯O3^viii	0.87 (1)	1.88 (1)	2.7391 (9)	172 (2)
O4W—H4WA⋯O2^iv	0.84 (1)	1.97 (1)	2.8058 (9)	173 (2)
O4W—H4WB⋯O3^viii	0.86 (1)	1.84 (1)	2.6978 (9)	171 (2)
O5W—H5WA⋯O3^ix	0.85 (1)	1.87 (1)	2.7114 (9)	173 (2)
O5W—H5WB⋯O4^v	0.85 (1)	1.92 (1)	2.7544 (9)	169 (2)
O6W—H6WA⋯O1^ix	0.85 (1)	1.99 (1)	2.8109 (9)	163 (2)
O6W—H6WB⋯O4^vii	0.84 (1)	2.01 (1)	2.8323 (9)	169 (2)
O7W—H7WA⋯O4^viii	0.85 (1)	2.02 (1)	2.8616 (9)	170 (2)
O7W—H7WB⋯O2^ix	0.86 (1)	1.93 (1)	2.7894 (9)	175 (2)
Symmetry codes: (iv) ; (v) $[x-{\script{1\over 2}}, -y+1, z]$ ; (vi) $[-x+{\script{3\over 2}}, y, z-{\script{1\over 2}}]$ ; (vii) $[-x+{\script{3\over 2}}, y, z+{\script{1\over 2}}]$ ; (viii) $[-x+{\script{3\over 2}}, y+1, z+{\script{1\over 2}}]$ ; (ix) $[-x+1, -y+1, z+{\script{1\over 2}}]$ .

Figure 4
Na₃(PO₄)(H₂O)₇. Hydrogen-bonding network (green lines) between water molecules and phosphate tetrahedra. Displacement ellipsoids are as in Fig. 1

2.2. Na₃(PO₄)(H₂O)₆

Na₃(PO₄)(H₂O)₆ crystallizes in the triclinic space group P $[\overline{1}]$ and comprises two formula units in the asymmetric unit. The crystal structure consists of one fivefold coordinated Na⁺ cation (Na1) and five sixfold coordinated Na⁺ cations (Na2–Na6) with different idealized coordination polyhedra (Fig. 5, Tables 2 and 4). The mean Na—O distance of the fivefold coordinated Na⁺ is 2.418 Å, in very good agreement with the literature value of 2.413 (108) Å (Gagné & Hawthorne, 2016). The total mean value of the Na—O distance of the five sixfold-coordinated Na⁺ cations is 2.455 Å, which is slightly longer than in the heptahydrate and corresponds almost perfectly with the value given in the literature (see above).

Table 4
Selected bond lengths (Å) for Na₃(PO₄)(H₂O)₆

Na1—O4	2.3205 (6)	Na4—O1	2.3278 (5)
Na1—O4ⁱ	2.3722 (5)	Na4—O6W	2.3433 (5)
Na1—O4W	2.3907 (6)	Na4—O3Wⁱⁱⁱ	2.3463 (5)
Na1—O2W	2.4107 (6)	Na4—O7W	2.6079 (6)
Na1—O8Wⁱⁱ	2.5944 (5)	Na4—O2W^v	2.9741 (6)
Na2—O5W	2.3508 (5)	Na5—O7W	2.3151 (5)
Na2—O1W	2.3690 (6)	Na5—O9W	2.3155 (5)
Na2—O3W	2.3726 (5)	Na5—O9W^vi	2.3577 (5)
Na2—O1Wⁱⁱⁱ	2.4245 (6)	Na5—O8W	2.3971 (5)
Na2—O12Wⁱⁱⁱ	2.5221 (6)	Na5—O10W	2.4006 (5)
Na2—O4W	2.5269 (6)	Na5—O2W^v	2.5838 (6)
Na3—O5W	2.3549 (5)	Na6—O3	2.3321 (5)
Na3—O1	2.3707 (5)	Na6—O12W	2.3913 (5)
Na3—O8Wⁱⁱ	2.4357 (5)	Na6—O11W	2.4088 (5)
Na3—O11W^iv	2.4372 (5)	Na6—O2^vii	2.4443 (5)
Na3—O7Wⁱⁱ	2.4623 (5)	Na6—O3^vii	2.6552 (6)
Na3—O6W	2.5365 (6)	Na6—O10W	2.9641 (5)
Na4—O10W	2.3115 (5)
Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) .

Figure 5
The asymmetric unit of Na₃(PO₄)(H₂O)₆ expanded to show the full coordination environments of the six Na⁺ cations. Displacement ellipsoid are as in Fig. 1

. Symmetry codes refer to Table 4

The lower water content compared to Na₃(PO₄)(H₂O)₇ can be seen in a lower number of coordinating water molecules for the cations. Overall, only two of the six-coordinated cations (Na2, Na5) have all ligand atoms from water molecules, two cations (Na3, Na4) have five water molecules and one phosphate O atom in the coordination sphere, and one (Na6) has only three water molecules and three phosphate O atoms; the five-coordinated Na1 also has three water molecules as direct coordination partners. The individual polyhedra are in turn connected to each other by sharing corners and edges, with four of the water molecules (O2W, O7W, O8W, O10W) bound to three cations simultaneously and the rest bound to two (Table 2).

Another difference to Na₃(PO₄)(H₂O)₇ concerns the resulting linkage of these polyhedra, which in this case is not in the form of layers but as a three-dimensional framework structure (Fig. 6). The [PO₄]^3– tetrahedra are isolated and located in the voids of this arrangement (Fig. 7). It is noteworthy here that the two unique [PO₄]^3– tetrahedra exhibit different properties. While all the O atoms of one tetrahedron (P1) are also shared with Na⁺ cations, the O atoms of the other tetrahedron (P2) belong exclusively to the P atom. However, these differences are not noticeable in the P—O bond lengths (Table 2). The range of P—O bond lengths is approximately the same in both phosphate tetrahedra, and the respective mean values correspond to the literature value (see above). The range of O—P—O angles also does not differ significantly, ranging from 107.68 (3) to 110.03 (2)° for P1 and from 108.71 (3) to 110.23 (2)° for P2.

Figure 6
Na₃(PO₄)(H₂O)₆. Linkage of [NaO₂(H₂O)₃] (Na1), [Na(H₂O)₆] (Na2, Na5), [NaO(H₂O)₅] (Na3, Na4), and [NaO₃(H₂O)₃] (Na6) polyhedra into a framework structure in a view along [0 $[\overline{1}]$ 0]. Displacement ellipsoids are as in Fig. 1

. [Symmetry code: (i) 1 − x, y, z.]

Figure 7
Na₃(PO₄)(H₂O)₆. View of the crystal structure along [ $[\overline{1}]$ 00] showing the [PO₄]^3– tetrahedra in the voids of the cationic framework. Displacement ellipsoids are as in Fig. 1

A network of O—H⋯O hydrogen bonds consolidates the crystal structure of the hexahydrate and exhibit similar D⋯A distances and angles (Table 5, Fig. 8) as the heptahydrate. With only one water molecule as an additional acceptor (O6W), the phosphate O atoms primarily assume this role in the hexahydrate as well. The differences between the two phosphate groups are clearly evident in the hydrogen-bonding network. The total number of accepted hydrogen bonds of seven for the P1 phosphate tetrahedron (which also bonds to sodium ions) is significantly lower than for the ‘free' P2 tetrahedron with 15.

