The cyclo-tetra­phosphate Cd2P4O12, a member of the isotypic series M2P4O12 (M = Mg, Mn, Fe, Co, Ni, Cu)

Weil, M.

doi:10.1107/S1600536810040195

inorganic compounds

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Volume 66| Part 11| November 2010| Page i75

https://doi.org/10.1107/S1600536810040195

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The cyclo-tetraphosphate Cd₂P₄O₁₂, a member of the isotypic series M₂P₄O₁₂ (M = Mg, Mn, Fe, Co, Ni, Cu)

Matthias Weil ^a ^*

^aInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, Vienna University of Technology, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria
^*Correspondence e-mail: mweil@mail.zserv.tuwien.ac.at

(Received 1 October 2010; accepted 7 October 2010; online 13 October 2010)

The title compound, Cd₂P₄O₁₂, dicadmium cyclo-tetraphosphate, crystallizes isotypically with the members of the series M^II₂P₄O₁₂, where M = Mg, Mn, Fe, Co, Ni or Cu. Two CdO₆ octahedra, one with 2 and one with $[\overline{1}]$ symmetry, share corners with the centrosymmetric P₄O₁₂⁴⁻ ring anion that is built up from four corner-sharing PO₄ tetrahedra. The isolated ring anions are arranged in layers parallel to (10 $[\overline{1}]$ ) with the CdO₆ octahedra situated between these layers. The main difference between the individual M^II₂P₄O₁₂ structures pertains to the different sizes of the MO₆ octahedra whereas the geometric parameters of all cyclo-P₄O₁₂⁴⁻ anions are very similar.

Related literature

For a previous powder X-ray study of Cd₂P₄O₁₂, see: Laügt et al. (1973 ). The structure of the low-temperature α-modification of the catena-polyphosphate Cd(PO₃)₂ was refined by Bagieu-Beucher et al. (1974 ). For isotypic M^II₂P₄O₁₂ structures, see: Nord & Lindberg (1975 ) for M = Mg; Glaum et al. (2002 ) for Mn; Nord et al. (1990 ) and Genkina et al. (1985 ) for Fe; Nord (1982 ) and Olbertz et al. (1998 ) for Co; Nord (1983 ) and Olbertz et al. (1998) for Ni; Laügt et al. (1972 ) for Cu. A review on the crystal chemistry of phosphates was published by Durif (1995 ). Ionic radii were compiled by Shannon (1976 ).

Experimental

Crystal data

Cd₂P₄O₁₂
M_r = 540.68
Monoclinic, C 2/c
a = 12.3342 (2) Å
b = 8.6373 (2) Å
c = 10.4037 (2) Å
β = 119.402 (1)°
V = 965.59 (3) Å³
Z = 4
Mo Kα radiation
μ = 5.13 mm⁻¹
T = 296 K
0.36 × 0.24 × 0.12 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ) T_min = 0.260, T_max = 0.578
11480 measured reflections
3001 independent reflections
2936 reflections with I > 2σ(I)
R_int = 0.036

Refinement

R[F² > 2σ(F²)] = 0.023
wR(F²) = 0.054
S = 1.23
3001 reflections
85 parameters
Δρ_max = 2.08 e Å⁻³
Δρ_min = −1.04 e Å⁻³

Table 1
Selected bond lengths (Å)

Cd1—O1ⁱ	2.1875 (12)
Cd1—O6	2.3034 (10)
Cd1—O2ⁱⁱ	2.3690 (11)
Cd2—O5ⁱⁱⁱ	2.2037 (12)
Cd2—O6	2.2563 (11)
Cd2—O2	2.2809 (11)
P1—O1	1.4624 (12)
P1—O2	1.5052 (11)
P1—O3^iv	1.5840 (12)
P1—O4	1.5983 (11)
P2—O5	1.4604 (12)
P2—O6	1.5011 (11)
P2—O3	1.5848 (12)
P2—O4	1.5918 (12)
Symmetry codes: (i) $[x+{\script{1\over 2}}, y+{\script{1\over 2}}, z]$ ; (ii) $[-x+{\script{1\over 2}}, -y+{\script{1\over 2}}, -z]$ ; (iii) $[-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iv) -x, -y+1, -z.

