Manganese(II) complexes containing the tridentate ligands 2,6-bis[1-(phenylimino)ethyl]pyridine, L1, or 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine, L2. The molecular structures of five-co-ordinate [MnBr2L1] and the zinc analogue [ZnCl2L1]

Abstract

Reactions of equimolar ratios of MnX₂·4H₂O (X = Cl or Br) and the tridentate ligands 2,6-bis [1-(phenylimino)ethyl]pyridine (L¹) or 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine (L²) afford the five-co-ordinate complexes [MnX₂L¹] and [MnX₂L²]. The complex [MnBr₂L¹], as the monobenzene solvate, crystallises in the space group P2₁2₁2₁ with a= 8.761(3), b= 17.032(5), c= 17.453(5)Å, and Z= 4. The distorted trigonal-bipyramidal geometry around manganese involves a trigonal plane with angles close to 120° comprising both bromines and the pyridyl nitrogen of L¹. However, strain induced by this ligand reduces the axial NMnN angle to 142.8°. The Mn–N(pyridyl) bond is markedly shorter than the axial Mn–N(imino) bonds. For comparison, the structure of [ZnCl₂L¹], as the 1.5MeCN solvate, has been determined. This complex crystallises in the triclinic space group P with a= 8.977(3), b= 12.585(5), c= 22.297(6), α= 90.99(3), β= 98.27(2), γ= 94.33(3)°, and Z= 4. The two independent molecules of [ZnCl₂L¹] in the asymmetric unit are geometrically identical within the limits of experimental error, with bond lengths and angles differing by less than twice the estimated standard deviations. The distorted trigonal-bipyramidal geometry and bond length and angle variations are similar to those of the manganese complex. Reactions of Mn(ClO₄)₂·6H₂O with 2 equivalents of L¹ or L² produce the cations [MnL¹₂]²⁺ and [MnL²₂]²⁺ isolated as the perchlorates. The two ligands of the octahedral cations are co-ordinated in a meridional manner.