6533b873fe1ef96bd12d4ba0

RESEARCH PRODUCT

Magneto‐Structural Study of an Oxamato‐Bridged Pd II Co II Chain: X‐ray Crystallographic Evidence of a Single‐Crystal‐to‐Single‐Crystal Phase Transition

subject

description

Two new mononuclear oxamato-containing palladium(II) complexes of formula K2[Pd(opba)]·2H2O (1) and (PPh4)2[Pd(opba)]·2H2O (2) and the heterodimetallic palladium(II)–cobalt(II) chain {[Co(H2O)2Pd(opba)]·dmso}n (3) [opba = 1,2-phenylenebis(oxamate), PPh4+ = tetraphenylphosphonium cation and dmso = dimethyl sulfoxide] have been prepared, and the structures of two of them (compounds 2 and 3) were determined by X-ray diffraction analysis of single crystals. The structure of 2 consists of discrete anions of [Pd(opba)2]2– and PPh4+ cations. Each PdII ion in 2 is surrounded by two oxamate nitrogen atoms and two carboxylate oxygen atoms in a square-planar surrounding. Compound 3 is a neutral chain with regular alternating PdII and CoII ions, the [Pd(opba)]2– entity acting as a bis(bidentate) ligand towards trans-diaquacobalt(II) fragments, and dmso molecules of crystallization. Compound 3 exhibits a single-crystal-to-single-crystal phase transition between monoclinic C2/c (α phase) and triclinic P (β phase) space groups. Within the α phase the dmso molecule of crystallization is disordered, but it becomes ordered below 215 K in the β phase. The ordering process of the dmso molecule is followed by a reduction in the unit cell volume. The magnetic properties of 3 are barely affected by the structural phase transition, and they indicate an important spin–orbit coupling of the high-spin octahedral CoII ion [α = 1.245, λ = –151 cm–1, Δ = 494 cm–1, the spin Hamiltonian being defined as H = –αλLS + Δ(Lz2–2/3) + βH(–αL + geS)] with an almost negligible intra- [through the diamagnetic square-planar PdII centre] and interchain antiferromagnetic interactions (θ = –0.32 K).