Pentagonal-pyramidal cadmium(II) and mercury(II) complexes of the quinquedentate macrocyclic ligand 2,15-dimethyl-3,7,10,14,20-penta-azabicyclo[14.3.1]eicosa-1(20),2,14,16,18-pentaene

Abstract

Reaction of 2,6-diacetylpyridine and 4,7-diazadecane-1,10-diamine in methanol in the presence of a stoicheiometric amount of cadmium(II) or mercury(II) halide gives metal complexes of the 17-membered title ligand (L³) in good yield. Derivatives containing [NCS]^– and/or [ClO₄]^– anions have been prepared by metathetical reactions. The crystal and molecular structures of two of the complexes have been determined: [CdL³(Br)]Br·0.5H₂O is orthorhombic, space group Pccn, with a= 11.059(5), b= 12.479(6), c= 31.114(15)Å, and Z= 8; [HgL³(Br)]₂[Hg₂Br₆] is triclinic, space group P with a= 12.577(10), b= 10.485(9), c= 10.098(12)Å, α= 89.49(12), β= 100.98(12), γ= 106.15(14)°, and Z= 1. Diffractometer data for both crystals have been refined by full-matrix least squares (2 728 reflections to R 0.052, and 1 320 reflections to R 0.064, respectively). Both cations are six-co-ordinate with geometries best described as pentagonal pyramidal with the metal atom bonded to five nitrogen atoms of the macrocycle [Cd–N 2.428(7), 2.425(7), 2.335(7), 2.452(7), and 2.370(7); Hg–N 2.44(3), 2.25(5), 2.40(4), 2.44(5), and 2.40(3)Å] and to a bromine atom in an axial position [Cd–Br 2.582(1), Hg–Br 2.565(5)Å]. The remaining members of the two series of complexes are assigned similar six-co-ordinate structures on the basis of i.r. and electronic spectra together with electrical-conductance measurements in solution, with the exception of [CdL³(NCS)₂] which is seven-co-ordinate in the solid state. The structures are discussed in relation to those of metal complexes of related macrocyclic ligands.