Crystal structure of anhydrous tripotassium citrate from laboratory X-ray powder diffraction data and DFT comparison

Rammohan, A.; Kaduk, J.A.

doi:10.1107/S2056989016011506

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ISSN: 2056-9890

Volume 72| Part 8| August 2016| Pages 1159-1162

https://doi.org/10.1107/S2056989016011506

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Crystal structure of anhydrous tripotassium citrate from laboratory X-ray powder diffraction data and DFT comparison

Alagappa Rammohan ^a and James A. Kaduk ^b ^*

^aAtlantic International University, Honolulu, HI, USA, and ^bIllinois Institute of Technology, Chicago, IL, USA
^*Correspondence e-mail: kaduk@polycrystallography.com

Edited by M. Weil, Vienna University of Technology, Austria (Received 10 June 2016; accepted 14 July 2016; online 19 July 2016)

The crystal structure of anhydrous tripotassium citrate, [K₃(C₆H₅O₇)]_n, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The three unique potassium cations are 6-, 8-, and 6-coordinate (all irregular). The [KO_n] coordination polyhedra share edges and corners to form a three-dimensional framework, with channels running parallel to the c axis. The only hydrogen bond is an intramolecular one involving the hydroxy group and the central carboxylate group, with graph-set motif S(5).

Keywords: crystal structure; powder diffraction; density functional theory; citrate; potassium salt.

CCDC references: 1493594; 1481346; 1493593

1. Chemical context

In the course of a systematic study of the crystal structures of group 1 (alkali metal) citrate salts to understand the anion's conformational flexibility, ionization, coordination tendencies, and hydrogen bonding, we have determined several new crystal structures. Most of the new structures were solved using powder X-ray diffraction data (laboratory and/or synchrotron), but single crystals were used where available. The general trends and conclusions about the 16 new compounds and 12 previously characterized structures are being reported separately (Rammohan & Kaduk, 2016a ). Five of the new structures, viz. NaKHC₆H₅O₇, NaK₂C₆H₅O₇, Na₃C₆H₅O₇, NaH₂C₆H₅O₇, and Na₂HC₆H₅O₇, have been published recently (Rammohan & Kaduk, 2016b ,c ,d ,e ; Rammohan et al., 2016 ), and two additional structures, viz. KH₂C₆H₅O₇ and KH₂C₆H₅O₇(H₂O)₂, have been communicated to the Cambridge Structural Database (Kaduk & Stern, 2016a ,b ).

2. Structural commentary

The asymmetric unit of the title compound is shown in Fig. 1. The r.m.s. deviation of the non-hydrogen atoms between the Rietveld-refined and the DFT-optimized structures is 0.117 Å (Fig. 2). The maximum deviation is 0.260 Å, at O14. The good agreement between the two structures is strong evidence that the experimental structure is correct (van de Streek & Neumann, 2014 ). This discussion uses the DFT-optimized structure. Most of the bond lengths, bond angles, and torsion angles fall within the normal ranges indicated by a Mercury Mogul Geometry Check (Macrae et al., 2008 ). Only the C4—C5 bond length [refined = 1.511 (5), optimized = 1.536, Mogul average = 1.498 (12) Å, Z-score = 3.1], and the C3—C2—C1 [refined = 115 (2), optimized = 115.0, Mogul average = 103 (2)°] and O17—C3—C2 angles [refined = 107 (2), optimized = 109.6, Mogul average = 106 (2)°] are flagged as unusual. The citrate anion occurs in the trans,trans-conformation, which is one of the two low-energy conformations of an isolated citrate. The central carboxylate group and the hydroxy group occur in the normal planar arrangement. Both terminal carboxylate groups O11/O12 and O13/O14 chelate to a single potassium cation (K20 for each). The terminal carboxylate oxygen atom O12 and the hydroxy O17 atom chelate to K21, and the terminal carboxylate oxygen atoms O13 and O17 chelate to K19. The terminal/central pairs O11/O16, O14/O16, O11/O15, and O14/O15 chelate to K21, K19, K19, and K21, respectively. The three potassium cations K19, K20, and K21 are 6-, 8-, and 6-coordinate, respectively (all irregular, using a K—O cut-off distance of 3.24 Å). Their bond-valence sums are 1.12, 1.03, and 1.12 valence units. The metal-oxygen bonding is ionic, based on the cation charges and the Mulliken overlap populations.

