Pyridinium boronic acid salts in crystal synthesis

A series of salts of pyridinium boronic acids: [HNC5H4B(OH)2-4]2[M(S2C2O2)2]·2H2O (M = Cu 1, Ni 2, Pd 3, Pt 4), [HNC5H4B(OH)2-4]2[Pt(O2C2O2)2] (5); [HNC5H4B(OH)2-3]2 [M(S2C2O2)2] (M = Cu 6, Ni 7, Pd 8, Pt 9) and [HNC5H4B(OH)2-3]2[Pt(O2C2O2)2] (10) have been prepared and characterized by X-ray diffraction methods. Salts 2, 3 and 4 are isostructural and isomorphous and contain hydrogen-bonded supermolecules of form [pyridinium]2[M(S2C2O2)2] linked by BOH⋯OB and B(OH)–water hydrogen bonds into a three-dimensional network. Anhydrous salt 5 has a different structure in which the ions are linked by R(2,2)8 B(OH)2⋯carboxylate and pyridinium⋯carboxylate interactions to form a planar hydrogen-bonded ribbon. Salts 6, 7, 8 and 10 are all isostructural and isomorphous and contain hydrogen-bonded supermolecules of form [pyridinium]2[M(S2C2O2)2] linked by B(OH)2⋯carboxylate synthons to form a stepped chain. These chains pack in layers superimposed so as to afford short metal⋯metal contacts of length 3.6–4 A between layers. The structure of 5 is isomorphous with that of salts 6–8 and 10 but with a different pattern of NH hydrogen bonding as a result of the different isomer of pyridinium boronic acid present.