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS for Windows (Dowty, 2006 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536810040195/mg2104sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810040195/mg2104Isup2.hkl

checkCIF report

Comment top

M^II₂P₄O₁₂ compounds containing the cyclo-tetraphosphate anion P₄O₁₂^4- have been the subject of numerous crystallographic studies. Except for Cd₂P₄O₁₂ (X-ray powder data; Laügt et al., 1973), detailed structure data are available for Mg₂P₄O₁₂ (Nord & Lindberg, 1975), Mn₂P₄O₁₂ (Glaum et al., 2002), Fe₂P₄O₁₂ (Nord et al., 1990; Genkina et al., 1985), Co₂P₄O₁₂ (Nord, 1982; Olbertz et al., 1998), Ni₂P₄O₁₂ (Nord, 1983; Olbertz et al., 1998) and Cu₂P₄O₁₂ (Laügt et al., 1972). During experiments intended for crystal growth of large single crystals of the low-temperature modification of cadmium catena-polyphosphate, α-Cd(PO₃)₂ (Bagieu-Beucher et al., 1974), single crystals of the title compound were obtained instead.

The crystal structures of the isotypic M^II₂P₄O₁₂ family are built up from centrosymmetric P₄O₁₂^4- ring anions. The isolated anions are arranged in layers parallel to (101). Two sets of slightly distorted MO₆ octahedra, one with 1 symmetry and one with 2 symmetry, share edges and are situated in the interlayer space. The three-dimensional framework is accomplished by corner-sharing of the MO₆ units and the P₄O₁₂^4- anions. Figures 1 and 2 show the resulting arrangement for Cd₂P₄O₁₂.

The P₄O₁₂^4- ring anion of Cd₂P₄O₁₂ (Fig. 3) consists of four corner-sharing PO₄ tetrahedra and shows the typical features with respect to bond lengths and angles, i.e. shorter terminal P—O bonds and longer P—O bonds to the bridging O atoms. A review on structures containing the cyclo-tetraphosphate anion has been given by Durif (1995) where characteristic distances and angles are compiled. The individual bond lengths and angles of the P₄O₁₂^4- anions are very similar in all M^II₂P₄O₁₂ structures. The main difference between the structures is related to the varying ionic radii of the M^II cations. Correspondingly, the MO₆ octahedra show (slight) variations in the M—O bond lengths. In the M^II₂P₄O₁₂ family (M = Mg, Mn, Fe, Co, Ni, Cu, and Cd), Cd^II has the largest ionic radius (0.95 Å) for coordination number 6 (Shannon, 1976). This value seems to be the upper limit for the existence of the M^II₂P₄O₁₂ family of structures. For larger M^II cations like Hg^II or Pb^II (ionic radius 1.02 Å and 1.19 Å, respectively) solely long-chain catena-polyphosphate structures M(PO₃)₂ are realised.

In the review on condensed phosphates given by Durif it was stated that cyclo-Cd₂P₄O₁₂ transforms irreversibly into the low-temperature α-modification of the long-chain polyphosphate Cd(PO₃)₂ by prolonged heating at 573 K (Durif, 1995, and references therein), indicating that this transformation process is kinetically controlled. This assumption is confirmed by DSC (differential scanning calorimetry) measurements of the current sample (N₂ atmosphere, heating rate 10 K^.min^-1). Whereas no phase transition has been observed for this compound up to 873 K under these conditions, heating the sample at 873 K in a laboratory furnace under atmospheric conditions for 20 h resulted in a complete transformation into α-Cd(PO₃)₂.

Related literature top

For a previous powder X-ray study of Cd₂P₄O₁₂, see: Laügt et al. (1973). The structure of the low-temperature α-modification of the catena-polyphosphate Cd(PO₃)₂ was refined by Bagieu-Beucher et al. (1974). For isotypic M^II₂P₄O₁₂ structures, see: Nord & Lindberg (1975) for M = Mg; Glaum et al. (2002) for Mn; Nord et al. (1990) and Genkina et al. (1985) for Fe; Nord (1982) and Olbertz et al. (1998) for Co; Nord (1983) and Olbertz et al. (1998) for Ni; Laügt et al. (1972) for Cu. A review on the crystal chemistry of phosphates was published by Durif (1995). Ionic radii were compiled by Shannon (1976).

