Inorganic coordination polymers. XII. Chromium(III) tris(phosphinates)

Cohesive films of a series of chromium(III) tris(phosphinates)[Cr(OPRR′O)(OPR″‐R‴O)(OPR*R**O)]y in which the side groups on the phosphorus are alkyl, phenyl, and/or hydrogen groups have been prepared by reaction casting or by hot pressing. The preparative reaction appears to involve conversion of an aquahydroxo or hydroxo chromium(III) bis(phosphinate) to an intermediate hydroxo bis(phosphinate) containing coordinated phosphinic acid followed by an intrachain reaction leading to the tris(phosphinate). Tensile strengths of the chromium(III) tris(phosphinates) range from 100 to 5600 psi, elongations from less than 1 to 100%. Thermogravimetric data indicate that major decomposition occurs at temperatures from 200 to 435°C in air and from 410 to 510°C in nitrogen. Infrared spectra and physical properties are interpreted to support a structure for the chromium(III) tris(phosphinates) which is based on linear, triple‐bridged chains. The presence of octyl or other long alkyl side groups on the phosphorus improves the physical properties, presumably by internal plasticization, but leads to decreased thermal stability.