New Metal Oxamates as Precursors of Low-Dimensional Heterobimetallics

The goal of this work was to synthesize new molecular bricks which could be used as precursors of heterobimetallic low-dimensional compounds. Along this line, four compounds have been synthesized and structurally characterized, namely (NBu₄)₂[Ni(Cl₂opba)] (1), (NBu₄)₂[Cu(Cl₂opba)] (2), (NBu₄)₅[Mn(Cl₂opba)(DMSO)₂] ₄ (3), and Cu(en)₂-[Mn(Cl₂opba)(H₂O)₂] ₂·2DMSO (4), with Cl₂opba = (4,5-dichloro-o-phenylene)bis(oxamato), NBu₄ = tetra-n-butylammonium, en = ethylenediamine, and DMSO = dimethyl sulfoxide. Compounds 1 and 2 are isostructural; they crystallize in the monoclinic system, space group C2/c, Z = 4, with a = 18.708(2) Å, b = 17.525(2) Å, c = 14.763(9) Å, and β= 92.03(4)° for 1 and a = 18.928(2) Å, b = 17.634(2) Å, c = 14.704(9) Å, and β= 92.38(3)° for 2. 3 crystallizes in the tetragonal system, space group P4̄2₁c, Z = 2, with a = 26.295(10) Å and c = 12.342(7) Å. The structure shows a random occupation of the metal site by Mn(III) and Mn(II) ions in 3/4 and 1/4 ratios, respectively. 4 crystallizes in the triclinic system, space group P1̄, Z= 1, with a = 7.066(7) Å, b = 11.844(1) Å, c = 14.292(5) Å, α = 105.64(2)°, β- 97.67(5)°, and γ = 102.13(3)°. The structure consists of Mn^IIICu^IIMn^III trinuclear species, with Cu-O-Mn bridges involving oxygen atoms of the oxamato groups already linked to the metal atom. The magnetic properties of compounds 1-4 have been investigated and quantitatively interpreted. For 3, this magnetic investigation has been performed on a single crystal, which allows us to determine unambiguously the sign of the axial zero-field splitting parameter for the Mn(III) ion. The potentialities of these new molecular bricks have been discussed.