RAMAN-SPECTROSCOPY OF 3 AVERAGE-VALENCE DICOPPER CRYPTATES - EVIDENCEFOR COPPER-COPPER BONDING

Comparison of the X-ray structures of two pairs of dicopper(I) and dic opper(l.5) cryptates provides evidence (over 0.5 Angstrom, contraction of the internuclear distance in one pair) for copper-copper bond form ation. Although resonance Raman spectroscopy fails to identify a pure copper-copper stretching mode, because of extensive mixing of several low-frequency stretching and bending modes, isotopic substitution expe riments indicate significant Cu-Cu character in a band around 250 cm(- 1). A normal coordinate analysis broadly supports the spectroscopic fi ndings. X-ray crystal structures are presented for the dicopper(1.5) c omplex Cu(2)imBT(ClO4)(3), C18H30C13Cu2N8O12, a = 9.140(4) Angstrom, c = 30.35(3) Angstrom, rhombohedral, R32, Z = 3, and the dicopper(I) Cu (2)imbistrpn(ClO4)(2), C24H42Cl2Cu2N8O8, a = 9.279(2) Angstrom, c = 32 .846(9) Angstrom, rhombohedral, R32, Z = 3.