One-dimensional ferromagnetically coupled bimetallic chains constructed with trans-[Ru(acac)2(CN)2]-: Syntheses, structures, magnetic properties, and density functional theoretical study

Abstract

Four cyano-bridged 1D bimetallic polymers have been prepared by using the paramagnetic building block trans-[Ru(acac)2(CN)2](Hacac= acetylacetone): {[{Ni(tren)}{Ru(acac)2(CN)2}][ClO 4].CH3OH}n (1) (tren = tris(2-aminoethyl)amine) , {[{Ni(cyclen)}{Ru(acac)2(CN)2)][ClO4]. CH3OH)n (2) (cyclen = 1,4,7,10-tetraazacyclododecane), {[{Fe(salen)}{Ru(acac)2(CN)2}]}n., (3) (salen2- = N,N'bis(salicylidene)-o-ethyldiamine dianion) and [{Mn(5,5'-Me2salen)}2{Ru(acac)2(CN)2}][Ru(acac) 2(CN)2]. 2CH3OH (4) (5.5'-Me 2salen=N,N'bis(5,5'-dimethylsalicylidene)-o-ethylenediimine). Compounds 1 and 2 are 1D, zigzagged NiRu chains that exhibit ferromagnetic coupling between NiII and RuIII ions through cyano bridges with J= + 1.92 cnr-1, zJ' =-1.37 cm-1, g=2.20 for 1 and J= + 0.85 cm-1, zJ' = -0.16 cm-1, g=2.24 for 2. Compound 3 has a 1D linear chain structure that exhibits intrachain ferromagnetic coupling (J=.+ 0.62 cm-1, zJ' = -0.09 cm-1, g=2.08), but antiferromagnetic coupling occurs between FeRu chains, leading to metamagnetic behavior with TN = 2.6 K. In compound 4, two MnIII ions are coordinated to trans-[Ru(acac)2(CN)2]- to form trinuclear Mn2Ru units, which are linked together by Jt-Jt stacking and weak Mn...O* interactions to form a 1D chain. Compound 4 shows slow magnetic relaxation below 3.0K with φ=0.25, characteristic of superparamagnetic behavior. The MnIII...RuIII coupling constant (through cyano bridges) and the MnIII...MnIII coupling constant (between the trimers) are +0.87 and +0.24 cm-1, respectively. Compound 4 is a novel single-chain magnet built from Mn 2Ru trimers through noncovalent interactions. Density functional theory (DFT) combined with the broken symmetry state method was used to calculate the molecular magnetic orbitais and the magnetic exchange interactions between RuIII and M (M = NiII, FeIII, and Mn III) ions. To explain the somewhat unexpected ferromagnetic coupling between low-spin RuIII and high-spin FeIII and Mn III ions in compounds 3 and 4, respectively, it is proposed that apart from the relative symmetries, the relative energies of the magnetic orbitais may also be important in determining the overall magnetic coupling in these bimetallic assemblies. © 2010 Wiley-VCH. Verlag GmbH & Co. KGaA,.