An atropisomeric chiral 2,2'-bipyridyl-3,3'-dicarboxylic acid and corresponding platinum (II) complex

Abstract

2,2'-Bipyridyl-3,3'-dicarboxylic acid $(H_2BDC)$ spontaneously resolves on crystallization from water, giving monohydrated crystals of the space group $P2_12_12_1$. In any individual crystal, all the atropisomeric-skewed molecules are of one hand; however, on dissolution in water, optical activity is lost. Strong hydrogen bonding leads to a helical structure, via O-H...N links, and 3 further strong bonds between water and carboxylate groups produce a framework structure. The $pK_a$ values measured for $H_2BDC$ (3.18 ± 0.04 and 4.59 ± 0.02 at 20 ± 1 °C, in dilute aqueous solution) agree with the zwitterionic form. The reaction of $H_2BDC$ with potassium tetrachloroplatinate(II) in water gives $Pt(H_2BDC)Cl_2-H_2O$. The complex was characterized by elemental analysis and spectroscopic techniques.