Low-temperature neutron diffraction study of [ReH5(PPh i Pr2)2(SiHPh2)2] and low-temperature X-ray diffraction study of [ReH5(PCyp3)2(SiH2Ph)2]

Inorganic structures in space group P3m1; coordinate analysis and systematic prediction of new ferroelectrics

ICSD Release 2007/1 contains 47 families of inorganic crystal structures, some single-member only, within the 311 entries listed under the polar space group P3m1. Coordinate analysis reveals 12 such families to be candidate ferroelectrics, over a range of confidence levels. Selection is based on the detection of an approach to nonpolar supergroup symmetry, within specified limits, by the atomic arrangement as reported in a confirmed polar space group. The primary source of uncertainty in such predictions is the reliability of the underlying structural determination. The candidates include In2ZnS4, TlSn2F5, Cu7Te4, NaMnSe2, Na2In2(Mo3O8)(MoO4)2, Nb3Br7S, Nb3TeI7, fencooperite, Bi(HCOO)3, Li(NpO2)(CO3)(H2O)2, LiPtD0.66 and Ag3(MoO3F3)(Ag3(MoO4)Cl). A total of 20 structures examined are likely to be nonpolar, a further 20 have reduced predictive properties and three others are more likely to retain P3m1 symmetry over a wide thermal range. Substantial uncertainties associated with many of the listed 163 CdI2, 69 ZnS and 10 SiC polytype structures, together with their low potential for use as possible ferroelectrics, led to their exclusion from fuller analysis.

Theoretical Evaluation of Steric Effects in [ReH(5)(PR(3))(2)(SiR(3))(2)] Complexes with the IMOMM Method

A theoretical study including full geometry optimizations is carried out at the IMOMM(MP2:MM3) (IMOMM = integrated molecular orbital molecular mechanics) computational level on the [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] systems, the results being compared with available experimental diffraction data, as well as with MP2 results on the model system [ReH(5)(PH(3))(2)(SiH(3))(2)]. A simple scheme for the analysis of the relative weight of different contributions to the "steric" distortion is also proposed and applied to the same [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] species.