Table 5
Hydrogen-bond geometry (Å, °) for Na₃(PO₄)(H₂O)₆

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1W—H1WA⋯O1	0.85 (1)	1.83 (1)	2.6704 (7)	171 (1)
O1W—H1WB⋯O5^viii	0.86 (1)	2.09 (1)	2.9417 (6)	172 (1)
O2W—H2WA⋯O6W^ix	0.82 (1)	2.47 (1)	3.1079 (8)	136 (1)
O2W—H2WB⋯O5^viii	0.82 (1)	2.03 (1)	2.8343 (7)	167 (1)
O3W—H3WA⋯O8^x	0.83 (1)	1.84 (1)	2.6651 (6)	175 (1)
O3W—H3WB⋯O8^viii	0.85 (1)	2.03 (1)	2.8469 (6)	161 (1)
O4W—H4WA⋯O7	0.82 (1)	2.04 (1)	2.8552 (6)	173 (1)
O4W—H4WB⋯O8^x	0.81 (1)	2.00 (1)	2.7987 (7)	170 (1)
O5W—H5WA⋯O6	0.84 (1)	1.80 (1)	2.6359 (7)	172 (1)
O5W—H5WB⋯O5^xi	0.83 (1)	2.43 (1)	3.2184 (7)	159 (1)
O6W—H6WA⋯O8^xi	0.84 (1)	1.95 (1)	2.7557 (6)	159 (1)
O6W—H6WB⋯O2ⁱⁱ	0.84 (1)	1.84 (1)	2.6508 (6)	160 (1)
O7W—H7WA⋯O2	0.86 (1)	1.77 (1)	2.6209 (6)	172 (1)
O7W—H7WB⋯O2ⁱⁱ	0.85 (1)	2.12 (1)	2.9658 (6)	174 (1)
O8W—H8WA⋯O7ⁱⁱ	0.83 (1)	1.95 (1)	2.7783 (7)	172 (1)
O8W—H8WB⋯O4^v	0.84 (1)	1.81 (1)	2.6220 (6)	164 (1)
O9W—H9WA⋯O5^xii	0.82 (1)	1.93 (1)	2.7531 (7)	174 (1)
O9W—H9WB⋯O3^v	0.84 (1)	1.90 (1)	2.7235 (6)	167 (1)
O10W—H10A⋯O7^xii	0.83 (1)	1.91 (1)	2.7345 (6)	175 (1)
O10W—H10B⋯O3^vii	0.85 (1)	1.85 (1)	2.6902 (6)	171 (1)
O11W—H11A⋯O6ⁱⁱⁱ	0.87 (1)	1.90 (1)	2.7666 (6)	173 (1)
O11W—H11B⋯O5^viii	0.85 (1)	2.00 (1)	2.8460 (7)	176 (1)
O12W—H12A⋯O6ⁱⁱⁱ	0.86 (1)	1.90 (1)	2.7438 (7)	168 (1)
O12W—H12B⋯O7^xii	0.85 (1)	1.97 (1)	2.8165 (6)	171 (1)
Symmetry codes: (ii) ; (iii) ; (v) ; (vii) ; (viii) ; (ix) ; (x) ; (xi) ; (xii) .

Figure 8
Na₃(PO₄)(H₂O)₆. Hydrogen-bonding network (green lines) between water molecules and phosphate tetrahedra. Displacement ellipsoids are as in Fig. 1

2.3. Bond valence sum calculation

Calculations of bond-valence sums (BVS; Brown, 2002 ) were performed with the program ECoN21 (Ilinca, 2022 ) without contributions of H atoms. The BVS values of all atomic sites are listed in Table 2 and correspond to expectations for Na (1.0 valence unit, v. u.) and for P (5.0 v. u.). The BVS values obtained for the O atoms reflect their roles in the hydrogen-bonding networks. All water O atoms (O*W) have a value of less than 0.5 v.u., and all phosphate O atoms have a value significantly below the expected BVS value of 2.0 v.u., which is due to their role as acceptors of hydrogen bonds. There is a consistent trend for these phosphate O atoms showing that the BVS value decreases as the number of accepted hydrogen bonds increases (Tables 2, 3 and 5).

3. Database survey

A search of the Inorganic Crystal Structure Database (ICSD; data release 2025-1; Zagorac et al., 2019 ) for Na₃(XO₄)(H₂O)_n phases with tetrahedral (XO₄)^3– anions (X = P, As, V) revealed two entries for orthophosphates, Na₃(PO₄)(H₂O)₈ (Larbot & Durand, 1983) and Na₃(PO₄)(H₂O)_0.5 (Averbuch-Pouchot & Durif, 1983), no entry for orthoarsenates, and one entry for orthovanadates, Na₃(VO₄)(H₂O)₃ (Kato & Takayama-Muromachi, 1987 ).

Na₃(PO₄)(H₂O)₈ (space group P $[\overline{1}]$ ) comprises two formula units in the asymmetric unit. From the six octahedrally surrounded Na⁺ cations, five exhibit solely water molecules in the coordination sphere, and one four water molecules and two O atoms from phosphate groups. Like in Na₃(PO₄)(H₂O)₇, the polyhedra around the Na⁺ cations are linked into a layered arrangement, with [PO₄]^3– groups situated in between. Hydrogen atoms have not been determined for this structure, hence details on hydrogen-bonding interactions are limited to D⋯A distances.

Na₃(PO₄)(H₂O)_0.5 (space group C2/c) comprises one formula unit in the asymmetric unit. One of the three octahedrally surrounded Na⁺ cations has solely phosphate O atoms in the coordination sphere, while the other two have one water molecule and five phosphate O atoms as ligands. Linking these polyhedra leads a framework structure. The water molecule is situated on a twofold rotation axis and is the donor of two symmetry-related hydrogen bonds of medium strength.

Na₃(VO₄)(H₂O)₃ (space group R3) comprises one third of the formula unit in the asymmetric unit, with the V and one O atom situated on a threefold rotation axis. The [NaO₃(H₂O)₃] octahedron shares its edges with neighbouring octahedra to form a framework structure. In this structure, too, two hydrogen bonds of medium strength are formed by the water molecule.

4. Synthesis and crystallization

For the crystal growth of Na₃(PO₄)(H₂O)₇, a concentrated aqueous solution of Na₃(PO₄) was prepared in a polypropylene beaker from commercially available Na₃(PO₄)(H₂O)₆ (Budenheim KG, Germany) and evaporated for one day at 361 K in a drying oven. Pieces were broken off from the compact product and crushed again by gentle pressing between two glass slides. Crystals were isolated under a polarizing microscope and tested on a single crystal diffractometer. Besides weakly diffracting multi-domain crystals of undetermined composition, high-quality crystals of Na₃(PO₄)(H₂O)₇ were obtained this way.

A suitable single crystals of Na₃(PO₄)(H₂O)₆ was taken directly from the storage container of a commercially available sample (Budenheim KG, Germany).

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 6. To prevent possible water release, data collections were performed at 100 K. Experience has shown that measurements at low temperatures also enable better localization of hydrogen atom positions from difference-Fourier maps, which was the case for all hydrogen atoms in both hydrate phases. Their O—H bond lengths were refined with restraints using a value of 0.85 (1) Å. Quick measurements of crystals of both compounds at room temperature showed no notable differences from the low-temperature measurements.

