LAUSR

Abstract Two novel compounds, {[Cr(pyim)(ox)2]2Mn}n·2nCH3OH (1) and {[Cr(pyim)(ox)2]2Co(H2O)2}·7.5H2O (2) [pyim = 2-(2′-pyridyl)imidazole and H2ox = oxalic acid], were synthesized by using the mononuclear chromium(III) complex PPh4[Cr(pyim)(ox)2]·H2O (PPh4+ = tetraphenylphosphonium) as metalloligand towards the fully solvated manganese(II) (1) and cobalt(II) (2) ions as perchlorate salts. The structure of 1 consists of neutral double chains, with diamond-shaped units sharing the manganese(II) ions with the two other corners being occupied by the chromium(III) ions. The two metal centres in 1 are connected by bis-bidentate oxalate groups, each [CrIII(pyim)(ox)2]− unit being bound to two manganese(II) ions through its two oxalate ligands. Complex 2 is a centrosymmetric trinuclear compound where two outer [CrIII(pyim)(ox)2]− units act as bidentate ligands through one of their two oxalate groups towards the inner trans-diaquacobalt(II) entity. The values of the chromium(III)–manganese(II) (1) and chromium(III)–cobalt(II) (2) separation across the oxalate bridge are 5.5233(14) [Cr(1)…Mn(1)], 5.5735(14) [Cr(1)…Mn(1b)] and 5.3681(11) A [Cr1⋯Co(1)]. The investigation of the magnetic properties of 1 and 2 in the temperature range 1.9–300 K reveals the occurrence of significant ferromagnetic interactions between the chromium(III) and the high-spin manganese(II) (1)/cobalt(II) (2) across the oxalate bridge. Monte Carlo simulations were used to evaluate the intrachain magnetic interaction in 1. Simple molecular orbital analysis of the exchange interactions in 1 and 2 identify the σ- and π-type pathways involving the d(x2 − y2) (Mn and Co)/d(xy) (Cr) and d(xz) (Cr)/d(yz) (Mn and Co) pairs of orthogonal magnetic orbitals as the main individual contributions accounting for the overall ferromagnetic couplings in these compounds.