Crystal structures of 1,1′-bis(carboxymethyl)-4,4′-bipyridinium derivatives

The crystal structures of 2-[1′-(carboxymethyl)-4,4′-bipyridine-1,1′-diium-1-yl]acetate tetrafluoroborate, C14H13N2O4+·BF4− or (Hbcbpy)(BF4), and neutral 1,1′-bis(carboxylatomethyl)-4,4′-bipyridine-1,1′-diium (bcbpy), C14H20N2O8, are reported. The asymmetric unit of the (Hbcbpy)(BF4) consists of a Hbcbpy+ monocation, a BF4− anion, and one-half of a water molecule. The BF4− 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 carboxylic acid group and a deprotonated carboxylate group. Both groups exhibit both a long and a short C—O bond. The cations are linked by intermolecular hydrogen-bonding interactions between the carboxylic acid and the deprotonated carboxylate group to give one-dimensional zigzag chains. The asymmetric unit of the neutral bcbpy consists of one-half of the bcbpy and two water molecules. In contrast to the Hbcbpy+ monocation, the neutral bcbpy molecule contains two pyridinium rings that are coplanar with each other and a carboxylate group with similar C—O bond lengths. The molecules are connected by intermolecular hydrogen-bonding interactions between water molecules and carboxylate groups, forming a three-dimensional hydrogen-bonding network.