Experimental top

Single crystals suitable for X-ray structure analysis were grown using the phosphate flux method. CdO (0.7 g) was placed in a glassy carbon crucible and was covered carefully with 70%_wt H₃PO₄ (5.4 g). The crucible was subjected to the following temperature programme: RT → 693 K [3 h] → 693 K [5 h] → 573 K [48 h]. Then the crucible was removed from the furnace. Prismatic colourless crystals with maximum edge lengths of 1.5 mm were obtained by leaching the phosphate flux with warm water.

Structure description top

For a previous powder X-ray study of Cd₂P₄O₁₂, see: Laügt et al. (1973). The structure of the low-temperature α-modification of the catena-polyphosphate Cd(PO₃)₂ was refined by Bagieu-Beucher et al. (1974). For isotypic M^II₂P₄O₁₂ structures, see: Nord & Lindberg (1975) for M = Mg; Glaum et al. (2002) for Mn; Nord et al. (1990) and Genkina et al. (1985) for Fe; Nord (1982) and Olbertz et al. (1998) for Co; Nord (1983) and Olbertz et al. (1998) for Ni; Laügt et al. (1972) for Cu. A review on the crystal chemistry of phosphates was published by Durif (1995). Ionic radii were compiled by Shannon (1976).

Computing details top

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ATOMS for Windows (Dowty, 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

	Fig. 1. The crystal structure of Cd₂P₄O₁₂ in a projection along [001]. PO₄ tetrahedra are red, CdO₆ octahedra are blue and O atoms are displayed as white spheres.
	Fig. 2. The crystal structure of Cd₂P₄O₁₂ in a projection along [010]. Colour code as in Fig. 1.
	Fig. 3. The P₄O₁₂ ring anion with displacement ellipsoids drawn at the 99% level. Non-labelled atoms are generated by inversion symmetry. [Symmetry code: (viii) -x, -y + 1, -z.]

dicadmium cyclo-tetraphosphate top

Crystal data top

Cd₂P₄O12	F(000) = 1008
M_r = 540.68	D_x = 3.719 Mg m⁻³
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 9733 reflections
a = 12.3342 (2) Å	θ = 3.0–40.1°
b = 8.6373 (2) Å	µ = 5.13 mm⁻¹
c = 10.4037 (2) Å	T = 296 K
β = 119.402 (1)°	Fragment, colourless
V = 965.59 (3) Å³	0.36 × 0.24 × 0.12 mm
Z = 4

Data collection top

Bruker APEXII CCD diffractometer	3001 independent reflections
Radiation source: fine-focus sealed tube	2936 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.036
ω and φ scans	θ_max = 40.1°, θ_min = 3.0°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −22→22
T_min = 0.260, T_max = 0.578	k = −13→15
11480 measured reflections	l = −18→18

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.023	w = 1/[σ²(F_o²) + (0.0182P)² + 0.873P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.054	(Δ/σ)_max = 0.001
S = 1.23	Δρ_max = 2.08 e Å⁻³
3001 reflections	Δρ_min = −1.04 e Å⁻³
85 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0306 (6)

Crystal data top

Cd₂P₄O12	V = 965.59 (3) Å³
M_r = 540.68	Z = 4
Monoclinic, C2/c	Mo Kα radiation
a = 12.3342 (2) Å	µ = 5.13 mm⁻¹
b = 8.6373 (2) Å	T = 296 K
c = 10.4037 (2) Å	0.36 × 0.24 × 0.12 mm
β = 119.402 (1)°

Data collection top

Bruker APEXII CCD diffractometer	3001 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2008)	2936 reflections with I > 2σ(I)
T_min = 0.260, T_max = 0.578	R_int = 0.036
11480 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.023	85 parameters
wR(F²) = 0.054	0 restraints
S = 1.23	Δρ_max = 2.08 e Å⁻³
3001 reflections	Δρ_min = −1.04 e Å⁻³