Table 6
Experimental details

	Na₃(PO₄)(H₂O)₇	Na₃(PO₄)(H₂O)₆
Crystal data
M_r	290.05	272.04
Crystal system, space group	Orthorhombic, Pca2₁	Triclinic, P $[\overline{1}]$
Temperature (K)	100	100
a, b, c (Å)	12.3169 (7), 6.5324 (3), 12.6602 (7)	9.5490 (4), 9.6353 (5), 12.1401 (6)
α, β, γ (°)	90, 90, 90	109.289 (4), 101.228 (4), 108.476 (4)
V (Å³)	1018.63 (9)	942.35 (8)
Z	4	4
Radiation type	Mo Kα	Mo Kα
μ (mm⁻¹)	0.44	0.46
Crystal size (mm)	0.28 × 0.19 × 0.10	0.13 × 0.09 × 0.04

Data collection
Diffractometer	Bruker APEXII CCD	Stoe STADIVARI
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )	Multi-scan (LANA; Koziskova et al., 2016 )
T_min, T_max	0.695, 0.748	0.911, 0.991
No. of measured, independent and observed [I > 2σ(I)] reflections	44325, 6462, 6108	42672, 9215, 8427
R_int	0.032	0.018

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.020, 0.046, 1.07	0.020, 0.056, 1.06
No. of reflections	6462	9215
No. of parameters	192	325
No. of restraints	15	24
H-atom treatment	All H-atom parameters refined	Only H-atom coordinates refined
Δρ_max, Δρ_min (e Å⁻³)	0.32, −0.22	0.53, −0.32
Absolute structure	Flack x determined using 2767 quotients [(I⁺)−(I⁻)]/[(I⁺)+(I⁻)] (Parsons et al., 2013 )	–
Absolute structure parameter	0.00 (3)	–
Computer programs: APEX3 and SAINT (Bruker, 2021 ), X-AREA (Stoe, 2024 ), SHELXT (Sheldrick, 2015a ), SHELXL (Sheldrick, 2015b ), ATOMS (Dowty, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC references: 2500666; 2500667

Crystal structure: contains datablocks Na3PO4H2O6, Na3PO4H2O7, global. DOI: https://doi.org/10.1107/S2056989025009843/hb8171sup1.cif

Structure factors: contains datablock Na3PO4H2O6. DOI: https://doi.org/10.1107/S2056989025009843/hb8171Na3PO4H2O6sup2.hkl

Structure factors: contains datablock Na3PO4H2O7. DOI: https://doi.org/10.1107/S2056989025009843/hb8171Na3PO4H2O7sup3.hkl

checkCIF report

Computing details top

Trisodium orthophosphate hexahydrate (Na3PO4H2O6) top

Crystal data top

Na₃(PO₄)(H₂O)₆	Z = 4
M_r = 272.04	F(000) = 560
Triclinic, P1	D_x = 1.917 Mg m⁻³
a = 9.5490 (4) Å	Mo Kα radiation, λ = 0.71073 Å
b = 9.6353 (5) Å	Cell parameters from 42515 reflections
c = 12.1401 (6) Å	θ = 1.9–36.7°
α = 109.289 (4)°	µ = 0.46 mm⁻¹
β = 101.228 (4)°	T = 100 K
γ = 108.476 (4)°	Plate, colourless
V = 942.35 (8) Å³	0.13 × 0.09 × 0.04 mm

Data collection top

Stoe STADIVARI diffractometer	9215 independent reflections
Radiation source: Axo_Mo	8427 reflections with I > 2σ(I)
Graded multilayer mirror monochromator	R_int = 0.018
Detector resolution: 13.33 pixels mm^-1	θ_max = 36.9°, θ_min = 2.4°
rotation method, ω scans	h = −16→13
Absorption correction: multi-scan (LANA; Koziskova et al., 2016)	k = −10→16
T_min = 0.911, T_max = 0.991	l = −20→20
42672 measured reflections

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.020	Only H-atom coordinates refined
wR(F²) = 0.056	w = 1/[σ²(F_o²) + (0.0291P)² + 0.1762P] where P = (F_o² + 2F_c²)/3
S = 1.06	(Δ/σ)_max = 0.002
9215 reflections	Δρ_max = 0.53 e Å⁻³
325 parameters	Δρ_min = −0.32 e Å⁻³
24 restraints

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Na1	0.46040 (3)	−0.10173 (3)	0.34021 (2)	0.01131 (5)
Na2	0.35186 (3)	−0.16635 (3)	−0.00188 (2)	0.00949 (5)
Na3	0.31635 (3)	0.17465 (3)	0.28593 (2)	0.00889 (4)
Na4	0.63254 (3)	0.45792 (3)	0.28635 (2)	0.01083 (5)
Na5	0.81993 (3)	0.85412 (3)	0.47425 (2)	0.00871 (4)
Na6	1.01416 (3)	0.39929 (3)	0.34657 (2)	0.00953 (5)
P1	0.69885 (2)	0.28053 (2)	0.46564 (2)	0.00492 (3)
P2	−0.13497 (2)	−0.26690 (2)	0.07362 (2)	0.00497 (3)
O1	0.58849 (5)	0.23882 (5)	0.33732 (4)	0.00922 (7)
O2	0.70340 (5)	0.43730 (5)	0.56120 (4)	0.00895 (7)
O3	0.86741 (5)	0.31380 (5)	0.46279 (4)	0.00820 (7)
O4	0.63891 (5)	0.14101 (5)	0.50280 (4)	0.00914 (7)
O5	−0.18726 (5)	−0.13720 (5)	0.14385 (4)	0.00937 (7)
O6	−0.04459 (5)	−0.20890 (5)	−0.00562 (4)	0.00942 (7)
O7	−0.03024 (5)	−0.30105 (5)	0.16635 (4)	0.00814 (7)
O8	−0.28289 (5)	−0.42346 (5)	−0.01384 (4)	0.00825 (7)
O1W	0.60359 (5)	0.02983 (6)	0.13572 (4)	0.01135 (7)
H1WA	0.6072 (14)	0.0949 (13)	0.2043 (10)	0.017*
H1WB	0.6714 (13)	−0.0106 (14)	0.1449 (11)	0.017*
O2W	0.60598 (6)	−0.25279 (6)	0.26337 (5)	0.01358 (8)
H2WA	0.5326 (13)	−0.3403 (13)	0.2176 (11)	0.020*
H2WB	0.6559 (14)	−0.2320 (15)	0.2186 (11)	0.020*
O3W	0.43736 (5)	−0.37555 (5)	−0.07135 (4)	0.00970 (7)
H3WA	0.3845 (13)	−0.4408 (13)	−0.0491 (10)	0.015*
H3WB	0.5313 (12)	−0.3654 (13)	−0.0451 (10)	0.015*
O4W	0.26544 (5)	−0.28566 (6)	0.14281 (4)	0.01040 (7)
H4WA	0.1781 (12)	−0.2915 (14)	0.1430 (10)	0.016*
H4WB	0.2588 (13)	−0.3752 (13)	0.1040 (10)	0.016*
O5W	0.24137 (5)	0.01652 (5)	0.07208 (4)	0.01034 (7)
H5WA	0.1484 (12)	−0.0496 (13)	0.0527 (10)	0.016*
H5WB	0.2323 (13)	0.0709 (13)	0.0327 (10)	0.016*
O6W	0.37090 (5)	0.42450 (6)	0.24429 (4)	0.01154 (8)
H6WA	0.3214 (13)	0.4155 (14)	0.1753 (10)	0.017*
H6WB	0.3349 (13)	0.4744 (14)	0.2944 (10)	0.017*
O7W	0.63802 (5)	0.65073 (5)	0.49826 (4)	0.00930 (7)
H7WA	0.6496 (13)	0.5753 (13)	0.5170 (10)	0.014*
H7WB	0.5398 (12)	0.6220 (13)	0.4755 (10)	0.014*
O8W	0.77912 (5)	1.03439 (5)	0.64277 (4)	0.00946 (7)
H8WA	0.8590 (12)	1.1091 (13)	0.6996 (10)	0.014*
H8WB	0.7518 (13)	1.0782 (13)	0.5982 (10)	0.014*
O9W	0.91801 (5)	1.03959 (5)	0.39645 (4)	0.00958 (7)
H9WA	0.8919 (13)	0.9917 (13)	0.3208 (9)	0.014*
H9WB	0.8890 (13)	1.1149 (13)	0.4071 (10)	0.014*
O10W	0.88846 (5)	0.64630 (6)	0.35754 (4)	0.00997 (7)
H10A	0.9146 (13)	0.6684 (13)	0.3019 (10)	0.015*
H10B	0.9719 (12)	0.6652 (13)	0.4111 (10)	0.015*
O11W	1.05705 (5)	0.17297 (5)	0.22373 (4)	0.00941 (7)
H11A	1.0618 (13)	0.1875 (13)	0.1572 (10)	0.014*
H11B	0.9869 (12)	0.0787 (12)	0.1988 (10)	0.014*
O12W	0.91400 (6)	0.38437 (6)	0.14452 (4)	0.01083 (7)
H12A	0.9607 (13)	0.3419 (13)	0.0989 (10)	0.016*
H12B	0.9286 (13)	0.4756 (12)	0.1426 (11)	0.016*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Na1	0.00846 (10)	0.01261 (11)	0.00943 (11)	0.00320 (9)	0.00247 (8)	0.00208 (9)
Na2	0.00993 (10)	0.00898 (10)	0.00958 (10)	0.00441 (8)	0.00319 (8)	0.00350 (8)
Na3	0.00822 (10)	0.00915 (10)	0.00819 (10)	0.00328 (8)	0.00196 (8)	0.00311 (8)
Na4	0.00839 (10)	0.01256 (11)	0.00898 (10)	0.00200 (9)	0.00190 (8)	0.00434 (9)
Na5	0.00863 (10)	0.00774 (10)	0.00979 (10)	0.00296 (8)	0.00392 (8)	0.00363 (8)
Na6	0.00947 (10)	0.00953 (10)	0.00881 (10)	0.00287 (8)	0.00378 (8)	0.00354 (8)
P1	0.00444 (5)	0.00515 (5)	0.00481 (5)	0.00190 (4)	0.00119 (4)	0.00196 (4)
P2	0.00499 (5)	0.00510 (5)	0.00470 (5)	0.00206 (4)	0.00134 (4)	0.00208 (4)
O1	0.00815 (16)	0.01242 (18)	0.00564 (15)	0.00500 (14)	0.00015 (13)	0.00263 (14)
O2	0.01142 (17)	0.00766 (16)	0.00709 (16)	0.00488 (14)	0.00300 (13)	0.00145 (13)
O3	0.00551 (14)	0.01020 (16)	0.01047 (17)	0.00352 (13)	0.00329 (13)	0.00557 (14)
O4	0.00861 (16)	0.00780 (16)	0.01155 (17)	0.00204 (13)	0.00348 (14)	0.00591 (14)
O5	0.00990 (16)	0.00825 (16)	0.00981 (17)	0.00520 (14)	0.00346 (14)	0.00214 (14)
O6	0.00998 (16)	0.01025 (17)	0.00833 (16)	0.00251 (14)	0.00420 (13)	0.00521 (14)
O7	0.00774 (15)	0.00951 (16)	0.00773 (16)	0.00397 (13)	0.00111 (13)	0.00471 (14)
O8	0.00684 (15)	0.00686 (15)	0.00772 (16)	0.00093 (13)	0.00056 (13)	0.00209 (13)
O1W	0.01197 (18)	0.01287 (18)	0.00871 (17)	0.00664 (15)	0.00221 (14)	0.00321 (15)
O2W	0.00987 (17)	0.0143 (2)	0.0168 (2)	0.00397 (15)	0.00499 (16)	0.00754 (17)
O3W	0.00861 (16)	0.01147 (18)	0.01137 (17)	0.00478 (14)	0.00439 (14)	0.00633 (15)
O4W	0.00843 (16)	0.00966 (17)	0.01095 (17)	0.00372 (14)	0.00291 (14)	0.00203 (14)
O5W	0.00952 (16)	0.00937 (17)	0.01091 (17)	0.00374 (14)	0.00255 (14)	0.00350 (14)
O6W	0.01125 (17)	0.0173 (2)	0.00671 (16)	0.00813 (16)	0.00269 (14)	0.00377 (15)
O7W	0.00787 (16)	0.00895 (16)	0.01092 (17)	0.00252 (13)	0.00286 (13)	0.00505 (14)
O8W	0.00934 (16)	0.00804 (16)	0.00966 (17)	0.00319 (14)	0.00179 (14)	0.00334 (14)
O9W	0.01174 (17)	0.00927 (17)	0.00822 (17)	0.00525 (14)	0.00296 (14)	0.00359 (14)
O10W	0.00814 (16)	0.01246 (18)	0.00823 (16)	0.00333 (14)	0.00267 (13)	0.00402 (14)
O11W	0.01033 (16)	0.00900 (17)	0.00891 (16)	0.00350 (14)	0.00338 (14)	0.00413 (14)
O12W	0.01409 (18)	0.00960 (17)	0.01098 (18)	0.00646 (15)	0.00509 (15)	0.00482 (14)

