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)](NO3)(nH(2)O). The metal in this compound can be replaced with isoelectronic Tl(l), affording TI[B(IM)(4)], and the borate can be modified by using 4-methylimidazole, resulting in Pb[B(4-Melm)(4)](NO3) and TI[B(4-Melm)(4)]. Like the parent Pb[B(Im)(4)](NO3)(nH(2)O), TI[B(Im)(4)] and TI[B(4-Melm)(4)] are layered network structures but both lack anions or solvent molecules in the interlayer spacing. The material Pb[B(4-Melm)(4)](NO3), 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 TI(l) 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 TI[B(4-Melm)(4)].