Figure 1
The asymmetric unit of the title compound, showing the atom numbering. Atoms are represented by 50% probability spheroids.

Figure 2
Comparison of the refined and optimized structures of anhydrous tripotassium citrate. The refined structure is in red, and the DFT-optimized structure is in blue.

Although the lattice parameters of anhydrous tripotassium citrate are in general similar to those of the monohydrate (Carrell et al., 1987 ; CSD code ZZZHVI01), consistent with the difference in water content, the powder patterns differ considerably. Visual examination of the structures shows that the arrangements of the citrate anions are very different. A mechanism for the transformation of one phase into the other is not obvious.

The Bravais–Friedel–Donnay–Harker (Bravais, 1866 ; Friedel, 1907 ; Donnay & Harker, 1937 ) morphology suggests that we might expect blocky morphology for anhydrous tripotassium citrate, with {011} as the principal faces. A second-order spherical harmonic texture model was included in the refinement. The texture index was only 1.001, indicating that preferred orientation was not significant for this rotated flat plate specimen.

3. Supramolecular features

The [KO_n] coordination polyhedra share edges and corners to form a three-dimensional framework (Fig. 3), with channels running down the c axis. The only hydrogen bond is an intramolecular one (Table 1) involving the hydroxy group and the central carboxylate group, with graph-set motif S(5). The Mulliken overlap population in the hydrogen-acceptor bond is 0.076 e. By the correlation in Rammohan & Kaduk (2016a), this hydrogen bond accounts for 15.1 kcal per mole of crystal energy.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O17—H18⋯O16	0.983	1.814	2.552	129.1

Figure 3
The crystal structure of K₃C₆H₅O₇, viewed down the c axis, with coordination spheres of the potassium cations in polyhedral representation.

4. Database survey

Details of the comprehensive literature search for citrate structures are presented in Rammohan & Kaduk (2016a). A reduced-cell search of the cell of anhydrous tripotassium citrate in the Cambridge Structural Database (Groom et al., 2016 ) (increasing the default tolerance from 1.5 to 2.0%) yielded 208 hits, but limiting the chemistry to C, H, K, and O only resulted in no hits. The powder pattern is now contained in the the Powder Diffraction File (ICDD, 2015 $[ICDD (2015). PDF-4+ 2015 and PDF-4 Organics 2016 (Databases), edited by S. Kabekkodu. International Centre for Diffraction Data, Newtown Square, PA, USA.]$ ) as entry 00-064-1370.

5. Synthesis and crystallization

Potassium citrate monohydrate was synthesized by dissolving 2.0796 g (10.0 mmole) H₃C₆H₅O₇(H₂O) in 20 ml deionized water. 2.0731g K₂CO₃ (15.0 mmole, Sigma-Aldrich) was added to the citric acid solution slowly with stirring. The resulting clear colourless solution was evaporated to dryness in a 333 K oven. The powder pattern matched PDF entry 02-064-1651, confirming the structure as potassium citrate monohydrate (Carrell et al., 1987). The monohydrate was heated at 15 K min⁻¹ to 498 K, and held there for two minutes (the white solid started to discolour). The white solid was removed from the oven, and immediately placed in a sealed glass jar to cool.

6. Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 2. The white solid was ground and blended with NIST SRM 640b Si internal standard in a mortar and pestle. The specimen was protected from the atmosphere by an 8 micron Kapton film attached to the sample holder with petroleum jelly. (The sample hydrates slowly on contact with ambient atmosphere.)

Table 2
Experimental details

	Phase 1	Phase 2
Crystal data
Chemical formula	[K₃(C₆H₅O₇)]	Si
M_r	306.39	28.09
Crystal system, space group	Orthorhombic, Pna2₁	Cubic, Fd $[\overline{3}]$ m
Temperature (K)	300	300
a, b, c (Å)	7.7062 (2), 12.4693 (3), 10.4241 (2)	5.43105, 5.43105, 5.43105
α, β, γ (°)	90, 90, 90	90, 90, 90
V (Å³)	1001.66 (3)	160.20
Z	4	8
Radiation type	Kα₁, Kα₂, λ = 1.540629, 1.544451 Å	Kα₁, Kα₂, λ = 1.540629, 1.544451 Å
Specimen shape, size (mm)	Flat sheet, 24 × 24	Flat sheet, 24 × 24

