Structural and spectroscopic studies of binuclear Cu2+ and Co2+ complexes with an amide-based naphthalenophane

Binuclear Cu2+ and Co2+ complexes with a chelating naphthalenophane were ch aracterized by single-crystal X- ray analyses, electronic absorption spectr oscopy and luminescence spectroscopy: the naphthalenophane is 2,9,22,29-tet raoxo-4,7,24,27-tetrakis( carboxymethyl)-1,4,7,10,21,24,27,30-octaaza[10.10 ](1.5)naphthalenophane (abbreviated as LH4). The Cu2+ complex crystallized as [Cu2L](0) From acidic solution and [Cu-2(LH-4)](4-) from basic solution: the coordination geometry around each metal ion in [Cu2L](0) is a square p yramid with an amide oxygen atom, two amino nitrogen atoms and two carboxyl ate oxygen atoms; the amide nitrogen atoms in [Cu-2(LH-4)](4-) are deproton ated and construct a square planar coordination geometry together with amin o nitrogen atoms around each metal ion. The formation of the two structures is due to a change in the coordination linkage of the amide groups. [Cu-2( LH (-4))](4-) shows strong metal-ligand charge transfer bands caused by the coordination of the amide nitrogen atoms that are directly bonded to the n aphthyl groups. In the Co2+ complex. [CO2L(H2O)(2)](0), each metal ion has a seven-coordination geometry. the emission and excitation bands in the lum inescence spectra showed a red shift upon metal complexation. In all metal complexes studied. the naphthyl groups are distorted from the planar struct ure. as a result of metal complexation that causes contraction of the macro cyclic rings. (C) 2000 Elsevier Science B.V. All rights reserved.