Notizen: Die Kristallstruktur von Calciumchromat(VI), CaCrO₄ / The Crystal Structure of Calcium Chromate (VI), CaCrO₄

Abstract

The zircon-type structure of calcium chromate( VI), CaCrO4, has been confirmed and refined from single-crystal X-ray data. The compound crystallizes tetragonaly, space group I41/amd, with a = 7.222(2), c = 6.285(1) Å, c/a = 0.8703 and Z = 4. The structure comprises isolated, slightly distorted CrO4 tetrahedra ( C r-O = 1.646(3) Å ) which are connected with CaO8 dodecahedra (<Ca-O> = 2.556 Å) by edge- and corner-sharing. The three-dimensional framework thus created contains rather large holes which are, however, empty in the case of CaCrO4

Surface-Enhanced Raman Spectroscopy (SERS) and Molecular Modeling of the Chromate Interaction with 4-(2-Mercaptoethyl)Pyridinium

“…Using the B3LYP/3-21G* method, the Cr−O bond length was calculated to be 1.646 Å. This value agrees well with the results obtained using other methods, Table S-1, Supporting Information. , It also agrees with the value of 1.647 Å determined crystallographically for CaCrO 4 , in which the chromate ion has tetrahedral site symmetry . Because chromate has tetrahedral symmetry, it should have four vibrational modes all of which are Raman active.…”

“…20,25 It also agrees with the value of 1.647 Å determined crystallographically for CaCrO 4 , in which the chromate ion has tetrahedral site symmetry. 26 Because chromate has tetrahedral symmetry, it should have four vibrational modes all of which are Raman active. The B3LYP/3-21G* method was used to calculate the vibrational modes of chromate.…”

Calcium-43 chemical shift and electric field gradient tensor interplay: a sensitive probe of structure, polymorphism, and hydration

“…This emphasizes that care must be taken when using prior data which correlates calcium d iso with Ca-O bond distances. While we further discuss the topic of the calcium CS tensor of CaCrO 4 in the computational section, we note that GIPAW DFT computations using an accepted crystal structure 61 for CaCrO 4 provide calculated NMR tensor parameters that are in very good agreement with the experimentally observed values.…”

“…Preliminary structural studies of CaCrO 4 using XRD were carried out nearly a century ago by Clouse, 113,114 and relatively recently a slightly modified structure for this material was proposed. 61 The common form of this material belongs to the tetragonal I4 1 /amd space group with the calcium ions at very high symmetry locations (% 4m2, Fig. 1h), which is expected to greatly constrain the resulting EFG and CS tensor parameters for this system.…”

Crystal structural phase transition in CaCrO4under high pressure

“…It is composed of chains of alternating edge-sharing CrO 4 tetrahedra and CaO 8 dodecahedra, as shown in figure 1. The CrO 4 tetrahedra are somewhat elongated because the O-O edges shared with CaO 8 dodecahedra are shorter than the length of the unshared tetrahedral edges [24]. Although the thermodynamic properties of CaCrO 4 have been studied in detail [25][26][27], little is known about its high-pressure structural behaviour.…”