Crystal structures, electron spin resonance, and thermogravimetric analysis of three mixed-valence copper cyanide...

The crystal structures of three mixed-valence copper cyanide alkanolamine polymers are presented, together with thermogravimetric analysis (TGA) and electron spin resonance (ESR) data. In all three structures, a Cu^II moiety on a crystallographic center of symmetry is coordinated by two alkanolamines and links two Cu^ICN chains via cyanide bridging groups to form diperiodic sheets. The sheets are linked together by cuprophilic Cu^I-Cu^I interactions to form a three-dimensional network. In poly[bis(μ-3-aminopropanolato)tetra-μ-cyanido-dicopper(I)dicopper(II)], [Cu₄(CN)₄(C₃H₈NO)₂]_n, 1, propanolamine bases have lost their hydroxyl H atoms and coordinate as chelates to two Cu^II atoms to form a dimeric Cu^II moiety bridged by the O atoms of the bases with Cu^II atoms in square-planar coordination. The ESR spectrum is very broad, indicating exchange between the two Cu^II centers. In poly[bis(2-aminopropanol)tetra-μ-cyanido-dicopper(I)copper(II)], [Cu₃(CN)₄(C₃H₉NO)₂]_n, 2, and poly[bis(2-aminoethanol)tetra-μ-cyanido-dicopper(I)copper(II)], [Cu₃(CN)₄(CH₇NO)₂]_n, 3, a single Cu^II atom links the Cu^ICN chains together via CN bridges. The chelating alkanolamines are not ionized, and the OH groups form rather long bonds in the axial positions of the octahedrally coordinated Cu^II atoms. The coordination geometries of Cu^II in 2 and 3 are almost identical, except that the Cu-O distances are longer in 2 than in 3, which may explain their somewhat different ESR spectra. Thermal decomposition in 2 and 3, but not in 1, begins with the loss of HCN(g), and this can be correlated with the presence of OH protons on the ligands in 2 and 3, which are not present in 1.