Binucleating N6 24- and 26-membered macrocyclic ligands. Part 2. Transition-metal homo- and hetero-binuclear complexes: X-ray crystallographic structure determination of a lead–manganese heterobinuclear complex

Abstract

Template condensation products of 1,5-diaminopentane and 1,6-diaminohexane with 2,6-diacetylpyridine on Pb(NCS)₂ have been transmetallated with Co^II and Cu^II to yield homobinuclear complexes of the 24- and 26-membered macrocycles, L¹ and L² respectively. In the dicobalt(II) complex of the smaller macrocycle, L¹, a thermally populated spin equilibrium exists lying well to the low-spin side at 93 K. E.s.r. spectra indicate the complex has an equatorially compressed tetragonal geometry. The dicobalt(II) complex of the larger macrocycle, L², is effectively high-spin, down to 93 K. Dicopper(II) complexes of L¹ display a weak antiferromagnetic interaction, absent in analogous complexes of L². Heterobinuclear complexes [PbML¹(NCS)₂(MeCN)₂][ClO₄]₂ of the 24-membered macrocycle have been prepared for M = Ni^II and Fe^II, as confirmed by fast-atom bombardment (f.a.b.) mass spectra. An X-ray crystallographic structure determination on the heterobinuclear complex PbMnL¹(NCS)₄ reveals a Pb–Mn distance of 4.857(2)Å and confirms that the metal centres are bridged by two 1,3-µ–NCS–bridges, as inferred from i.r. spectroscopy for the other thiocyanato complexes studied. However, the X-ray structure shows that in this case the thiocyanate bridges present both S-donors to Pb and both N-donors to Mn.