Crystal structures of 1,1'-bis-(carb-oxy-meth-yl)-4,4'-bipyridinium derivatives.

The crystal structures of 2-[1'-(carb-oxy-meth-yl)-4,4'-bi-pyridine-1,1'-diium-1-yl]acetate tetra-fluoro-borate, C 14 H 13 N 2 O 4 + ·BF 4 - or (Hbcbpy)(BF 4 ), and neutral 1,1'-bis-(carboxyl-atometh-yl)-4,4'-bi-pyridine-1,1'-diium (bcbpy), C 14 H 20 N 2 O 8 , are reported. The asymmetric unit of the (Hbcbpy)(BF 4 ) consists of a Hbcbpy + monocation, a BF 4 - anion, and one-half of a water mol-ecule. The BF 4 - anion is disordered. Two pyridinium rings of the Hbcbpy + monocation are twisted at a torsion angle of 30.3 (2)° with respect to each other. The Hbcbpy monocation contains a carb-oxy-lic acid group and a deprotonated carboxyl-ate group. Both groups exhibit both a long and a short C-O bond. The cations are linked by inter-molecular hydrogen-bonding inter-actions between the carb-oxy-lic acid and the deprotonated carboxyl-ate group to give one-dimensional zigzag chains. The asymmetric unit of the neutral bcbpy consists of one-half of the bcbpy and two water mol-ecules. In contrast to the Hbcbpy + monocation, the neutral bcbpy mol-ecule contains two pyridinium rings that are coplanar with each other and a carboxyl-ate group with similar C-O bond lengths. The mol-ecules are connected by inter-molecular hydrogen-bonding inter-actions between water mol-ecules and carboxyl-ate groups, forming a three-dimensional hydrogen-bonding network.