文摘
Comparison of the X-ray structures of two pairs of dicopper(I) and dicopper(1.5) cryptates provides evidence(over 0.5 Å contraction of the internuclear distance in one pair) for copper-copper bond formation. Althoughresonance Raman spectroscopy fails to identify a pure copper-copper stretching mode, because of extensivemixing of several low-frequency stretching and bending modes, isotopic substitution experiments indicate significantCu-Cu character in a band around 250 cm-1. A normal coordinate analysis broadly supports the spectroscopicfindings. X-ray crystal structures are presented for the dicopper(1.5) complex Cu2imBT(ClO4)3, C18H30Cl3Cu2N8O12,a = 9.140(4) Å, c = 30.35(3) Å, rhombohedral, R32, Z = 3, and the dicopper(I) Cu2imbistrpn(ClO4)2, C24H42Cl2Cu2N8O8, a = 9.279(2) Å, c = 32.846(9) Å, rhombohedral, R32, Z = 3.