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

The coordination polymer PbB(Im)(4)](NO(3))(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 (207)Pb solid state NMR (SSNMR) and thermogravimetric analysis (TGA). Stoichiometric exchange of (15)N nitrate for nitrate and iodide for nitrate is monitored by (15)N and (207)Pb SSNMR, and single crystals of the iodide-exchanged material PbB(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 PbB(Im)(4)](C(6)H(5)COO)(0.5H(2)O). The ion exchange versus self-assembly behavior correlates with the structural differences in the three compounds. In both PbB(Im)(4)]I and PbB(Im)(4)](C(6)H(5)COO)(0.5H(2)O), the lead sites act as Lewis acids for the iodide and benzoate, respectively.