Synthesis and Coordination Chemistry of Two N2-Donor Chelating Di(indazolyl)methane Ligands: Structural Characterization and Comparison of Their Metal Chelation Aptitudes

Abstract

The N2-donor bidentate ligands di(1H-indazol-1-yl)methane (L1) and di(2H-indazol-2-yl)methane (L2) (L in general) have been synthesized, and their coordination behavior toward ZnII, CdII, and HgII salts has been studied. Reaction of L1 and L2 with ZnX2 (X = Cl, Br, or I) yields [ZnX2L] species (1−6), that, in the solid state, show a tetrahedral structure with dihapto ligand coordination via the pyrazolyl arms. The reaction of L1 and L2 with Zn(NO3)2·6H2O is strongly dependent on the reaction conditions and on the ligand employed. Reaction of L1 with equimolar quantities of Zn(NO3)2·6H2O yields the neutral six-coordinate species [Zn(NO3)2(L1)], 7. On the other hand the use of L1 excess gives the 2:1 adduct [Zn(NO3)2(L1)2], 8 where both nitrates act as a unidentate coordinating ligand. Analogous stoichiometry is found in the compound obtained from the reaction of L2 with Zn(NO3)2·6H2O which gives the ionic [Zn(NO3)(L2)2](NO3), 10. Complete displacement of both nitrates from the zinc coordination sphere is observed when the reaction between L1 excess and the zinc salt was carried out in hydrothermal conditions. The metal ion type is also determining structure and stoichiometry: the reaction of L2 with CdCl2 gave the 2:1 adduct [CdCl2(L2)2] 11 where both chlorides complete the coordination sphere of the six-coordinate cadmium center; on the other hand from the reaction of L1 with CdBr2 the polynuclear [CdBr2(L1)]n 12 is obtained, the Br− anion acting as bridging ligands in a six-coordinate cadmium coordination environment. The reaction of L1 and L2 with HgX2 (X = Cl, I, SCN) is also dependent on the reaction conditions and the nature of X, two different types of adducts being formed [HgX(L)] (14: L = L1, 16, 17: L = L1 or L2, X = I, 19: L = L2, X = SCN) and [HgX(L)2] (15: L = L2, X = Cl, 18: L = L1, X = SCN). The X-ray diffraction analyses of compounds 1, 2, 4, 5, 7, 8, 10−12, 14, 15, and 19 are also reported. The variations of the coordination geometry parameters in the complexes are compared and discussed.