The single-crystal electronic properties and stereochemistry of tri-potassium penta(nitro/nitrito)cuprate(II)

Abstract

The polarised single-crystal electronic and 8.s.r. spectra of K3Cu(N02), have been determined and are shown to be consistent with the stereochemistry of the two non-equivalent copper( II) environments present namely, a sevenco-ordinate [CU(NO~)~(ONO),]~-and a cis-distorted six-co-ordinate [Cu(NOz)2(ONO)z(ONO)]3-species. The i.r. spectrum is shown to be compatable with the presence of nitro-and unidentate and bidentate nitritoligands, but cannot distinguish the two types of nitrito-co-ordination. A structural pathway is suggested between the seven-co-ordinate and cis-distorted species.THE complex K3Cu(N0,), (1) has been known for a considerable time l 3 and has aroused much interest 4p5 as a possible five-co-ordinate copper( 11) complex involving five potentially equivalent nitro-ligands. The recent X-ray crystal-structure determination of (1) has established that there are two types of non-equivalent copper(@ ion environments, neither of which is five-coordinate : one involves a seven-co-ordinate pentagonalbipyramidal [CU(NO,),(ONO),]~-anion, and the other a cis-distorted [Cu(NO,),(ONO),(ONO)] 3-anion, Figure l(a) and (b), respectively. The nitrite ligands involve three distinct types of co-ordination,' namely nitro, unidentate nitrito, and bidentate nitrito. As the original e.s.r. spectrum6 of (1) was reported as axial, consistent with an elongated tetragonal-octahedra1 stereochemistry, and as the original electronic spectrum was reported as a single peak at 14 710 cm-l in contrast to the twin peaks predicted for a cis-distorted octahedral structure,8 the electronic properties have been redetermined and are now reported in the light of the known crystal structure of (1).