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

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