Terpyridyl Groups Research Articles

Complex formation between oxalate and (2,2′:6′,2″-terpyridyl)copper(II) in dimethyl sulphoxide solution. Synthesis and crystal structures of mono- and di-nuclear complexes

The crystal and molecular structures of two new complexes [{Cu(terpy)(H2O)}2(ox)][{Cu(terpy)}2(ox)][ClO4]4·2H2O 1 and [Cu(terpy)(H2O)(ox)]·4H2O 2(terpy = 2,2′:6′,2″-terpyridine and ox = oxalate) have been determined by X-ray diffraction. Crystals of 1 are monoclinic, space group P21/c, with Z= 2, a= 13.443(2), b= 23.183(4), c= 12.394(1)A and β= 116.29(1)°, whereas those of 2 are triclinic, space group P, with Z= 2, a= 10.192(2), b= 12.319(2), c= 8.397(3)A, α= 86.65(3), β= 96.80(3) and γ= 106.14(1)°. The structure of 1 contains two different centrosymmetrical copper(II) dinuclear dicationic units, unco-ordinated perchlorate groups and lattice water. In both dinuclear units the terpyridyl group is terminal and the oxalate acts as an asymmetrical bis(chelating) bridge. However, the copper atom is five-co-ordinate in one dinuclear unit and six-co-ordinate in the other. The structure of 2 consists of neutral mononuclear [Cu(terpy)(H2O)(ox)] entities and unco-ordinated water molecules. The copper atom is in a six-co-ordinate, teragonally elongated, octahedral environment. The stability constants of the oxalato complexes of [Cu(terpy)]2+[equations (i)–(iii)][Cu(terpy)]2++ ox2–+ H+[graphic omitted][Cu(terpy)(Hox)]+(i) 2[Cu(terpy)]2++ ox2–[graphic omitted] [{Cu(terpy)}2(ox)]2+(ii)[Cu(terpy)]2++ ox2–[graphic omitted][Cu(terpy)(ox)](iii) were determined by potentiometry in dimethyl sulphoxide solution: log β111= 12.397(4), log β210= 10.621(6) and log β110= 7.394(2)(25 °C, 0.1 mol dm–3[NBu4][ClO4]). The co-ordination modes of oxalate in the CuIIL–ox2– system (L being tri- or bi-dentate N-donor ligands) are discussed in the light of available thermodynamic and structural parameters.

Investigation on the Rare Earth Terpyridyl System

The preparation of terpyridyl chelates of heavier rare earths of the type M (Terp) (NO3)3 ·n H2O(M = Tb — Yb and n = O —3) is described. The infrared studies of the solid chelates show the coordinated nature of both terpyridyl and nitrate groups. A spectrochemical series based on the shift of the “breathing” vibration of terpyridyl in the complexes is proposed.