Palladium(II)–Copper(II) Assembling with Bis(2-pyridylcarbonyl)amidate and Bis(oxamate) Type Ligands

Five new complexes of formula K4[Pd2(mpba)2] · 4H2O (1), {[K4(H2O)(dmso)][Pd2(mpba)2]} (2), {[Cu(bpca)]4[Pd2(mpba)2]} · 6H2O (3), {[Cu(bpca)]2[Pd(opba)]} · 1.75dmso · 0.25H2O (4), {[Cu(bpca)]2[Pd(opba)]} n · ndmso (5) [H4mpba =1,3-phenylenebis(oxamic acid), H4opba = 1,2-phenylenebis(oxamic acid), Hbpca = bis(2-pyridylcarbonyl)amide, and dmso = dimethyl sulfoxide] have been prepared and investigated by infrared spectroscopy, thermal analysis, single crystal X-ray diffraction, and magnetic susceptibility techniques. The structure of 2 consists of a [Pd2(mpba)2]4– anionic entity in which the palladium(II) cations are coordinated by two mpba ligands resulting in a dipalladium(II) unit that acts as a ligand toward potassium(I) cations leading to a neutral three-dimensional network. Compound 3 is a neutral hexanuclear complex where the dinuclear [Pd2(mpba)2]4– unit adopts a tetrakis(bidentate) coordination mode toward four [Cu(bpca)]+ end-cap entities. This compound can be viewed as a “dimer of trimers” in which two CuII–PdII–CuII trinuclear units are connected by two mpba ligands. Compounds 4 and 5 have in common the presence of a [Pd(opba)]2– unit, which acts as a bis(bidentate) ligand toward two [Cu(bpca)]+ entities to afford neutral heterotrinuclear CuII–PdII–CuII motifs that are interlinked through weak double (4) and single (5) out-of-plane copper(II) to carbonyl(bpca)-oxygen atoms leading to uniform linear (4) and zigzag (5) chains of heterobimetallic trinuclear units. The investigation of the magnetic properties of 3–5 in the 1.9–300 K temperature range reveals the presence of very weak antiferromagnetic interactions between the copper(II) ions. The nature and magnitude of these magnetic interactions are discussed in terms of orbital symmetry considerations.