Crystal chemistry of M[PO{sub 2}(OH){sub 2}]{sub 2}.2H{sub 2}O compounds (M=Mg, Mn, Fe, Co, Ni, Zn, Cd): Structural investigation of the Ni, Zn and Cd salts

Journal Article · Thu Mar 15 00:00:00 EDT 2007 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2006.12.024· OSTI ID:21015734

Koleva, Violeta ^[1]; Effenberger, Herta ^[2]

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1. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl.11, 1113 Sofia (Bulgaria)
2. Institut fuer Mineralogie und Kristallographie, Universitaet Wien, Althanstrasse 14, A-1090 Vienna (Austria)

The compounds M[PO{sub 2}(OH){sub 2}]{sub 2}.2H{sub 2}O (M=Mg, Mn, Fe, Co, Ni, Zn, Cd) were prepared from super-saturated aqueous solutions at room temperature. Single-crystal X-ray structure investigations of members with M=Ni, Zn, Cd were performed at 295 and 120 K. The space-group symmetry is P2{sub 1}/n, Z=2. The unit-cell parameters are at 295/120 K for M=Ni: a=7.240(2)/7.202(2), b=9.794(2)/9.799(2), c=5.313(1)/5.285(1) A, {beta}=94.81(1)/94.38(1){sup o}, V=375.4/371.9 A{sup 3}; M=Zn: a=7.263(2)/7.221(2), b=9.893(2)/9.899(3), c=5.328(1)/5.296(2) A, {beta}=94.79(1)/94.31(2){sup o}, V=381.5/377.5 A{sup 3}; M=Cd: a=7.356(2)/7.319(2), b=10.416(2)/10.423(3), c=5.407(1)/5.371(2) A, {beta}=93.85(1)/93.30(2){sup o}, V=413.4/409.1 A{sup 3}. Layers of corner-shared MO{sub 6} octahedra and phosphate tetrahedra are linked by three of the four crystallographically different hydrogen bonds. The fourth hydrogen bond (located within the layer) is worth mentioning because of the short O{sub h}...O bond distance of 2.57-2.61 A at room temperature (2.56-2.57 A at 120 K); only for M=Mg it is increased to 2.65 A. Any marked temperature-dependent variation of the unit-cell dimension is observed only vertical to the layers. The analysis of the infrared (IR) spectroscopy data evidences that the internal PO{sub 4} vibrations are insensitive to the size and the electronic configuration of the M {sup 2+} ions. The slight strengthening of the intra-molecular P-O bonds in the Mg salt is caused by the more ionic character of the Mg-O bonds. All IR spectra exhibit the characteristic 'ABC trio' for acidic salts: 2900-3180 cm{sup -1} (A band), 2000-2450 cm{sup -1} (B band) and 1550-1750 cm{sup -1} (C band). Both the frequency and the intensity of the A band provide an evidence that the PO{sub 2}(OH){sub 2} groups in M[PO{sub 2}(OH){sub 2}]{sub 2}.2H{sub 2}O compounds form weaker hydrogen bonds as compared with other acidic salts with comparable O...O bond distances of about 2.60 A. The observed shift of the O-H stretching vibrations of the water molecule in the order M=Mg>Mn{approx}Fe{approx}Co>Ni>Zn{approx}Cd has been discussed with respect to the influence of both the character and the strength of M{r_reversible}H{sub 2}O interactions. - Graphical abstract: IR spectroscopy showed the internal PO{sub 4} vibrations to be insensitive to the size and the electronic configuration of the M {sup 2+} ions and reflect the more ionic character of the Mg-O bonds. The observed 'ABC trio' characteristic for acidic salts is discussed. Single-crystal X-ray investigations were performed at 120 and 295 K. One of the four hydrogen bonds is worth mentioning because of the short O{sub h}...O bond distance of 2.57-2.61 A at room temperature (2.56-2.57 A at 120 K)

• OSTI ID: 21015734
• Journal Information: Journal of Solid State Chemistry, Vol. 180, Issue 3; Other Information: DOI: 10.1016/j.jssc.2006.12.024; PII: S0022-4596(07)00003-5; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BOND LENGTHS
CADMIUM COMPOUNDS
COBALT COMPOUNDS
ELECTRONIC STRUCTURE
INFRARED SPECTRA
IONS
IRON COMPOUNDS
LATTICE PARAMETERS
LAYERS
MAGNESIUM COMPOUNDS
MANGANESE COMPOUNDS
MONOCLINIC LATTICES
MONOCRYSTALS
NICKEL COMPOUNDS
PHOSPHATES
SPACE GROUPS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0065-0273 K
TEMPERATURE RANGE 0273-0400 K
ZINC COMPOUNDS