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 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.