Chlorometallate-Pyridinium Boronic Acid Salts for Crystal Engineering: Synthesis of One-, Two-, and Three-Dimensional Hydrogen Bond Networks

A series of new crystal structures of salts containing 3- and 4-pyridineboronic acid (3- and 4-pba) with chlorometallate have been prepared: [4-pbaH][MnCl2] (1), [4-pbaH][CdCl2], (2), [4-pbaH]2[CuCl4] (3), [4-pbaH]2[PdCl4] (4), [3-pbaH](2)[CdCl4] (5), [3-pbaH][CuCl3(OH2)] (6), and [3-pbaH][PdCl2] (7). In these salts five structural forms for the chlorometallate species are observed: mononuclear square planar [M = Pd (4 and 7)], dimeric square-pyramidal [M = Cu (3)], polymeric square-pyramidal [M = Cu (6)], polymeric trans-edge-sharing octahedral [M = Mn (1), Cd (2)], and polymeric cis-edge-sharing octahedral [M = Cd (5)]. The cyclic R2,2(8) boronic acid dimer is formed in the salt of 1-5. NH center dot center dot center dot Cl2M synthons A have been exploited in 1-4, 6, and 7. Both NH...Cl2M (sythons A) and B(OH)2 center dot center dot center dot Cl2M (sythons B) interactions give rise to a synthon of form I in 6. The uncommon folded conformation of the NH center dot center dot center dot Cl2M (synthons A) are formed in 7. The NH or OH donors and consequent branching of the NH center dot center dot center dot Cl hydrogen-bond network leads to one-, two-, and three-dimensional structures. These structures are further stabilized by CH center dot center dot center dot O and CH center dot center dot center dot Cl and p center dot center dot center dot p stacking interactions.