Structure of the β form of calcium pyrophosphate tetrahydrate

Abstract

-Ca 2 P 2 O 7 Á4H 2 O is monoclinic, P2 1 /c, a = 12.287 (6), b = 7.511 (3), c = 10.775 (5) A Ê , and = 112.54 (1) . Five of the terminal O atoms from a pyrophosphate group bind to Ca atoms, together with O atoms from three of the water molecules. The fourth H 2 O forms only hydrogen bonds. Both Ca atoms have coordination number 7 and show characteristics between those of a capped octahedron and a pentagonal bipyramid. The analysis of coordination distortions suggests that regularity and volume ef®ciency of a Ca coordination polyhedron increases with the number of bound water O atoms. The structure is layered after {100}, re¯ected also in the morphology of crystals which are formed as extremely thin plates. The central parts of the layers are formed by chains of Ca coordination polyhedra which run along the b axis and are interconnected by pyrophosphate groups. Water molecules form the surfaces of the layers. A peculiar auto-inhibition of growth from supersaturated solutions is supposed to be caused by a direct attachment of CaP 2 O 7 2À and P 2 O 7 4À to the water molecules on the surfaces of layers. Ca 2 P 2 O 7 Á4H 2 O is known in two polymorphs. The unit-cell volume of the form compared with that of suggests that the former is a low-temperature modi®cation.

Growth and characterization of gel grown calcium pyrophosphate tetrahydrate crystals

“…It is found that the crystal belongs to a monoclinic system with cell parameters as , a =12.287 Å, b= 7.511 Å, c = 10.675 Å and β = 113.57°. The cell parameter data are very closely matching with the values reported by Balić-Žunić et al [15], within the limits of estimated standard deviation. Figure 2 represents the powder XRD pattern with assigned reflections.…”

“…Balić-Žunić et al [15] have determined the crystal structure of CPPT and confirmed that the crystal is having monoclinic system with space group P21/c and the cell parameters were, a= 12.287 Å, b= 7.511 Å and c= 10.677 Å and β = 112.57°. Balić-Žunić et al [15] have carried out the detailed crystal structure study of the β form of CPPT.…”

“…Balić-Žunić et al [15] have carried out the detailed crystal structure study of the β form of CPPT. The main characteristic of the structure parallel to (001) plane is the layers formed by the chains of calcium coordination polyhedra interconnected by phosphate groups.…”

Contribution of calcium-containing crystals to cartilage degradation and synovial inflammation in osteoarthritis

“…CPPD exists in two forms: triclinic and monoclinic, generally abbreviated to t-CPPD and m-CPPD, respectively. A tetrahydrate also exists and is dimorphic, denoted m-CPPTa and m-CPPTb 16 . Characterisation of these forms in the context of their in vivo prevalence has been focussed primarily on microscopy and X-ray powder diffraction (XRPD) studies 17,18 .…”

“…Characterisation of these forms in the context of their in vivo prevalence has been focussed primarily on microscopy and X-ray powder diffraction (XRPD) studies 17,18 . Crystal structures have been determined for t-CPPD 19 , m-CPPTa 20 and m-CPPTb 16 . In addition, the crystal growth and dissolution kinetics of the calcium pyrophosphate hydrate phases have been investigated 21e25 , as has the dehydration 26 .…”