Data collection
Diffractometer	Bruker D2 Phaser	Bruker D2 Phaser
Specimen mounting	Normal sample holder with Kapton film	Normal sample holder with Kapton film
Data collection mode	Reflection	Reflection
Scan method	Step	Step
2θ values (°)	2θ_min = 4.908, 2θ_max = 69.916, 2θ_step = 0.020	2θ_min = 4.908, 2θ_max = 69.916, 2θ_step = 0.020

Refinement
R factors and goodness of fit	R_p = 0.038, R_wp = 0.049, R_exp = 0.034, R(F²) = 0.059, χ² = 2.103	R_p = 0.038, R_wp = 0.049, R_exp = 0.034, R(F²) = 0.059, χ² = 2.103
No. of parameters	73	73
No. of restraints	29	29
The same symmetry and lattice parameters were used for the DFT calculation. Computer programs: DIFFRAC.Measurement (Bruker, 2009 ), FOX (Favre-Nicolin & Černý, 2002), GSAS (Larson & Von Dreele, 2004), EXPGUI (Toby, 2001), DIAMOND (Crystal Impact, 2015 ) and publCIF (Westrip, 2010 ).

The pattern (Fig. 4) was indexed on a primitive orthorhombic unit cell using ITO (Visser, 1969 ). Manual examination of the systematic absences suggested space group Pna2₁. Pseudo-Voigt profile coefficients were as parameterized in Thompson et al. (1987 ) with profile coefficients for Simpson's rule integration of the Pseudo-Voigt function according to Howard (1982 ). The asymmetry correction of Finger et al. (1994 ) was applied and microstrain broadening by Stephens (1999 ). The structure was solved with FOX (Favre-Nicolin & Černý, 2002 ) using a citrate moiety and three potassium atoms as fragments. The structure was refined by the Rietveld method using GSAS/EXPGUI (Larson & Von Dreele, 2004 ; Toby, 2001 ). All C—C and C—O bond lengths were restrained, as were all bond angles. The hydrogen atoms were included at fixed positions, which were recalculated during the course of the refinement using Materials Studio (Dassault Systemes, 2014 ). The U_iso values of the atoms in the central and outer portions of the citrate anion were constrained to be equal, and the U_iso values of the hydrogen atoms were constrained to be 1.3× those of the atoms to which they are attached.

Figure 4
Rietveld plot for the refinement of K₃C₆H₅O₇. The red crosses represent the observed data points, and the green line is the calculated pattern. The magenta curve is the difference pattern, plotted at the same scale as the other patterns. The vertical scale for angles > 44.0° has been multiplied by a factor of 5. The lower row of black tick marks indicates the reflection positions for the major phase and the upper row of red tick marks is for the silicon internal standard.

The ADDSYM module of PLATON (Spek, 2009 ) suggested the presence of an additional centre of symmetry, and that the space group was Pnam. Refinement in this space group yielded poorer residuals, so we believe that Pna2₁ is the correct space group.

7. DFT calculations

After the Rietveld refinement, a density functional geometry optimization (fixed experimental unit cell) was carried out using CRYSTAL09 (Dovesi et al., 2005 ). The basis sets for the C, H, and O atoms were those of Gatti et al. (1994 ), and the basis set for K was that of Dovesi et al. (1991 ). The calculation used 8 k-points and the B3LYP functional, and took about 66 h on a 2.4 GHz PC. The U_iso values from the Rietveld refinement were assigned to the optimized fractional coordinates.

Supporting information

CCDC references: 1493594; 1481346; 1493593

Crystal structure: contains datablocks KADU1578_publ, kadu1578_DFT, KADU1578_overall, KADU1578_phase_1, KADU1578_phase_2, KADU1578_p_01. DOI: https://doi.org/10.1107/S2056989016011506/wm5301sup1.cif

checkCIF report

Computing details top

Data collection: DIFFRAC.Measurement (Bruker, 2009) for KADU1578_phase_1. Program(s) used to solve structure: FOX (Favre-Nicolin & Černý, 2002) for KADU1578_phase_1. Program(s) used to refine structure: GSAS (Larson & Von Dreele, 2004) and EXPGUI (Toby, 2001) for KADU1578_phase_1. Molecular graphics: DIAMOND (Crystal Impact, 2015) for KADU1578_phase_1. Software used to prepare material for publication: publCIF (Westrip, 2010) for KADU1578_phase_1.

