Synthesis and coordination chemistry of two N_2-donor chelating di(indazolyl)methane ligands: Structural characterization and comparison of their metal chelation aptitudes

摘要

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 ~1and L~2with ZnX_2(X = Cl, Br, or I) yields [ZnX_2L] species (1-6), that, in the solid state, show a tetrahedral structure with dihapto ligand coordination via the pyrazolyl arms. The reaction of L~1and L~2with Zn(NO_3)_2· 6H_2O is strongly dependent on the reaction conditions and on the ligand employed. Reaction of L~1with equimolar quantities of Zn(NO_3)_2·6H_2O yields the neutral six-coordinate species [Zn(NO_3)_2(L~1)], 7. On the other hand the use of L~1excess gives the 2:1 adduct [Zn(NO _3)_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~2with Zn(NO_3) _2·6H_2O which gives the ionic [Zn(NO _3)(L~2)_2](NO_3), 10. Complete displacement of both nitrates from the zinc coordination sphere is observed when the reaction between L~1excess and the zinc salt was carried out in hydrothermal conditions. The metal ion type is also determining structure and stoichiometry: the reaction of L~2with CdCl_2gave the 2:1 adduct [CdCl_2(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~1with CdBr_2the polynuclear [CdBr_2(L~1)]_n12 is obtained, the Br~-anion acting as bridging ligands in a six-coordinate cadmium coordination environment. The reaction of L~1and L~2with HgX_2(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 = L~1, 16, 17: L = L~1or 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.