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

Five new complexes of formula K-4[Pd-2(mpba)(2)] . 4H(2)O (1), {[K-4(H2O)(dmso)][Pd-2(mpba)(2)]} (2), {[Cu(bpca)](4)[Pd-2(mpba)(2)]} . 6H(2)O (3), {[Cu(bpca)](2)[Pd(opba)]} . 1.75dmso . 0.25H(2)O (4), {[Cu(bpca)](2)[Pd(opba)]}(n) . ndmso (5) [H(4)mpba =1,3-phenylenebis(oxamic acid), H(4)opba = 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 [Pd-2(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 [Pd-2(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 Cu-II-Pd-II-Cu-II 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 Cu-II-Pd-II-Cu-II 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 1.9300 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.