Synthesis of a pyridine-containing tetra-aza macrocycle, 7-methyl-3,7,1 1,17-tetra-azabicyclo[11.3.1]heptadeca-1(17),13,15-triene (L1), and characterisation of its nickel(II), copper(II), and zinc(II) complexes. Reduction of the pyridine ring of [Ni(L1)]2+ to give [Ni(L2)]2+(L2= 7-methyl-3,7,11,17-tetra-azabicyclo[11.3.1]heptadecane), and characterisation of [Ni(L2)]2+ by X-ray crystallography

Abstract

The new ligand 7-methyl-3,7,1 1,17-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 = Ni²⁺, Cu²⁺, or Zn²⁺; X^–= ClO₄^– or NO₃^–). The diamagnetic perchlorate salts of Ni²⁺ and Zn²⁺ have been characterised by ¹³C n.m.r. spectroscopy, and found to be single symmetric species in nitromethane solution, whereas the zinc nitrate complex is a mixture of symmetric and asymmetric species. Reaction of [Ni(L¹)][ClO₄]₂ with NCS^–, NO₂^–, or oxalate (ox) ions gives [Ni(L¹)(NCS)₂], [Ni(L¹)(NO₂)(ClO₄)], and [L¹Ni(µ-ox)NiL¹][ClO₄]₂ respectively, of which the thiocyanato- and nitro-complexes are trans-octahedral and in the µ-oxalato-complex the nickel(II) is cis-octahedral. Reduction of the pyridine ring of [Ni(L¹)][ClO₄]₂ with H₂ over Raney nickel gives a symmetric, diamagnetic, square-planar complex, [Ni(L²)][ClO₄]₂, as shown by ¹³C n.m.r., fast atom bombardment mass spectrometry, and the X-ray crystal structure. The crystals are orthorhombic, space group P2₁2₁2₁, with lattice constants a= 12.798(4), b= 9.939(3), c= 16.604(7)Å, and Z= 4; the structure refined to an R value of 0.056 for 1 362 observed reflections. In nitromethane solution, ¹³C n.m.r. spectroscopy shows that this square-planar complex is a mixture of two symmetric isomers.