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

Template condensation products of 1,5-diaminopentane and 1,6-diaminohexane with 2,6-diacetylpyridine on Pb(NCS)2 have been transmetallated with CoII and CuII 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 = NiII and FeII, 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)A 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.