Molecular interactions of zinc(II) cyclams with polycarboxylato ligands

Four new zinc(II) cyclams of the composition {Zn(L)(tp(2-)) center dot H2O}(n) (1), {Zn(L)(H(2)bta(2-)) center dot 2H(2)O}(n) (2), [Zn-2(L)(2) (ox(2-))] 2ClO(4) center dot 2DMF (3), and Zn(L)(H(2)btc(-))(2) center dot 2DMF (4), where L = cyclam, tp(2-) = 1,4-benzenedicarboxylate ion, H(2)bta(2-) = 1,2,4,5-benzenetetracarboxylate ion, ox(2-) = oxalate ion, DMF = N,N-dimethylformamide, and H(2)btc(-) = 1,3,5-benzenetricarboxylate ion, have been synthesized and structurally characterized by a combination of analytical, spectroscopic and crystallographic methods. The carboxylato ligands in the complexes 1-4 show strong coordination tendencies toward zinc(11) cyclams with hydrogen bonding interactions between the pre-organized N-H groups of the macrocycle and oxygen atoms of the carboxylato ligands. The macro-cycles in 1, 2, and 4 adopt trans-III configurations with the appropriate R,R,S,S arrangement of the four chiral nitrogen centers, respectively. However, the complex 3 shows an unusual cis V conformation with the R,R,R,R nitrogen configuration. The finding of strong interactions between the carboxylato ligands and the zinc(11) ions may provide additional knowledge for the improved design of receptor-targeted zinc(II) cyclams in anti-HIV agents. (c) 2004 Elsevier B.V. All rights reserved.