Lead tetra kis(imidazolyl) borate solids: Anion exchange, solvent intercalation, and self assembly of an organic anion

The coordination polymer Pb[B(Im)(4)](NO3)(xH(2)O), constructed by using sodium tetrakis (imidazolyl)borate and lead-(II) nitrate solutions, is a layered material with the metal centers facing the interlayer spacing. As in naturally occurring layered minerals, this compound can readily undergo anion exchange and reversible intercalation of solvent water in the solid state with retention of crystallinity. We observed changes in solvent intercalation by Pb-207 solid state NMR (SSNMR) and thermogravimetric analysis (TGA). Stoichiometric exchange of N-15 nitrate for nitrate and iodide for nitrate is monitored by N-15 and Pb-207 SSNMR, and single crystals of the iodide-exchanged material Pb[B(Im)(4)]I were isolated. While the iodide compound can be obtained through facile exchange from the nitrate parent compound, the organic anion benzoate is placed in the interlayer spacing for nitrate under self-assembly conditions and forms an alternating monolayer in Pb[B(Im)(4)](C6H5COO)(0.5H(2)O). The ion exchange versus self-assembly behavior correlates with the structural differences in the three compounds. In both Pb[B(Im)(4)]I and Pb[B(Im)(4)](C6H5COO)(0.5H(2)O), the lead sites act as Lewis acids for the iodide and benzoate, respectively.