(KADU1578_phase_1) Poly[(µ-2-hydroxypropane-1,2,3-tricarboxylato0tripotassium] top

Crystal data top

[K₃(C₆H₅O₇)]	c = 10.4241 (2) Å
M_r = 306.39	V = 1001.66 (3) Å³
Orthorhombic, Pna2₁	Z = 4
a = 7.7062 (2) Å	T = 300 K
b = 12.4693 (3) Å

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

	x	y	z	U_iso*/U_eq
C1	0.841 (4)	0.883 (3)	0.28611	0.023 (3)*
C2	0.926 (4)	0.915 (3)	0.411 (2)	0.021 (5)*
C3	0.814 (2)	0.8966 (12)	0.532 (3)	0.021 (5)*
C4	0.937 (4)	0.910 (4)	0.647 (3)	0.021 (5)*
C5	0.857 (4)	0.872 (3)	0.771 (3)	0.023 (3)*
C6	0.6539 (18)	0.9724 (11)	0.541 (5)	0.023 (3)*
H7	1.04032	0.90124	0.41652	0.027 (7)*
H8	0.9082	0.99396	0.3928	0.027 (7)*
H9	0.97168	0.98330	0.645913	0.027 (7)*
H10	1.01382	0.84403	0.63413	0.027 (7)*
O11	0.695 (4)	0.9217 (19)	0.252 (4)	0.023 (3)*
O12	0.936 (4)	0.816 (2)	0.226 (4)	0.023 (3)*
O13	0.935 (4)	0.821 (2)	0.859 (4)	0.023 (3)*
O14	0.697 (4)	0.894 (2)	0.787 (4)	0.023 (3)*
O15	0.6828 (17)	1.0726 (11)	0.529 (6)	0.023 (3)*
O16	0.5076 (16)	0.9267 (10)	0.533 (5)	0.023 (3)*
O17	0.7473 (14)	0.7877 (11)	0.525 (5)	0.023 (3)*
H18	0.6543	0.8072	0.525	0.030 (4)*
K19	0.355 (3)	0.8827 (13)	0.743 (3)	0.0442 (17)*
K20	0.1336 (10)	0.7108 (4)	0.021 (3)	0.0442 (17)*
K21	0.148 (3)	0.3753 (14)	0.797 (3)	0.0442 (17)*

Geometric parameters (Å, º) top

C1—C2	1.510 (5)	O13—K20^viii	2.90 (3)
C1—O11	1.278 (9)	O14—C5	1.270 (9)
C1—O12	1.271 (9)	O14—O13	2.18 (3)
C2—C1	1.510 (5)	O14—K19	2.68 (4)
C2—C3	1.544 (4)	O14—K20^viii	2.81 (3)
C2—H7	0.90 (3)	O14—K21ⁱⁱ	2.90 (3)
C2—H8	1.01 (4)	O15—C6	1.275 (8)
C3—C2	1.544 (4)	O15—K19ⁱ	3.05 (6)
C3—C4	1.544 (5)	O15—K20^ix	2.987 (15)
C3—C6	1.553 (4)	O15—K20^x	3.051 (15)
C3—O17	1.452 (8)	O15—K21ⁱⁱ	2.88 (5)
C4—C3	1.544 (5)	O16—C6	1.266 (8)
C4—C5	1.511 (5)	O16—K19	2.55 (4)
C4—H9	0.95 (4)	O16—K21ⁱⁱⁱ	2.81 (4)
C4—H10	1.03 (5)	O17—C3	1.452 (8)
C5—C4	1.511 (5)	O17—H18	0.757 (11)
C5—O13	1.268 (9)	O17—K19ⁱⁱ	3.22 (4)
C5—O14	1.270 (9)	O17—K21^vi	3.23 (4)
C6—C3	1.553 (4)	H18—O17	0.757 (11)
C6—O15	1.275 (8)	K19—O11^x	2.47 (2)
C6—O16	1.266 (8)	K19—O13^xi	2.88 (3)
H7—C2	0.90 (3)	K19—O14	2.68 (4)
H8—C2	1.01 (4)	K19—O15^x	3.05 (6)
H9—C4	0.82 (4)	K19—O16	2.55 (4)
H10—C4	1.03 (5)	K19—O17^xi	3.22 (4)
O11—C1	1.278 (9)	K20—O11^xi	2.96 (3)
O11—K19ⁱ	2.47 (2)	K20—O12^xii	2.93 (3)
O11—K20ⁱⁱ	2.96 (3)	K20—O12^xi	3.18 (3)
O11—K21ⁱⁱⁱ	2.75 (4)	K20—O13^xiii	2.66 (3)
O12—C1	1.271 (9)	K20—O13^xiv	2.90 (3)
O12—K20^iv	2.93 (3)	K20—O14^xiv	2.81 (3)
O12—K20ⁱⁱ	3.18 (3)	K20—O15^xv	2.987 (15)
O12—K21^v	3.37 (4)	K20—O15ⁱ	3.051 (15)
O12—K21^vi	2.58 (3)	K21—O11^xvi	2.75 (4)
O13—C5	1.268 (9)	K21—O12^xvii	2.58 (3)
O13—O14	2.18 (3)	K21—O14^xi	2.90 (3)
O13—K19^iv	3.54 (4)	K21—O15^xi	2.88 (5)
O13—K19ⁱⁱ	2.88 (3)	K21—O16^xvi	2.81 (4)
O13—K20^vii	2.66 (3)	K21—O17^xvii	3.23 (4)

