Bimetallic compounds of trans-cyclohexane-1,2-diamine-NNN′N′-tetra-acetate (cdta). Part 3. Structural and magnetic characterization of the dinuclear [M(OH2)5][M′(cdta)]·H2O (M,M′= Ni,Ni; Mn,Ni; Mn,Cu; Co,Ni; or Co,Cu) and the tetranuclear [M(OH2)4][M′(cdta)(OH2)]·4H2O (M,M′= Zn,Zn; Zn–Co; Co,Co; or Mn,Co) complexes

Abstract

The crystal structures of the complexes [Co(OH₂)₅][Cu(cdta)]·H₂O (5), [Zn(OH₂)₄][Zn(cdta)(OH₂)]·4H₂O (6), and [Zn_0.7Co_0.3(OH₂)₄][Zn_0.3Co_0.7(cdta)(OH₂)]·4H₂O (7)(cdta =trans-cyclohexane-1,2-diamine-NNN′N′-tetra-acetate) have been determined by X-ray methods. They crystallize in space groups Pbc2₁, P2₁/n, and P2₁/n respectively. The respective unit-cell constants are: a= 10.878(5), 9.702(2), 9.731(9)Å; b= 11.757(5), 11.757(2), 11.783(2)Å; c= 17.446(14), 20.980(5), 21.031(9)Åβ= 90,95.61(2), 95.40(6)°. The Z value is 4 for all three compounds. The structures were solved by direct methods and refined to final respective R values of 0.056, 0.098, and 0.041. The structure of (5) consists of dinuclear entities, constructed from cationic [Co(OH₂)₅]²⁺ and anionic [Cu(cdta)]^2– molecules which are linked through a bridging carboxylate group from the cdta ligand. In (6) and (7), the species [M(2)(OH₂)₄]²⁺ and [M(1)(cdta)(OH₂)]^2–[M(1), M (2)= Zn,Co], sharing two oxygen atoms from different carboxylate groups, alternate in order to form tetranuclear entities. Magnetic properties in the range 1–100 K of compound (5) and those of the derivatives [Ni(OH₂)₅][Ni(cdta)]·H₂O (1), [Mn(OH₂)₅][Ni(cdta)]·H₂O (2), [Mn(OH₂)₅][Cu(cdta)·H₂O(3)], [Co(OH₂)₅][Ni(cdta)]·H₂O (4), [Co(OH₂)₄][Co(cdta)(OH₂)]·4H₂O (8), and [Mn(OH₂)₄][Co(cdta)(OH₂)]·4H₂O (9) are discussed by assuming a Heisenberg or lsing exchange coupling between the two metal ions with distinct Landé factors and local distortion parameters. All the compounds show antiferromagnetic behaviour at low temperatures, with exchange coupling parameters ranging from –0.8 [(5)] to –8.8 cm^–1[(4)].