Geometric parameters (Å, º) top

Na1—O4	2.3205 (6)	Na4—O2W^v	2.9741 (6)
Na1—O4ⁱ	2.3722 (5)	Na5—O7W	2.3151 (5)
Na1—O4W	2.3907 (6)	Na5—O9W	2.3155 (5)
Na1—O2W	2.4107 (6)	Na5—O9W^vi	2.3577 (5)
Na1—O8Wⁱⁱ	2.5944 (5)	Na5—O8W	2.3971 (5)
Na2—O5W	2.3508 (5)	Na5—O10W	2.4006 (5)
Na2—O1W	2.3690 (6)	Na5—O2W^v	2.5838 (6)
Na2—O3W	2.3726 (5)	Na6—O3	2.3321 (5)
Na2—O1Wⁱⁱⁱ	2.4245 (6)	Na6—O12W	2.3913 (5)
Na2—O12Wⁱⁱⁱ	2.5221 (6)	Na6—O11W	2.4088 (5)
Na2—O4W	2.5269 (6)	Na6—O2^vii	2.4443 (5)
Na3—O5W	2.3549 (5)	Na6—O3^vii	2.6552 (6)
Na3—O1	2.3707 (5)	Na6—O10W	2.9641 (5)
Na3—O8Wⁱⁱ	2.4357 (5)	P1—O4	1.5336 (5)
Na3—O11W^iv	2.4372 (5)	P1—O1	1.5419 (4)
Na3—O7Wⁱⁱ	2.4623 (5)	P1—O3	1.5482 (4)
Na3—O6W	2.5365 (6)	P1—O2	1.5525 (5)
Na4—O10W	2.3115 (5)	P2—O6	1.5348 (5)
Na4—O1	2.3278 (5)	P2—O7	1.5462 (4)
Na4—O6W	2.3433 (5)	P2—O5	1.5476 (4)
Na4—O3Wⁱⁱⁱ	2.3463 (5)	P2—O8	1.5509 (5)
Na4—O7W	2.6079 (6)

