Side-chain effect on the co-ordination behaviour of glycine derivatives toward copper(II), crystal structure of bis(µ-N-tritylglycinato-O)-bis[(2,2′-bipyridine)(N-tritylglycinato-O)copper(II)]

Abstract

N-Triphenylmethylglycine (tgly) reacts with Cu^II producing a violet compound of formula [Cu(tglyO)₂]·3H₂O whose electronic spectrum is characteristic of an essentially square-planar CuN₂O₂ chromophore. This compound readily reacts with 2,2′-bipyridine (bipy), and a blue complex of empirical formula Cu(tglyO)₂(bipy) was crystallized and its crystal structure determined. The crystals are triclinic, space group P, with cell parameters a= 10.098(1), b= 12.573(11), c= 16.979(3)Å, α= 93.11 (3), β= 102.70(1), γ= 99.99(2)°, Z= 1, and R= 0.053. The structure consists of discrete dimeric [{Cu(tglyO)₂(bipy)}₂] units with CuN₂O₃ chromophores. The metal atoms are bridged through two unidentate carboxyl groups. The tglyO anions act as simple carboxylate ligands with no nitrogen bonding. The co-ordination behaviour in the mixed complex may be explained by the discriminatory effect of bipy toward the second ligand, favouring oxygen-over nitrogen-donor ligands, and by the steric hindrance of the three phenyl rings which prevent direct metal co-ordination of the nitrogen atom.