C2—C1—O11	121 (2)	O11^x—K19—O13^xi	152.6 (13)
C2—C1—O12	111 (2)	O11^x—K19—O14	95.5 (9)
O11—C1—O12	128 (2)	O11^x—K19—O15^x	76.6 (11)
C1—C2—C3	115 (2)	O11^x—K19—O16	83.8 (8)
C2—C3—C4	106.0 (13)	O11^x—K19—O17^xi	129.6 (11)
C2—C3—C6	114 (3)	O13^xi—K19—O14	76.3 (11)
C2—C3—O17	107 (2)	O13^xi—K19—O15^x	76.7 (7)
C4—C3—C6	112 (2)	O13^xi—K19—O16	117.0 (10)
C4—C3—O17	111 (2)	O13^xi—K19—O17^xi	76.7 (9)
C6—C3—O17	107.1 (12)	O14—K19—O15^x	85.2 (9)
C3—C4—C5	112 (2)	O14—K19—O16	71.5 (11)
C4—C5—O13	126 (2)	O14—K19—O17^xi	114.2 (10)
C4—C5—O14	116 (2)	O15^x—K19—O16	147.9 (10)
O13—C5—O14	118 (2)	O15^x—K19—O17^xi	141.9 (9)
C3—C6—O15	116.9 (13)	O16—K19—O17^xi	69.7 (7)
C3—C6—O16	115.3 (13)	O11^xi—K20—O12^xii	74.9 (9)
O15—C6—O16	126.2 (16)	O11^xi—K20—O12^xi	43.7 (5)
C1—O11—K19ⁱ	122 (3)	O11^xi—K20—O13^xiii	153.7 (8)
C1—O11—K20ⁱⁱ	98.9 (17)	O11^xi—K20—O13^xiv	105.6 (8)
C1—O11—K21ⁱⁱⁱ	136 (3)	O11^xi—K20—O14^xiv	114.7 (5)
K19ⁱ—O11—K20ⁱⁱ	119.7 (12)	O11^xi—K20—O15^xv	77.6 (12)
K19ⁱ—O11—K21ⁱⁱⁱ	93.6 (11)	O11^xi—K20—O15ⁱ	113.4 (13)
K20ⁱⁱ—O11—K21ⁱⁱⁱ	82.3 (8)	O12^xii—K20—O12^xi	86.3 (8)
C1—O12—K20^iv	162 (3)	O12^xii—K20—O13^xiii	86.2 (5)
C1—O12—K20ⁱⁱ	88.7 (17)	O12^xii—K20—O13^xiv	154.3 (8)
C1—O12—K21^vi	109 (3)	O12^xii—K20—O14^xiv	158.6 (7)
K20^iv—O12—K20ⁱⁱ	81.0 (7)	O12^xii—K20—O15^xv	79.2 (12)
K20^iv—O12—K21^vi	85.8 (9)	O12^xii—K20—O15ⁱ	80.0 (10)
K20ⁱⁱ—O12—K21^vi	84.9 (10)	O12^xi—K20—O13^xiii	154.4 (9)
C5—O13—K19ⁱⁱ	92 (2)	O12^xi—K20—O13^xiv	77.9 (4)
C5—O13—K20^vii	172.2 (18)	O12^xi—K20—O14^xiv	114.1 (8)
