Mercury(II)–methylene blue interactions: Complexation and metallate formation

Abstract

Reactions of HgX 2 (X = Cl, Br, I) with methylene blue (MB) chloride dihydrate and the reaction of HgCl 2 with MB nitrate dihydrate have been undertaken in an attempt to prepare metal derivatives of MB. The products were characterized by elemental analysis, UV–Vis, IR, 1H NMR spectroscopy and X-ray crystallography. The reaction of HgCl 2 with MB chloride dihydrate and subsequent crystallization in a DMF/H 2O mixture yielded the products ( 1 and 2) with different crystal morphologies. The structure of complex 1 represents the first structural report of a complex of MB with any metal ion. The efficacy of MB to act as a ligand in spite of its cationic nature is thus demonstrated. The structure of 1 comprises a distorted tetrahedral geometry around Hg(II); the coordination valencies being provided by three chloride ions and a MB cation. The structure of 2 is a salt consisting of an HgCl 4 2 - anion and two MB cations. The reaction of HgI 2 and HgBr 2 with MB chloride dihydrate yielded salts 3 and 4 with Hg 2 X 6 2 - (X = Br or I) anions and MB cations. A mixed salt 5, whose anions comprise mercury(II), chloride and nitrate species resulted from the reaction between HgCl 2 with MB nitrate dihydrate. The reaction of Hg 2F 2 with MB chloride dihydrate and the crystallization of the resulting product 6 in aqueous DMF yielded crystals of (MB) 2HgCl 4 · H 2O.