Axial bonds in copper(II) compounds

Structures and spectroscopic properties of copper(II) compounds of the two cyclam derivatives L-1 and L-2 are reported. L-1 has four 4-cyanobenzyl N-s ubstituents and L-2 has a fused barbiturate ring at one of the two propylen e bridges. The copper(II) complexes of L-1 ([Cu(L-1)(NCCH3)](2+) and [(Cu(L -1)(OH2)](2+)) have trans-I configuration and are five-coordinate with extr emely short axial bonds. The reaction of [(Cu(L-2)(OH)(2)](2+) (purple, six -coordinate, trans-III configuration) with urea and NCS- leads to a blue fi ve-coordinate, and with urea alone to a red four-coordinate species. The Cu N4 chromophores of the three copper(II) compounds of L-2 are close to ident ical, and the color changes are analyzed to be due to the differences in ax ial interactions. (C) 2001 Elsevier Science B.V. All rights reserved.