C5—O13—K20^viii	96.3 (17)	O12^xi—K20—O15^xv	121.3 (12)
K19ⁱⁱ—O13—K20^vii	86.2 (9)	O12^xi—K20—O15ⁱ	74.6 (10)
K19ⁱⁱ—O13—K20^viii	87.4 (10)	O13^xiii—K20—O13^xiv	99.4 (7)
K20^vii—O13—K20^viii	91.3 (7)	O13^xiii—K20—O14^xiv	77.9 (8)
C5—O14—K19	157 (3)	O13^xiii—K20—O15^xv	81.1 (10)
C5—O14—K20^viii	100.5 (18)	O13^xiii—K20—O15ⁱ	80.1 (10)
C5—O14—K21ⁱⁱ	110 (3)	O13^xiv—K20—O14^xiv	44.9 (6)
K19—O14—K20^viii	87.4 (8)	O13^xiv—K20—O15^xv	126.3 (12)
K19—O14—K21ⁱⁱ	86.0 (11)	O13^xiv—K20—O15ⁱ	76.4 (9)
K20^viii—O14—K21ⁱⁱ	114.1 (12)	O14^xiv—K20—O15^xv	84.2 (14)
C6—O15—K19ⁱ	105 (4)	O14^xiv—K20—O15ⁱ	110.8 (11)
C6—O15—K20^ix	115.2 (11)	O15^xv—K20—O15ⁱ	152.7 (6)
C6—O15—K20^x	162.1 (14)	O11^xvi—K21—O12^xvii	84.5 (12)
C6—O15—K21ⁱⁱ	96 (4)	O11^xvi—K21—O14^xi	84.9 (8)
K19ⁱ—O15—K20^ix	77.8 (11)	O11^xvi—K21—O15^xi	82.9 (9)
K19ⁱ—O15—K20^x	81.7 (12)	O11^xvi—K21—O16^xvi	71.9 (10)
K19ⁱ—O15—K21ⁱⁱ	154.0 (5)	O11^xvi—K21—O17^xvii	119.9 (10)
K20^ix—O15—K20^x	82.4 (3)	O12^xvii—K21—O14^xi	160.0 (12)
K20^ix—O15—K21ⁱⁱ	79.7 (11)	O12^xvii—K21—O15^xi	87.5 (7)
K20^x—O15—K21ⁱⁱ	82.5 (12)	O12^xvii—K21—O16^xvi	110.7 (10)
C6—O16—K19	117 (3)	O12^xvii—K21—O17^xvii	72.0 (9)
C6—O16—K21ⁱⁱⁱ	123 (3)	O14^xi—K21—O15^xi	74.4 (10)
K19—O16—K21ⁱⁱⁱ	120.5 (5)	O14^xi—K21—O16^xvi	81.9 (8)
C3—O17—H18	91.9 (14)	O14^xi—K21—O17^xvii	128.0 (11)
C3—O17—K19ⁱⁱ	119 (2)	O15^xi—K21—O16^xvi	146.8 (10)
C3—O17—K21^vi	123 (2)	O15^xi—K21—O17^xvii	146.4 (9)
K19ⁱⁱ—O17—K21^vi	92.3 (3)	O16^xvi—K21—O17^xvii	66.8 (7)

