Lead and thallium tetrakis(imidazolyl)borates: modifying structure by varying metal and anion.

We are using the coordinating anions tetrakis(imidazolyl)borate and tetrakis(4-methylimidazolyl)borate to construct new metal-organic framework structures. In this report, we are exploring materials similar in composition to the previously reported layered network structure Pb[B(Im)(4)](NO(3))(nH(2)O). The metal in this compound can be replaced with isoelectronic Tl(I), affording Tl[B(Im)(4)], and the borate can be modified by using 4-methylimidazole, resulting in Pb[B(4-MeIm)(4)](NO(3)) and Tl[B(4-MeIm)(4)]. Like the parent Pb[B(Im)(4)](NO(3))(nH(2)O), Tl[B(Im)(4)] and Tl[B(4-MeIm)(4)] are layered network structures but both lack anions or solvent molecules in the interlayer spacing. The material Pb[B(4-MeIm)(4)](NO(3)), however, exhibits a 3D network structure that lacks an open topology, resulting from the increased stereochemical activity (greater steric bulk toward other ligands) of the 4-methylimidazole ring. Both of the Tl(I) solids display longer M-N bonds than observed in the analogous Pb(II) compounds; these lengths account for the decreased effect of the stereochemical activity of the 4-methylimidazole ring in Tl[B(4-MeIm)(4)].