Syntheses, structures, and magnetic properties of multinuclear complexes constructed with complexed ligands, [M(bpca)2]+ (M=Cr(III), Fe(III), Co(III); Hbpca=bis(2-pyridylcarbonyl)amine)

Two trinuclear complexes [Fe(II)(ClO4)2{M(III)(bpca)2}2](ClO4)2 (M=Co for 1 and Fe for 2) and three chain complexes catena-[Fe(II)(ClO4)2{M(III)(bpca)2}]ClO4 (M=Co for 3, Cr for 4, and Fe for 5) were synthesized and structures for all complexes and magnetic properties for 3–5 were investigated (Hbpca=bis(2-pyridylcarbonyl)amine). All of these complexes consist of {trans-Fe(II)(ClO4)2} unit(s) and cationic complexed ligands, {M(III)(bpca)2}+, in an alternate arrangement. In 3–5, perchlorate anions in the {trans-Fe(II)(ClO4)2} unit are bound to a high-spin Fe(II) ion with relatively short distances in the range from 2.131(3) to 2.157(3) Å. The cationic complex ligands in 1 and 2 act as a bidentate terminal ligand whereas in 3–5 they act as a bis-bidentate bridging ligand. In 3, very weak ferromagnetic interaction occurs between Fe(II) ions via the diamagnetic complexed ligand [Co(III)(bpca)2]+. In both 4 and 5 antiferromagnetic interactions occur between high-spin Fe(II) and Cr(III) ions in 4 and high-spin Fe(II) and low-spin Fe(III) ions in 5, respectively. Compound 5 shows ferrimagnetic behavior at low temperature. A plot of 1/χM versus T above 50 K for 4 and 5 obey the Curie–Weiss law with negative Weiss constants of θ=−12.5(4) K for 4 and −15.3(6) K for 5, respectively. The temperature dependence of χMT for 5 was further analyzed by the Seiden model from which the J value was estimated as −13.8(3) cm−1 (H=−J[SFe(II)i+SFe(II)i+1]·SFe(III)i).