O1—P1—O2	108.70 (2)	P1—O2—Na6^vii	100.64 (2)
O1—P1—O3	110.03 (2)	P1—O3—Na6	136.44 (3)
O3—P1—O2	107.68 (3)	P1—O3—Na6^vii	92.37 (2)
O4—P1—O1	109.62 (3)	Na6—O3—Na6^vii	95.452 (17)
O4—P1—O2	110.25 (3)	P1—O4—Na1ⁱ	136.46 (3)
O4—P1—O3	110.52 (2)	P1—O4—Na1	114.59 (3)
O5—P2—O8	108.71 (2)	Na1—O4—Na1ⁱ	97.030 (18)
O6—P2—O5	109.77 (3)	Na2—O1W—Na2ⁱⁱⁱ	94.480 (19)
O6—P2—O7	109.83 (2)	Na2—O1W—H1WA	116.4 (8)
O6—P2—O8	108.30 (2)	Na2ⁱⁱⁱ—O1W—H1WA	109.8 (8)
O7—P2—O5	110.23 (2)	Na2ⁱⁱⁱ—O1W—H1WB	109.4 (8)
O7—P2—O8	109.96 (2)	Na2—O1W—H1WB	113.0 (8)
O4—Na1—O4ⁱ	82.970 (18)	H1WA—O1W—H1WB	112.2 (11)
O4—Na1—O2W	107.43 (2)	Na1—O2W—Na4^viii	131.39 (2)
O4ⁱ—Na1—O2W	118.22 (2)	Na1—O2W—Na5^viii	96.15 (2)
O4—Na1—O4W	159.42 (2)	Na1—O2W—H2WA	99.2 (8)
O4ⁱ—Na1—O4W	108.745 (19)	Na1—O2W—H2WB	121.8 (8)
O4—Na1—O8Wⁱⁱ	93.816 (18)	Na4^viii—O2W—H2WA	63.3 (8)
O4ⁱ—Na1—O8Wⁱⁱ	63.542 (16)	Na4^viii—O2W—H2WB	106.7 (8)
O4W—Na1—O2W	82.410 (19)	Na5^viii—O2W—Na4^viii	74.081 (16)
O4W—Na1—O8Wⁱⁱ	77.394 (17)	Na5^viii—O2W—H2WA	134.0 (8)
O1W—Na2—O1Wⁱⁱⁱ	85.520 (19)	Na5^viii—O2W—H2WB	103.7 (9)
O1W—Na2—O3W	94.509 (18)	H2WA—O2W—H2WB	104.3 (12)
O1Wⁱⁱⁱ—Na2—O4W	168.587 (19)	Na2—O3W—H3WA	100.2 (8)
O1W—Na2—O4W	98.343 (18)	Na2—O3W—H3WB	124.6 (7)
O1Wⁱⁱⁱ—Na2—O12Wⁱⁱⁱ	96.788 (18)	Na4ⁱⁱⁱ—O3W—Na2	104.369 (19)
O1W—Na2—O12Wⁱⁱⁱ	177.322 (19)	Na4ⁱⁱⁱ—O3W—H3WA	115.0 (8)
O3W—Na2—O1Wⁱⁱⁱ	103.980 (19)	Na4ⁱⁱⁱ—O3W—H3WB	107.3 (8)
O3W—Na2—O12Wⁱⁱⁱ	83.629 (18)	H3WA—O3W—H3WB	105.8 (11)
O5W—Na2—O1Wⁱⁱⁱ	82.339 (18)	Na1—O4W—Na2	103.47 (2)
O5W—Na2—O1W	90.266 (19)	Na1—O4W—H4WA	111.4 (8)
O5W—Na2—O3W	172.34 (2)	Na1—O4W—H4WB	123.6 (8)
O5W—Na2—O4W	86.890 (18)	Na2—O4W—H4WA	111.5 (8)
O5W—Na2—O12Wⁱⁱⁱ	91.388 (18)	Na2—O4W—H4WB	96.6 (8)
O1—Na3—O6W	87.697 (18)	H4WA—O4W—H4WB	108.8 (11)
O1—Na3—O7Wⁱⁱ	89.260 (18)	Na2—O5W—Na3	120.57 (2)
O1—Na3—O8Wⁱⁱ	103.275 (18)	Na2—O5W—H5WA	99.2 (8)
O1—Na3—O11W^iv	164.843 (19)	Na2—O5W—H5WB	115.8 (8)
O5W—Na3—O1	98.056 (19)	Na3—O5W—H5WA	104.6 (8)
O5W—Na3—O6W	89.307 (18)	Na3—O5W—H5WB	110.4 (8)
O5W—Na3—O7Wⁱⁱ	171.710 (19)	H5WA—O5W—H5WB	103.3 (11)
O5W—Na3—O8Wⁱⁱ	100.594 (19)	Na3—O6W—H6WA	119.0 (8)
O5W—Na3—O11W^iv	81.906 (18)	Na3—O6W—H6WB	99.5 (8)
O7Wⁱⁱ—Na3—O6W	87.087 (18)	Na4—O6W—Na3	87.121 (18)
O8Wⁱⁱ—Na3—O6W	163.889 (19)	Na4—O6W—H6WA	119.3 (8)
O8Wⁱⁱ—Na3—O7Wⁱⁱ	81.375 (17)	Na4—O6W—H6WB	125.4 (8)
O8Wⁱⁱ—Na3—O11W^iv	91.578 (17)	H6WA—O6W—H6WB	104.4 (11)
O11W^iv—Na3—O6W	77.146 (17)	Na3ⁱⁱ—O7W—Na4	169.88 (2)
O11W^iv—Na3—O7Wⁱⁱ	90.011 (18)	Na3ⁱⁱ—O7W—H7WA	93.0 (7)
O1—Na4—O2W^v	159.988 (18)	Na3ⁱⁱ—O7W—H7WB	94.6 (7)
O1—Na4—O3Wⁱⁱⁱ	111.510 (19)	Na4—O7W—H7WA	80.0 (7)
O1—Na4—O6W	93.473 (19)	Na4—O7W—H7WB	94.1 (8)
O1—Na4—O7W	94.255 (18)	Na5—O7W—Na3ⁱⁱ	93.036 (19)
O3Wⁱⁱⁱ—Na4—O2W^v	78.629 (17)	Na5—O7W—Na4	85.941 (18)
O3Wⁱⁱⁱ—Na4—O7W	147.855 (19)	Na5—O7W—H7WA	129.0 (7)
O6W—Na4—O2W^v	70.391 (18)	Na5—O7W—H7WB	126.4 (7)
O6W—Na4—O3Wⁱⁱⁱ	81.508 (18)	H7WA—O7W—H7WB	103.5 (10)
O6W—Na4—O7W	77.934 (18)	Na1ⁱⁱ—O8W—H8WA	108.7 (8)
O7W—Na4—O2W^v	71.332 (16)	Na1ⁱⁱ—O8W—H8WB	63.4 (8)
O10W—Na4—O1	116.965 (19)	Na3ⁱⁱ—O8W—Na1ⁱⁱ	89.467 (17)
O10W—Na4—O2W^v	75.406 (17)	Na3ⁱⁱ—O8W—H8WA	107.3 (8)
O10W—Na4—O3Wⁱⁱⁱ	102.604 (19)	Na3ⁱⁱ—O8W—H8WB	144.2 (8)
O10W—Na4—O6W	144.02 (2)	Na5—O8W—Na1ⁱⁱ	131.86 (2)
O10W—Na4—O7W	80.946 (18)	Na5—O8W—Na3ⁱⁱ	91.707 (18)
O7W—Na5—O2W^v	83.498 (18)	Na5—O8W—H8WA	116.7 (8)
O7W—Na5—O8W	85.300 (18)	Na5—O8W—H8WB	90.3 (8)
O7W—Na5—O9W	158.71 (2)	H8WA—O8W—H8WB	103.5 (11)
O7W—Na5—O9W^vi	116.928 (19)	Na5—O9W—Na5^vi	95.644 (19)
O7W—Na5—O10W	85.482 (18)	Na5^vi—O9W—H9WA	121.6 (8)
O8W—Na5—O2W^v	113.288 (19)	Na5—O9W—H9WA	108.6 (8)
O8W—Na5—O10W	161.013 (19)	Na5^vi—O9W—H9WB	108.7 (8)
O9W^vi—Na5—O2W^v	153.12 (2)	Na5—O9W—H9WB	118.8 (8)
O9W—Na5—O2W^v	76.393 (18)	H9WA—O9W—H9WB	104.4 (11)
O9W—Na5—O8W	96.191 (19)	Na4—O10W—Na5	91.035 (19)
O9W^vi—Na5—O8W	87.022 (18)	Na4—O10W—Na6	92.274 (18)
O9W—Na5—O9W^vi	84.355 (19)	Na4—O10W—H10A	112.3 (8)
O9W—Na5—O10W	98.413 (19)	Na4—O10W—H10B	133.7 (8)
O9W^vi—Na5—O10W	82.422 (18)	Na5—O10W—Na6	149.66 (2)
O2^vii—Na6—O3^vii	58.627 (15)	Na5—O10W—H10A	108.0 (8)
O2^vii—Na6—O10W	102.222 (17)	Na5—O10W—H10B	100.1 (8)
O3—Na6—O2^vii	121.259 (19)	Na6—O10W—H10A	98.6 (8)
O3—Na6—O3^vii	84.548 (17)	Na6—O10W—H10B	57.3 (7)
O3—Na6—O10W	90.449 (16)	H10A—O10W—H10B	106.6 (11)
O3^vii—Na6—O10W	56.888 (14)	Na3^ix—O11W—H11A	96.8 (7)
O3—Na6—O11W	107.102 (19)	Na3^ix—O11W—H11B	110.2 (7)
O3—Na6—O12W	126.569 (19)	Na6—O11W—Na3^ix	118.18 (2)
O11W—Na6—O2^vii	90.615 (18)	Na6—O11W—H11A	103.7 (7)
O11W—Na6—O3^vii	147.954 (18)	Na6—O11W—H11B	118.6 (8)
O11W—Na6—O10W	148.828 (18)	H11A—O11W—H11B	105.8 (10)
O12W—Na6—O2^vii	111.333 (19)	Na2ⁱⁱⁱ—O12W—H12A	92.3 (8)
O12W—Na6—O3^vii	117.639 (18)	Na2ⁱⁱⁱ—O12W—H12B	112.9 (8)
O12W—Na6—O10W	69.070 (16)	Na6—O12W—Na2ⁱⁱⁱ	118.81 (2)
O12W—Na6—O11W	79.823 (17)	Na6—O12W—H12A	108.2 (8)
P1—O1—Na3	125.14 (3)	Na6—O12W—H12B	114.4 (8)
P1—O1—Na4	113.58 (3)	H12A—O12W—H12B	107.1 (11)
Na4—O1—Na3	91.501 (18)

Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x+1, −y+1, −z+1; (iii) −x+1, −y, −z; (iv) x−1, y, z; (v) x, y+1, z; (vi) −x+2, −y+2, −z+1; (vii) −x+2, −y+1, −z+1; (viii) x, y−1, z; (ix) x+1, y, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1WA···O1	0.85 (1)	1.83 (1)	2.6704 (7)	171 (1)
O1W—H1WB···O5^ix	0.86 (1)	2.09 (1)	2.9417 (6)	172 (1)
O2W—H2WA···O6W^viii	0.82 (1)	2.47 (1)	3.1079 (8)	136 (1)
O2W—H2WB···O5^ix	0.82 (1)	2.03 (1)	2.8343 (7)	167 (1)
O3W—H3WA···O8^x	0.83 (1)	1.84 (1)	2.6651 (6)	175 (1)
O3W—H3WB···O8^ix	0.85 (1)	2.03 (1)	2.8469 (6)	161 (1)
O4W—H4WA···O7	0.82 (1)	2.04 (1)	2.8552 (6)	173 (1)
O4W—H4WB···O8^x	0.81 (1)	2.00 (1)	2.7987 (7)	170 (1)
O5W—H5WA···O6	0.84 (1)	1.80 (1)	2.6359 (7)	172 (1)
O5W—H5WB···O5^xi	0.83 (1)	2.43 (1)	3.2184 (7)	159 (1)
O6W—H6WA···O8^xi	0.84 (1)	1.95 (1)	2.7557 (6)	159 (1)
O6W—H6WB···O2ⁱⁱ	0.84 (1)	1.84 (1)	2.6508 (6)	160 (1)
O7W—H7WA···O2	0.86 (1)	1.77 (1)	2.6209 (6)	172 (1)
O7W—H7WB···O2ⁱⁱ	0.85 (1)	2.12 (1)	2.9658 (6)	174 (1)
O8W—H8WA···O7ⁱⁱ	0.83 (1)	1.95 (1)	2.7783 (7)	172 (1)
O8W—H8WB···O4^v	0.84 (1)	1.81 (1)	2.6220 (6)	164 (1)
O9W—H9WA···O5^xii	0.82 (1)	1.93 (1)	2.7531 (7)	174 (1)
O9W—H9WB···O3^v	0.84 (1)	1.90 (1)	2.7235 (6)	167 (1)
O10W—H10A···O7^xii	0.83 (1)	1.91 (1)	2.7345 (6)	175 (1)
O10W—H10B···O3^vii	0.85 (1)	1.85 (1)	2.6902 (6)	171 (1)
O11W—H11A···O6ⁱⁱⁱ	0.87 (1)	1.90 (1)	2.7666 (6)	173 (1)
O11W—H11B···O5^ix	0.85 (1)	2.00 (1)	2.8460 (7)	176 (1)
O12W—H12A···O6ⁱⁱⁱ	0.86 (1)	1.90 (1)	2.7438 (7)	168 (1)
O12W—H12B···O7^xii	0.85 (1)	1.97 (1)	2.8165 (6)	171 (1)

Symmetry codes: (ii) −x+1, −y+1, −z+1; (iii) −x+1, −y, −z; (v) x, y+1, z; (vii) −x+2, −y+1, −z+1; (viii) x, y−1, z; (ix) x+1, y, z; (x) −x, −y−1, −z; (xi) −x, −y, −z; (xii) x+1, y+1, z.

Trisodium orthophosphate heptahydrate (Na3PO4H2O7) top

Crystal data top

Na₃(PO₄)(H₂O)₇	D_x = 1.891 Mg m⁻³
M_r = 290.05	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pca2₁	Cell parameters from 9336 reflections
a = 12.3169 (7) Å	θ = 3.1–40.1°
b = 6.5324 (3) Å	µ = 0.44 mm⁻¹
c = 12.6602 (7) Å	T = 100 K
V = 1018.63 (9) Å³	Fragment, colourless
Z = 4	0.28 × 0.19 × 0.10 mm
F(000) = 600

Data collection top

Bruker APEXII CCD diffractometer	6108 reflections with I > 2σ(I)
ω– and φ–scans	R_int = 0.032
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 40.5°, θ_min = 3.1°
T_min = 0.695, T_max = 0.748	h = −22→22
44325 measured reflections	k = −11→11
6462 independent reflections	l = −23→23

Refinement top

Refinement on F²	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F² > 2σ(F²)] = 0.020	w = 1/[σ²(F_o²) + (0.0225P)² + 0.0222P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.046	(Δ/σ)_max = 0.002
S = 1.07	Δρ_max = 0.32 e Å⁻³
6462 reflections	Δρ_min = −0.22 e Å⁻³
192 parameters	Absolute structure: Flack x determined using 2767 quotients [(I⁺)-(I^-)]/[(I⁺)+(I^-)] (Parsons et al., 2013).
15 restraints	Absolute structure parameter: 0.00 (3)

