Inorganic coordination polymers. XI. A new family of chromium(III) bis(phosphinate) polymers, [Cr(OH)(OPRR′O)2]x

Heating hydroxyaquochromium(III) bis(phosphinates) at temperatures up to 200°C under vacuum yields the corresponding anhydrous polymers Cr(OH)(OPRR'O)₂]_x. The infrared and visible spectra and solution properties lead to the following conclusions. When R and R′ are phenyl groups, the hydroxyl groups appear to bridge between adjacent chromium atoms in the chain together with the phosphinate ligands to yield a linear, triple-bridged polymer. When at least one substituent on the phosphorus is an alkyl group, some of the hydroxyl groups crosslink between chains to yield less soluble polymers. Comparison of the properties of these new polymers with the parent polymers suggests that the latter should be formulated Cr(H₂O)_n(OH)(OPRR′O)₂]_x·pH₂O and that they contain more than one kind of monomer unit. The parent polymers can be readily prepared by a new method which involves reaction of a soluble chromium(III) salt with alkali metal phosphinates or of chromium(III) hydroxide with phosphinic acids in a water–tetrahydrofuran mixture.