Special details top

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	U_iso*/U_eq
Cd1	0.5000	0.463931 (16)	0.2500	0.01089 (4)
Cd2	0.2500	0.2500	0.0000	0.00995 (4)
P1	−0.01063 (3)	0.27016 (4)	0.02086 (4)	0.00915 (6)
P2	0.18879 (3)	0.50069 (4)	0.19159 (3)	0.00957 (6)
O1	−0.04856 (12)	0.13811 (15)	0.07757 (14)	0.0192 (2)
O2	0.04150 (11)	0.24122 (13)	−0.08092 (13)	0.01274 (17)
O3	0.12504 (11)	0.61475 (16)	0.05498 (13)	0.0208 (2)
O4	0.08602 (11)	0.37174 (16)	0.15789 (13)	0.0188 (2)
O5	0.21814 (13)	0.57449 (17)	0.33127 (13)	0.0203 (2)
O6	0.29305 (9)	0.42682 (14)	0.17838 (12)	0.01323 (16)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cd1	0.01110 (6)	0.00998 (7)	0.01157 (6)	0.000	0.00555 (4)	0.000
Cd2	0.01135 (6)	0.01049 (7)	0.00858 (6)	0.00011 (3)	0.00534 (4)	0.00030 (3)
P1	0.01011 (12)	0.00779 (13)	0.01007 (12)	0.00002 (9)	0.00536 (9)	0.00080 (9)
P2	0.00955 (12)	0.00927 (14)	0.00907 (11)	0.00068 (10)	0.00393 (9)	−0.00214 (9)
O1	0.0242 (5)	0.0138 (5)	0.0198 (4)	−0.0032 (4)	0.0111 (4)	0.0051 (4)
O2	0.0118 (4)	0.0150 (5)	0.0129 (4)	−0.0001 (3)	0.0072 (3)	−0.0029 (3)
O3	0.0209 (5)	0.0247 (6)	0.0205 (5)	0.0139 (4)	0.0132 (4)	0.0109 (4)
O4	0.0198 (4)	0.0225 (5)	0.0176 (4)	−0.0106 (4)	0.0120 (4)	−0.0095 (4)
O5	0.0245 (5)	0.0202 (6)	0.0146 (4)	−0.0011 (4)	0.0084 (4)	−0.0098 (4)
O6	0.0102 (3)	0.0129 (4)	0.0156 (4)	0.0016 (3)	0.0056 (3)	−0.0030 (3)

Geometric parameters (Å, º) top

Cd1—O1ⁱ	2.1875 (12)	Cd2—Cd1^iv	3.4370
Cd1—O1ⁱⁱ	2.1875 (12)	P1—O1	1.4624 (12)
Cd1—O6ⁱⁱⁱ	2.3034 (10)	P1—O2	1.5052 (11)
Cd1—O6	2.3034 (10)	P1—O3^viii	1.5840 (12)
Cd1—O2^iv	2.3690 (11)	P1—O4	1.5983 (11)
Cd1—O2^v	2.3690 (11)	P2—O5	1.4604 (12)
Cd1—Cd2	3.4370	P2—O6	1.5011 (11)
Cd1—Cd2ⁱⁱⁱ	3.4370	P2—O3	1.5848 (12)
Cd2—O5^vi	2.2037 (12)	P2—O4	1.5918 (12)
Cd2—O5^vii	2.2037 (12)	O1—Cd1^ix	2.1875 (12)
Cd2—O6^iv	2.2563 (11)	O2—Cd1^iv	2.3690 (11)
Cd2—O6	2.2563 (11)	O3—P1^viii	1.5840 (12)
Cd2—O2^iv	2.2809 (11)	O5—Cd2ⁱ	2.2037 (12)
Cd2—O2	2.2809 (11)