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Na1	0.73222 (3)	0.61661 (6)	0.49574 (3)	0.00846 (6)
Na2	0.54849 (3)	0.70865 (6)	0.64923 (3)	0.00916 (6)
Na3	0.43297 (3)	1.27728 (6)	0.62867 (3)	0.00944 (6)
P1	0.75326 (2)	0.24872 (3)	0.32554 (2)	0.00477 (3)
O1	0.72833 (5)	0.47911 (9)	0.32845 (5)	0.00800 (9)
O2	0.66276 (5)	0.13564 (9)	0.38566 (5)	0.00924 (9)
O3	0.75902 (5)	0.16945 (10)	0.21082 (5)	0.00796 (9)
O4	0.86543 (5)	0.20695 (9)	0.37948 (5)	0.00788 (9)
O1W	0.57966 (5)	0.82117 (10)	0.47986 (5)	0.01029 (10)
H1WA	0.5198 (11)	0.815 (3)	0.4480 (14)	0.028 (4)*
H1WB	0.6126 (15)	0.921 (2)	0.4517 (17)	0.041 (6)*
O2W	0.88619 (5)	0.81072 (10)	0.45322 (5)	0.01096 (10)
H2WA	0.922 (2)	0.755 (3)	0.4035 (17)	0.057 (7)*
H2WB	0.8770 (15)	0.928 (2)	0.4281 (15)	0.035 (5)*
O3W	0.74117 (5)	0.75613 (10)	0.67442 (6)	0.00859 (10)
H3WA	0.7496 (13)	0.683 (3)	0.7294 (12)	0.019 (4)*
H3WB	0.7415 (12)	0.8842 (19)	0.6921 (16)	0.018 (4)*
O4W	0.60995 (5)	1.35459 (9)	0.56927 (5)	0.00912 (9)
H4WA	0.6198 (14)	1.287 (2)	0.5141 (11)	0.021 (4)*
H4WB	0.6484 (15)	1.283 (2)	0.6127 (14)	0.027 (5)*
O5W	0.37190 (5)	0.61919 (9)	0.57759 (5)	0.00872 (9)
H5WA	0.3356 (15)	0.691 (3)	0.6207 (13)	0.025 (4)*
H5WB	0.3699 (16)	0.688 (3)	0.5207 (12)	0.033 (5)*
O6W	0.49639 (5)	0.50744 (10)	0.79038 (7)	0.01433 (12)
H6WA	0.4324 (11)	0.504 (3)	0.8144 (15)	0.033 (5)*
H6WB	0.5315 (13)	0.419 (2)	0.8240 (15)	0.030 (5)*
O7W	0.48839 (5)	1.00429 (9)	0.73831 (5)	0.00970 (10)
H7WA	0.5377 (13)	1.056 (3)	0.7769 (14)	0.034 (5)*
H7WB	0.4388 (13)	0.965 (3)	0.7820 (13)	0.027 (4)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Na1	0.00824 (13)	0.00899 (14)	0.00816 (14)	−0.00015 (11)	0.00008 (11)	−0.00087 (12)
Na2	0.00823 (13)	0.01088 (14)	0.00835 (15)	−0.00081 (11)	0.00028 (11)	0.00097 (12)
Na3	0.00783 (13)	0.01056 (14)	0.00992 (15)	−0.00032 (11)	−0.00038 (11)	0.00150 (12)
P1	0.00497 (6)	0.00469 (6)	0.00464 (6)	−0.00022 (5)	0.00001 (6)	0.00026 (6)
O1	0.0102 (2)	0.00554 (19)	0.0083 (2)	0.00096 (15)	0.0004 (2)	0.00007 (19)
O2	0.0082 (2)	0.0103 (2)	0.0092 (2)	−0.00266 (18)	0.00143 (19)	0.0019 (2)
O3	0.0108 (2)	0.0076 (2)	0.0055 (2)	0.00040 (17)	−0.00007 (17)	−0.00092 (18)
O4	0.0058 (2)	0.0095 (2)	0.0083 (2)	0.00073 (17)	−0.00134 (17)	0.00040 (19)
O1W	0.0096 (2)	0.0104 (2)	0.0110 (3)	−0.00099 (18)	−0.0012 (2)	0.0037 (2)
O2W	0.0125 (2)	0.0097 (2)	0.0107 (3)	−0.0005 (2)	0.0010 (2)	0.0026 (2)
O3W	0.0102 (2)	0.0075 (2)	0.0081 (2)	0.00052 (17)	−0.00060 (18)	−0.00046 (18)
O4W	0.0087 (2)	0.0099 (2)	0.0088 (2)	0.00065 (17)	−0.00025 (19)	0.0004 (2)
O5W	0.0086 (2)	0.0095 (2)	0.0080 (2)	0.00113 (17)	0.0008 (2)	0.0004 (2)
O6W	0.0109 (2)	0.0158 (3)	0.0163 (3)	0.0056 (2)	0.0050 (2)	0.0084 (2)
O7W	0.0093 (2)	0.0105 (2)	0.0093 (3)	−0.0020 (2)	0.00029 (19)	0.00024 (18)

Geometric parameters (Å, º) top

Na1—O1	2.3010 (8)	Na2—O4Wⁱ	2.6357 (7)
Na1—O1W	2.3146 (7)	Na3—O4W	2.3605 (7)
Na1—O2W	2.3440 (7)	Na3—O7W	2.3606 (7)
Na1—O3W	2.4413 (8)	Na3—O2Wⁱⁱⁱ	2.3656 (8)
Na1—O4Wⁱ	2.4626 (7)	Na3—O3Wⁱⁱⁱ	2.4421 (8)
Na1—O5Wⁱⁱ	2.5311 (7)	Na3—O5W^iv	2.4439 (7)
Na2—O1W	2.2991 (7)	Na3—O6W^iv	2.6575 (10)
Na2—O6W	2.3093 (8)	P1—O1	1.5365 (6)
Na2—O7W	2.3558 (7)	P1—O2	1.5386 (6)
Na2—O3W	2.4146 (7)	P1—O3	1.5435 (7)
Na2—O5W	2.4279 (7)	P1—O4	1.5652 (6)

O1—Na1—O1W	97.38 (3)	Na2—O1W—H1WA	106.5 (13)
O1—Na1—O2W	90.95 (3)	Na1—O1W—H1WA	136.3 (14)
O1W—Na1—O2W	108.94 (3)	Na2—O1W—H1WB	135.9 (15)
O1—Na1—O3W	178.26 (3)	Na1—O1W—H1WB	95.4 (13)
O1W—Na1—O3W	84.36 (3)	H1WA—O1W—H1WB	104.9 (19)
O2W—Na1—O3W	88.53 (3)	Na1—O2W—Na3^v	81.37 (2)
O1—Na1—O4Wⁱ	93.66 (2)	Na1—O2W—H2WA	110.7 (17)
O1W—Na1—O4Wⁱ	86.42 (2)	Na3^v—O2W—H2WA	117.8 (19)
O2W—Na1—O4Wⁱ	163.26 (3)	Na1—O2W—H2WB	118.3 (13)
O3W—Na1—O4Wⁱ	86.38 (2)	Na3^v—O2W—H2WB	127.7 (14)
O1—Na1—O5Wⁱⁱ	98.83 (2)	H2WA—O2W—H2WB	101 (2)
O1W—Na1—O5Wⁱⁱ	159.85 (3)	Na2—O3W—Na1	77.60 (2)
O2W—Na1—O5Wⁱⁱ	82.72 (2)	Na2—O3W—Na3^v	155.23 (4)
O3W—Na1—O5Wⁱⁱ	79.46 (2)	Na1—O3W—Na3^v	77.91 (2)
O4Wⁱ—Na1—O5Wⁱⁱ	80.67 (2)	Na2—O3W—H3WA	99.0 (11)
O1W—Na2—O6W	161.83 (3)	Na1—O3W—H3WA	123.6 (14)
O1W—Na2—O7W	103.70 (3)	Na3^v—O3W—H3WA	91.4 (11)
O6W—Na2—O7W	90.51 (3)	Na2—O3W—H3WB	99.4 (10)
O1W—Na2—O3W	85.30 (3)	Na1—O3W—H3WB	126.9 (14)
O6W—Na2—O3W	104.12 (3)	Na3^v—O3W—H3WB	98.2 (10)
O7W—Na2—O3W	98.07 (3)	H3WA—O3W—H3WB	109.3 (18)
O1W—Na2—O5W	83.00 (2)	Na3—O4W—Na1^iv	146.50 (3)
O6W—Na2—O5W	84.44 (3)	Na3—O4W—Na2^iv	78.47 (2)
O7W—Na2—O5W	95.43 (2)	Na1^iv—O4W—Na2^iv	73.20 (2)
O3W—Na2—O5W	163.89 (3)	Na3—O4W—H4WA	106.6 (12)
O1W—Na2—O4Wⁱ	82.79 (2)	Na1^iv—O4W—H4WA	88.0 (12)
O6W—Na2—O4Wⁱ	82.97 (3)	Na2^iv—O4W—H4WA	145.9 (13)
O7W—Na2—O4Wⁱ	173.46 (3)	Na3—O4W—H4WB	100.9 (14)
O3W—Na2—O4Wⁱ	83.17 (2)	Na1^iv—O4W—H4WB	106.3 (13)
O5W—Na2—O4Wⁱ	84.41 (2)	Na2^iv—O4W—H4WB	112.7 (13)
O4W—Na3—O7W	94.70 (3)	H4WA—O4W—H4WB	99.5 (17)
O4W—Na3—O2Wⁱⁱⁱ	88.73 (3)	Na2—O5W—Na3ⁱ	81.11 (2)
O7W—Na3—O2Wⁱⁱⁱ	116.04 (3)	Na2—O5W—Na1^vi	155.28 (3)
O4W—Na3—O3Wⁱⁱⁱ	171.10 (3)	Na3ⁱ—O5W—Na1^vi	76.19 (2)
O7W—Na3—O3Wⁱⁱⁱ	94.17 (3)	Na2—O5W—H5WA	95.7 (14)
O2Wⁱⁱⁱ—Na3—O3Wⁱⁱⁱ	88.02 (3)	Na3ⁱ—O5W—H5WA	119.9 (13)
O4W—Na3—O5W^iv	90.25 (2)	Na1^vi—O5W—H5WA	104.0 (14)
O7W—Na3—O5W^iv	159.23 (3)	Na2—O5W—H5WB	102.5 (13)
O2Wⁱⁱⁱ—Na3—O5W^iv	84.18 (3)	Na3ⁱ—O5W—H5WB	135.9 (15)
O3Wⁱⁱⁱ—Na3—O5W^iv	81.18 (2)	Na1^vi—O5W—H5WB	87.4 (14)
O4W—Na3—O6W^iv	81.54 (2)	H5WA—O5W—H5WB	103.7 (18)
O7W—Na3—O6W^iv	83.65 (3)	Na2—O6W—Na3ⁱ	78.90 (3)
O2Wⁱⁱⁱ—Na3—O6W^iv	158.82 (3)	Na2—O6W—H6WA	123.6 (13)
O3Wⁱⁱⁱ—Na3—O6W^iv	98.76 (3)	Na3ⁱ—O6W—H6WA	89.3 (13)
O5W^iv—Na3—O6W^iv	77.13 (2)	Na2—O6W—H6WB	129.9 (13)
O1—P1—O2	108.28 (3)	Na3ⁱ—O6W—H6WB	98.9 (13)
O1—P1—O3	111.12 (4)	H6WA—O6W—H6WB	106.2 (18)
O2—P1—O3	109.74 (4)	Na2—O7W—Na3	115.38 (3)
O1—P1—O4	109.68 (3)	Na2—O7W—H7WA	112.1 (13)
O2—P1—O4	109.87 (4)	Na3—O7W—H7WA	104.2 (14)
O3—P1—O4	108.15 (4)	Na2—O7W—H7WB	106.6 (12)
P1—O1—Na1	113.60 (4)	Na3—O7W—H7WB	113.3 (12)
Na2—O1W—Na1	82.53 (2)	H7WA—O7W—H7WB	105 (2)

