From compounds to materials: heterodinuclear complexes as precursors in the synthesis of mixed oxides; crystal structures of [Cu(H2LA)] and [{CuY(LA)(NO3)(dmso)}2]·2dmso [H4LA=N,N′-ethylenebis(3-hydroxysalicylideneimine), dmso = dimethyl sulphoxide]

Abstract

Mononuclear copper(II) and nickel(II) complexes [M(H₂L_A)] have been obtained by reaction of the appropriate metal acetate with the potentially hexadentate compartmental ligand H₄L_A, prepared by condensation of 2,3-dihydroxybenzaldehyde with ethylenediamine. Physicochemical data suggest the metal ion is in the inner N₂O₂ compartment. An X-ray investigation on [Cu(H₂L_A)] showed that the crystals are orthorhombic, space group Pnca, with a= 19.381(5), b= 15.327(4), c= 10.158(4)Å for Z= 8 and confirms the inner occupancy of copper(II) which exhibits an almost square-planar configuration. The bond lengths to Cu^II[Cu–N 1.93(1), Cu–O 1.89(1)Å(mean)] are within the usual range. The complexes [M(H₂L_A)] act as ligands in the formation of heterodinuclear [M¹M²L_A(X)(solv)_n](M¹= Cu or Ni, M²= La or Y, X = NO₃ or Cl) or [M¹M²L_A(solv)_n](M = Cu or Ni, M²= UO₂ or Ba) species [solv = H₂O, methanol or dimethyl sulphoxide (dmso)]. Crystals of [{CuY(L_A)(NO₃)(dmso)}₂]·2dmso, grown from dmso–MeOH are triclinic, space group P, with a= 9.919(5), b= 11.357(5), c= 13.789(6)Å for Z= 1 (the asymmetric unit is half of the molecule). The X-ray structure shows that the copper(II) is four-co-ordinated in the inner N₂O₂ compartment while the yttrium(III) is eight-co-ordinated in the outer O₂O₂. The complex is a tetranuclear asymmetric unit, two yttrium(III) ions being held together by phenolic oxygen bridges. The Y–O(ligand) bonds are in the range 2.28–2.40 Å, Y–O(dmso) is 2.31(1)Å and Y–O(nitrate) are 2.48 Å(mean). The Cu ⋯ Y and Y ⋯ Y distances are 3.397(3) and 3.781(2)Å respectively. The co-ordination of each yttrium(III) ion is completed by the oxygens of a bidentate nitrate ion and a dmso molecule. The geometry around the metal ion can be described as pentagonal bipyramidal. Two dmso molecules are present in the cell as clathrate solvent. The thermal decomposition of copper(II)–yttrium(III) and –lanthanum(III) complexes and the consequent formation of mixed oxides have also been studied and the preliminary results are reported.