Radical-ion salts obtained from tetraazaderivatives of nickel and copper and tetracyanoquinodimethane: structural and magnetic characterization

摘要

Several derivatives of formulae [M(N-4)(TCNQ)(2)] and [M(N-4)(TCNQ)(2)](TCNQ) (M = Ni, Cu; N-4 = 1,4,7,10-tetraazacyclododecane ([12] aneN(4)), 1,4,8,11-tetraazacyclotetradecane ([14] aneN(4)), 1,4,8,12-tetraazacyclopentadecane ([15] aneN(4)), 1,4,7,10-tetraazadecane (trien), N,N,N-tris(2-aminoethyl)amine (tren), 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,14-diene (trans-dieneN(4))) have been obtained by metathesis reaction of the corresponding perchlorate or nitrate derivatives and LiTCNQ or (Et3NH)(TCNQ)(2). The compounds [M(aneN(4))(TCNQ)(2)] have a six coordinated metal atom surrounded by the four macrocyclic nitrogens and two nitrogens from sigma coordinated TCNQ(-). The overlap with a neighbouring 7,7,8,8-tetracyanoquinodimethane (TCNQ) forms the diamagnetic dianion [TCNQ](2)(2-), and the whole structure can be seen as chains of metallomacrocyclic cations and TCNQ dianions alternating in the solid. The crystal structure of [Cu([15] aneN(4))(TCNQ)(2)] confirms this fact. With open chain tetraamines the derivatives [Cu(trien)(TCNQ)(2)] and [Cu(tren)(TCNQ)(2)] are proposed to have the copper in a pentacoordinated environment, with only one coordinated TCNQ. In [M(trans-dieneN(4))](TCNQ)(2) both TCNQ(-) are uncoordinated and dimerized, as the crystal structure of the nickel derivative confirms. The derivatives with three TCNQ [M(aneN4)(TCNQ)2](TCNQ) are proposed to have a structure derived from that of the analogous [M(aneN(4))(TCNQ)(2)], based on the metallomacrocycle-[TCNQ](2) chains connected through the extra TCNQ which remains uncoordinated and overlaps with the coordinated anions. This fact lowers the antiferromagnetic coupling inside the dimers and a small contribution for a thermally activated triplet state is observed in the magnetic susceptibility of these compounds. (C) 2003 Elsevier B.V. All rights reserved. [References: 41]