Symmetry codes: (i) x, y−1, z; (ii) x+1/2, −y+1, z; (iii) x−1/2, −y+2, z; (iv) x, y+1, z; (v) x+1/2, −y+2, z; (vi) x−1/2, −y+1, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H1WA···O4^vi	0.84 (1)	2.09 (1)	2.9344 (9)	176 (2)
O1W—H1WB···O2^iv	0.85 (1)	1.74 (1)	2.5865 (9)	172 (2)
O2W—H2WA···O6W^vii	0.85 (1)	2.38 (1)	3.2042 (11)	163 (2)
O2W—H2WB···O4^iv	0.84 (1)	1.93 (1)	2.7634 (9)	175 (2)
O3W—H3WA···O1^viii	0.85 (1)	1.85 (1)	2.6867 (9)	168 (2)
O3W—H3WB···O3^ix	0.87 (1)	1.88 (1)	2.7391 (9)	172 (2)
O4W—H4WA···O2^iv	0.84 (1)	1.97 (1)	2.8058 (9)	173 (2)
O4W—H4WB···O3^ix	0.86 (1)	1.84 (1)	2.6978 (9)	171 (2)
O5W—H5WA···O3^x	0.85 (1)	1.87 (1)	2.7114 (9)	173 (2)
O5W—H5WB···O4^vi	0.85 (1)	1.92 (1)	2.7544 (9)	169 (2)
O6W—H6WA···O1^x	0.85 (1)	1.99 (1)	2.8109 (9)	163 (2)
O6W—H6WB···O4^viii	0.84 (1)	2.01 (1)	2.8323 (9)	169 (2)
O7W—H7WA···O4^ix	0.85 (1)	2.02 (1)	2.8616 (9)	170 (2)
O7W—H7WB···O2^x	0.86 (1)	1.93 (1)	2.7894 (9)	175 (2)

Symmetry codes: (iv) x, y+1, z; (vi) x−1/2, −y+1, z; (vii) −x+3/2, y, z−1/2; (viii) −x+3/2, y, z+1/2; (ix) −x+3/2, y+1, z+1/2; (x) −x+1, −y+1, z+1/2.

Coordination environments in Na₃(PO₄)(H₂O)₇ and Na₃(PO₄)(H₂O)₆, and results of BVS calculations (H atoms not taken into account) top

Atom	Number of coordination partners	Polyhedron (idealized point group symmetry; deviation δ from it)	Range of M—O bond lengths (Å)	Average M—O bond length (Å)	Number of water molecules in the first coordination sphere (Na—O < 3.0 Å); number of accepted hydrogen bonds	BVS (v.u.)
Na₃(PO₄)(H₂O)₇
Na1	6	Bailar twist (dynamic) (32; 6.105)	2.3009 (8)–2.5307 (8)	2.399	5	1.19
Na2	6	Bailar twist (dynamic) (32; 7.566)	2.2989 (8)–2.6359 (8)	2.407	6	1.16
Na3	6	Bailar twist (dynamic) (32; 7.357)	2.3604 (8)–2.6575 (10)	2.438	6	1.08
P1	4	tetrahedron (43m; 1.306)	1.5367 (6)–1.5655 (7)	1.546	–	4.93
O1	2				2	1.50
O2	1				3	1.26
O3	1				3	1.25
O4	1				5	1.17
O1W	2				–	0.47
O2W	2				–	0.43
O3W	3				–	0.53
O4W	3				–	0.48
O5W	3				–	0.49
O6W	2				1	0.36
O7W	2				–	0.43

Na₃(PO₄)(H₂O)₆
Na1	5	Ψ-1 octahedron (4mm; 22.301)	2.3505 (6)–2.5944 (5)	2.418	3	0.98
Na2	6	twisted trigonal prism (32; 6.248)	2.3508 (5)–2.5269 (6)	2.428	6	1.08
Na3	6	twisted trigonal prism (32; 7.483)	2.3549 (5)–2.5365 (6)	2.433	5	1.07
Na4	6	trigonal antifrustum (3m; 12.318)	2.3115 (5)–2.9741 (6)	2.485	5	1.08
Na5	6	twisted trigonal prism (32; 6.907)	2.3151 (5)–2.5838 (6)	2.395	6	1.18
Na6	6	isosceles wedge (mm2; 22.202)	2.3321 (5)–2.9641 (5)	2.533	3	0.96
P1	4	tetrahedron (43m; 0.995)	1.5336 (5)–1.5525 (5)	1.544	–	4.92
P2	4	tetrahedron (43m; 0.823)	1.5348 (5)–1.5509 (5)	1.545	–	4.95
O1	3				1	1.69
O2	2				3	1.41
O3	3				2	1.54
O4	3				1	1.70
O5	1				5	1.21
O6	1				3	1.26
O7	1				4	1.22
O8	1				4	1.21
O1W	2				–	0.41
O2W	3				–	0.36
O3W	2				–	0.42
O4W	2				–	0.34
O5W	2				–	0.43
O6W	2				1	0.36
O7W	3				–	0.52
O8W	3				–	0.49
O9W	2				–	0.46
O10W	3				–	0.48
O11W	2				–	0.36
O12W	2				–	0.35

Acknowledgements

Dr Christian Litterscheid (Budenheim KG, Germany) kindly provided samples of Na₃(PO₄)(H₂O)₆. The authors acknowledge TU Wien Bibliothek for financial support through its Open Access Funding Program.

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