Chemistry of the binary mixture of 1,10-phenanthroline and zinc perchlorate hexahydrate in methanol and gas phase. Monohydroxo species and tricoordination of zinc and water clusters

ESIMS reveals that methanol solutions of 1:1, 1:2 and 1:3 mixtures of Zn(ClO4)2 · 6H2O and 1,10-phenanthroline (phen) generate [Zn(phen)(OH)]+, [Zn(phen)(H2O)4(OH)]+, [Zn(phen)2(H2O)(OH)]+and [Zn(phen)2(H2O)4(OH)]+ ions in the gas phase. DFT calculations at the B3LYP/LanL2DZ level show that zinc is planar tricoordinate in [Zn(phen)(OH)]+ and the cis configuration is more stable than the trans one for the hexacoordinate ion [Zn(phen)2(H2O)(OH)]+. DFT calculations also show that the [Zn(phen)(H2O)4(OH)]+ and [Zn(phen)2(H2O)4(OH)]+ ions are actually [Zn(phen)(H2O)(OH)]+ · 3H2O and [Zn(phen)2(H2O)(OH)]+ · 3H2O containing extended motifs of H-bonded water clusters. The aqua species corresponding to the monohydroxo ions are acidic. Their acid dissociations are modeled collectively by equilibrium (see below) where other ligands around Zn are not specified. An attempt is then made to estimate KaZn-OH22+⇆KaZn-OH++H+of various binary mixtures of Zn(ClO4)2 · 6H2O and phen in methanol from solution conductivity. In accordance with the above results, the aqueous solution of [Zn(phen)3](ClO4)2 · C2H5OH · H2O is found to be acidic.

The accompanied ESI mass spectrum of the 1:1 mixture of Zn(ClO4)2 · 6H2O and 1,10-phenanthroline (phen) in methanol reveals existence of tricoordinate [Zn(phen)(OH)]+, tetracoordinate [Zn(phen)(H2O)(OH)]+ · 3H2O and hexacoordinate [Zn(phen)2(H2O)(OH)]+ · 3H2O ions. The last two ions contain extended motifs of H-bonded water clusters. The aqueous solution of [Zn(phen)3](ClO4)2 · C2H5OH · H2O is found to be acidic.Figure optionsDownload as PowerPoint slide