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···Cl2M synthons A have been exploited in 1–4, 6, and 7. Both NH···Cl2M (sythons A) and B­(OH)2···Cl2M (sythons B) interactions give rise to a synthon of form I in 6. The uncommon folded conformation of the NH···Cl2M (synthons A) are formed in 7. The NH or OH donors and consequent branching of the NH···Cl hydrogen-bond network leads to one-, two-, and three-dimensional structures. These structures are further stabilized by CH···O and CH···Cl and π···π stacking interactions.