Coordinative versatility of the carbonic anhydrase inhibitor benzolamide in zinc and copper model compounds

New benzolamide (H(2)bz, 5-phenylsulfonamide-1,3,4-thiadiazole-2-sulfonamide) zinc(II) and copper(II) complexes with tris(2-benzimidazolyl-methylamine) (L) and ammonia are reported. The crystal structures of the Zn(II) complexes were determined. The [Zn(Hbz)L]ClO4. H2O compound crystallizes in the triclinic Pi space group with a = 11.006(1), b = 14.777(2), c = 14.918(2) Angstrom, alpha = 114.30(1), beta = 98.90(1), gamma = 107.36(1)degrees and Z = 2. In this compound the Zn(II) has a distorted trigonal bipyramidal geometry. The {[Zn-2(bz)(2)(NH3)(4)]. 2H(2)O}(infinity) crystallizes in the monoclinic space group C2/c with a = 23.530(3), b = 10.4124(11), c = 15.428(2) Angstrom, beta = 110.591(9)degrees and Z = 4. The metal centre is in a distorted tetrahedral [ZnN4] environment. The benzolamide presents a different coordination behaviour in these complexes. In [Zn(Hbz)L]ClO4 . H2O it acts as a monodentate ligand through the thiadiazole N atom contiguous to the deprotonated sulfonamido group, while in {[Zn-2(bz)(2)(NH3)(4)]. 2H(2)O}(infinity) it behaves as a bridge joining two Zn(II) ions via the N atom of the thiadiazole ring and the N atom of the free sulfonamido group. The Cu(Hbz)L(NO3) complex was also obtained and characterized. The electronic properties and the EPR of the copper-doped zinc complexes showed that the copper(II) ion adopts a square pyramidal geometry. Also, for the Zn(II) complexes the interaction Zn-benzolamide has been studied using extended-Huckel molecular-orbital (EHMO) calculations. (C) 1999 Elsevier Science Inc. All rights reserved.