O1ⁱ—Cd1—O1ⁱⁱ	93.10 (7)	O5^vii—Cd2—O2	90.06 (5)
O1ⁱ—Cd1—O6ⁱⁱⁱ	90.95 (4)	O6^iv—Cd2—O2	84.63 (4)
O1ⁱⁱ—Cd1—O6ⁱⁱⁱ	100.06 (4)	O6—Cd2—O2	95.37 (4)
O1ⁱ—Cd1—O6	100.06 (4)	O2^iv—Cd2—O2	180.00 (6)
O1ⁱⁱ—Cd1—O6	90.95 (4)	O1—P1—O2	119.08 (8)
O6ⁱⁱⁱ—Cd1—O6	164.00 (6)	O1—P1—O3^viii	107.89 (8)
O1ⁱ—Cd1—O2^iv	174.69 (4)	O2—P1—O3^viii	109.73 (6)
O1ⁱⁱ—Cd1—O2^iv	91.90 (5)	O1—P1—O4	108.33 (7)
O6ⁱⁱⁱ—Cd1—O2^iv	86.40 (4)	O2—P1—O4	109.24 (6)
O6—Cd1—O2^iv	81.64 (4)	O3^viii—P1—O4	101.05 (8)
O1ⁱ—Cd1—O2^v	91.90 (5)	O5—P2—O6	118.14 (7)
O1ⁱⁱ—Cd1—O2^v	174.69 (4)	O5—P2—O3	113.12 (8)
O6ⁱⁱⁱ—Cd1—O2^v	81.64 (4)	O6—P2—O3	104.61 (6)
O6—Cd1—O2^v	86.40 (4)	O5—P2—O4	107.83 (7)
O2^iv—Cd1—O2^v	83.17 (6)	O6—P2—O4	107.92 (7)
O5^vi—Cd2—O5^vii	180.0	O3—P2—O4	104.28 (8)
O5^vi—Cd2—O6^iv	93.87 (5)	P1—O1—Cd1^ix	148.67 (8)
O5^vii—Cd2—O6^iv	86.13 (5)	P1—O2—Cd2	121.90 (7)
O5^vi—Cd2—O6	86.13 (5)	P1—O2—Cd1^iv	129.45 (7)
O5^vii—Cd2—O6	93.87 (5)	Cd2—O2—Cd1^iv	95.30 (4)
O6^iv—Cd2—O6	180.00 (5)	P1^viii—O3—P2	139.93 (8)
O5^vi—Cd2—O2^iv	90.06 (5)	P2—O4—P1	138.17 (8)
O5^vii—Cd2—O2^iv	89.94 (5)	P2—O5—Cd2ⁱ	162.37 (10)
O6^iv—Cd2—O2^iv	95.37 (4)	P2—O6—Cd2	119.78 (6)
O6—Cd2—O2^iv	84.63 (4)	P2—O6—Cd1	140.75 (7)
O5^vi—Cd2—O2	89.94 (5)	Cd2—O6—Cd1	97.83 (4)

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

Experimental details

Crystal data
Chemical formula	Cd₂P₄O12
M_r	540.68
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	296
a, b, c (Å)	12.3342 (2), 8.6373 (2), 10.4037 (2)
β (°)	119.402 (1)
V (Å³)	965.59 (3)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	5.13
Crystal size (mm)	0.36 × 0.24 × 0.12

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2008)
T_min, T_max	0.260, 0.578
No. of measured, independent and observed [I > 2σ(I)] reflections	11480, 3001, 2936
R_int	0.036
(sin θ/λ)_max (Å⁻¹)	0.906

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.023, 0.054, 1.23
No. of reflections	3001
No. of parameters	85
Δρ_max, Δρ_min (e Å⁻³)	2.08, −1.04

Computer programs: APEX2 (Bruker, 2008), SAINT (Bruker, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ATOMS for Windows (Dowty, 2006).

Selected bond lengths (Å) top

Cd1—O1ⁱ	2.1875 (12)	P1—O2	1.5052 (11)
Cd1—O6	2.3034 (10)	P1—O3^iv	1.5840 (12)
Cd1—O2ⁱⁱ	2.3690 (11)	P1—O4	1.5983 (11)
Cd2—O5ⁱⁱⁱ	2.2037 (12)	P2—O5	1.4604 (12)
Cd2—O6	2.2563 (11)	P2—O6	1.5011 (11)
Cd2—O2	2.2809 (11)	P2—O3	1.5848 (12)
P1—O1	1.4624 (12)	P2—O4	1.5918 (12)

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

References

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