Symmetry codes: (i) −x+1, −y+2, z−1/2; (ii) x+1/2, −y+3/2, z; (iii) −x+1/2, y+1/2, z−1/2; (iv) x+1, y, z; (v) −x+3/2, y+1/2, z−1/2; (vi) −x+1, −y+1, z−1/2; (vii) x+1, y, z+1; (viii) x+1/2, −y+3/2, z+1; (ix) −x+1/2, y+1/2, z+1/2; (x) −x+1, −y+2, z+1/2; (xi) x−1/2, −y+3/2, z; (xii) x−1, y, z; (xiii) x−1, y, z−1; (xiv) x−1/2, −y+3/2, z−1; (xv) −x+1/2, y−1/2, z−1/2; (xvi) −x+1/2, y−1/2, z+1/2; (xvii) −x+1, −y+1, z+1/2.

(KADU1578_phase_2) Poly[(µ₁₄-2-hydroxypropane-1,2,3-tricarboxylato0tripotassium] top

Crystal data top

Si	V = 160.20 Å³
M_r = 28.09	Z = 8
Cubic, Fd3m	T = 300 K
a = 5.43105 Å

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

	x	y	z	U_iso*/U_eq
Si1	0.125	0.125	0.125	0.01*

Geometric parameters (Å, º) top

Si1—Si1ⁱ	2.3517	Si1—Si1ⁱⁱⁱ	2.3517
Si1—Si1ⁱⁱ	2.3517	Si1—Si1^iv	2.3517

Si1ⁱ—Si1—Si1ⁱⁱ	109.4712	Si1ⁱⁱ—Si1—Si1ⁱⁱⁱ	109.4712
Si1ⁱ—Si1—Si1ⁱⁱⁱ	109.4712	Si1ⁱⁱ—Si1—Si1^iv	109.4712
Si1ⁱ—Si1—Si1^iv	109.4712	Si1ⁱⁱⁱ—Si1—Si1^iv	109.4712

Symmetry codes: (i) x+1/4, y+1/4, −z; (ii) −z, x+1/4, y+1/4; (iii) y+1/4, −z, x+1/4; (iv) −x, −y, −z.

(kadu1578_DFT) top

Crystal data top

[K₃(C₆H₅O₇)]	c = 10.4222 (3) Å
M_r = 306.37	V = 1001.66 Å³
Orthorhombic, PNA2₁	Z = 4
a = 7.7074 (2) Å	Cu Kα radiation, λ = 1.5418 Å
b = 12.4676 (3) Å	T = 300 K

Data collection top

Density functional calculation	k = →
h = →	l = →

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

	x	y	z	U_iso*/U_eq
C1	0.83999	0.87608	0.28090	0.03110*
C2	0.91941	0.91369	0.40840	0.04090*
C3	0.80507	0.89495	0.52759	0.04090*
C4	0.91865	0.91285	0.64734	0.04090*
C5	0.83786	0.87569	0.77456	0.03110*
C6	0.64533	0.97237	0.52736	0.03110*
H7	1.04170	0.87092	0.42230	0.05310*
H8	0.94795	0.99967	0.40314	0.05310*
H9	0.94862	0.99862	0.65281	0.05310*
H10	1.04015	0.86912	0.63386	0.05310*
O11	0.69006	0.90966	0.25219	0.03110*
O12	0.93097	0.81435	0.21142	0.03110*
O13	0.92734	0.81335	0.84433	0.03110*
O14	0.68837	0.91019	0.80291	0.03110*
O15	0.67248	1.07226	0.52772	0.03110*
O16	0.49925	0.92599	0.52665	0.03110*
O17	0.74146	0.78645	0.52713	0.03110*
H18	0.61565	0.79949	0.52593	0.04040*
K19	0.35417	0.87929	0.75053	0.04550*
K20	0.13670	0.70910	0.02740	0.04550*
K21	0.14595	0.37878	0.80253	0.04550*

Bond lengths (Å) top

C1—C2	1.536	C4—C5	1.536
C1—O11	1.265	C4—H9	1.096
C1—O12	1.268	C4—H10	1.093
C2—C3	1.541	C5—O13	1.268
C2—H7	1.093	C5—O14	1.265
C2—H8	1.096	C6—O15	1.263
C3—C4	1.541	C6—O16	1.266
C3—C6	1.564	O17—H18	0.983
C3—O17	1.439

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O17—H18···O16	0.983	1.814	2.552	129.1

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Volume 72| Part 8| August 2016| Pages 1159-1162

https://doi.org/10.1107/S2056989016011506

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research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Crystal structure of anhydrous tripotassium citrate from laboratory X-ray powder diffraction data and DFT comparison

1. Chemical context

2. Structural commentary

3. Supra­molecular features

4. Database survey

5. Synthesis and crystallization

6. Refinement details

7. DFT calculations

Supporting information

References

research communications

3. Supramolecular features