Studies of the pyridine-containing tetra-azamacrocycle 3,7,11-trimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1) and its complexes with Ni2+, Cu2+, and Zn2+. Crystal structures of the unsymmetric isomer of [Ni(L1)][ClO4]2, and the five-co-ordinate complexes [Ni(L1)(dmso)][ClO4]2(dmso = dimethyl sulphoxide) and [Ni(L1)Cl]ClO4

Abstract

The pyridine-containing tetra-azamacrocycle 3,7,11-trimethyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadeca-1 (17),13,15-triene (L¹) has been prepared and isolated, together with its metal complexes of general formula [M(L¹)]X₂(M = Ni, Cu, or Zn; X = ClO₄^– or NO₃^–). Three geometric isomers arise for these complexes due to the possible positions of the three Me–N groups above and below the macrocyclic ligand plane. All three isomers of the diamagnetic four-co-ordinate nickel(II) complex have been characterised by ¹³C n.m.r. spectroscopy, and the structure of the unsymmetric isomer has been established by X-ray crystallography. One of the two symmetric isomers, with Me–N groups at positions 3 and 11 on one side of the macrocyclic plane and with that at position 7 on the opposite side, readily forms five-co-ordinate complexes [Ni(L¹)X][ClO₄]_n[X = Cl^–, NCS^–, or NO₂^–, n= 1; X = co-ordinating solvent, dimethyl sulphoxide (dmso) or H₂O, n= 2]. An analogous zinc(II) complex, [Zn(L¹)(dmso)][ClO₄]₂, has also been isolated. Crystal structures of the nickel(II) complexes, with X = Cl and dmso, show that they are square pyramidal, with the macrocycle folded, with X co-ordinated in the basal plane in a trans position to the pyridine N atom, and with the N⁷ position at the apex. A six-co-ordinate binuclear complex, [(L¹)Ni(µ-ox)Ni(L¹)][ClO₄]₂, containing a bridging oxalate (ox) ion, has also been isolated. Carbon-13 n.m.r. spectra show that the unsolvated complex of L¹ with zinc(II) nitrate is a mixture of symmetric and unsymmetric isomers, whereas the zinc(II) perchlorate complex is a mixture of both symmetric species.