Dicopper complexes derived from 4-amino-2,1,3-benzothiadiazole with versatile co-ordination number and geometry

Abstract

Three dicopper complexes of 4-amino-2,1,3-benzothiadiazole (abt) have been isolated and structurally characterized. The reaction of [Cu(CH₃CN)₄][PF₆] with abt in THF produced [Cu₂(abt)₂(CH₃CN)₄][PF₆]₂·C₆H₁₂ 1·C₆H₁₂, while in acetone, Cu^I template Schiff-base condensation of the amino group of abt with solvent was found to give [Cu₂(ibt)₂(CH₃CN)₄][PF₆]₂ 2 (ibt = 4-isopropylideneamino-2,1,3-benzothiadiazole). In complex 1 there are two crystallographically independent monomeric units in each of which Cu^I is co-ordinated by one N atom on the ring of abt and two acetonitrile molecules; two units are linked to each other by weak binding of the amino group of abt with Cu^I to give a cyclic dinuclear complex. In complex 2 tetrahedral Cu^I centers are bridged by two ibt molecules in a head-to-tail fashion as in 1. Both 1 and 2 have the same metallocyclophane skeletons showing an intramolecular stacking interaction between two parallel aromatic rings and a considerably long Cu· · ·Cu separation [7.220(5) Å for 1, 6.542(4) Å for 2]. Following the same synthetic strategy as used for the synthesis of 2 another dicopper complex [Cu₂(ibt)₂][ClO₄]₂ 3 was obtained, which presents a structural contrast with 2: two Cu^I centers are linearly co-ordinated by two ibt molecules in a head-to-head arrangement which leads to a twisted conformation with a shorter Cu· · ·Cu distance of 2.699(2) Å. In addition, ¹H NMR measurements reveal that 2 can also be formed directly from 1 in acetone solution.