Lead Tetrakis(imidazolyl)borate Solids: Anion Exchange, Solvent Intercalation, and Self Assembly of an Organic Anion

The coordination polymer Pb[B(Im)4](NO3)(xH2O), 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 207Pb
solid state NMR (SSNMR) and thermogravimetric analysis (TGA). Stoichiometric exchange of 15N nitrate for nitrate
and iodide for nitrate is monitored by 15N and 207Pb 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)(0.5H2O). 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)(0.5H2O), the lead sites act as Lewis acids for the iodide and benzoate, respectively.

以四(咪唑基)硼酸钠与硝酸铅(II)溶液为原料构筑的配位聚合物Pb[B(Im)4](NO3)(xH2O)属于层状材料，其金属中心朝向层间距。与天然层状矿物类似，该化合物在固态下可顺利发生阴离子交换与溶剂水可逆插层，且过程中保持结晶度。我们通过207Pb固态核磁共振(SSNMR)与热重分析(TGA)观测到了溶剂插层过程的变化。通过15N与207Pb SSNMR可监测硝酸根被15N标记硝酸根、碘离子取代硝酸根的化学计量交换过程，且成功分离得到碘离子交换后的材料Pb[B(Im)4]I的单晶。尽管碘化物可通过母体硝酸化合物的简易交换反应制得，但在自组装条件下，有机阴离子苯甲酸根会取代层间的硝酸根，在Pb[B(Im)4](C6H5COO)(0.5H2O)中形成交替单层结构。离子交换与自组装的行为差异与这三种化合物的结构差异相关。在Pb[B(Im)4]I与Pb[B(Im)4](C6H5COO)(0.5H2O)中，铅位点分别作为碘离子与苯甲酸根的路易斯酸位点。