Magnetic coupling in discrete cyano-bridged MnIII-FeIII motifs: Synthesis, crystal structure, magnetic properties and theoretical study

• Published in: Dalton transactions : an international journal of inorganic chemistry 2010, Vol.39 (20), p.5028-5038
• Main Authors: Visinescu, Diana, Toma, Luminita Marilena, Cano, Joan, Fabelo, Oscar, Ruiz-Pérez, Catalina, Labrador, Ana, Lloret, Francesc, Julve, Miguel
• Format: Article
• Language: English
• Subjects: Crystal structure; Cyano groups; Hydrogen bonds; Iron; Joining; Magnetic properties; Mathematical analysis; Orbitals
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/b926912f

The preparation, crystal structures and magnetic properties of the heterobimetallic complexes of formula [MnIII(n-MeOsalen)(H2O)([small mu ]-CN)FeIII(bpym)(CN)3][middle dot]mH2O with n = m = 3 (1) and n = 4 and m = 2 (2) [n-MeOsalen2- = N,N[prime or minute]-ethylenebis(n-methoxysalicylideneiminate) dianion and bpym = 2,2[prime or minute]-bipyrimidine] are reported. 1 and 2 are dinuclear neutral species where the cyano-bearing low-spin unit [FeIII(bpym)(CN)4]- acts as a monodentate ligand towards the [MnIII(SB)(solv)x]+ entity (SB = tetradentate Schiff-base) through one of its four cyano groups. Adjacent heterobimetallic units are interlinked through hydrogen bonds involving the coordinated water molecule of one dinuclear unit and the phenolate oxygen atoms of the neighbouring one to afford pairs of dimers with values of the interdimer MnMn distance of 4.925(20) (1) and 5.0508(25) A (2). The analysis of the magnetic data of 1 and 2 in the temperature range 1.9-300 K shows the coexistence of weak ferro- [J = +2.95 (1) and +3.88 cm-1 (2)] and antiferromagnetic interactions [j = -1.91 (1) and -0.70 cm-1 (2)] through the single cyano bridge and hydrogen bonds, respectively (the Hamiltonian being of the type H = J[SFe[middle dot]SMn + SFe[prime or minute][middle dot]SMn[prime or minute]] -jSMn[middle dot]SMn[prime or minute]). Theoretical calculations using methods based on density functional theory (DFT) have been used to substantiate the nature and magnitude of the magnetic coupling observed in 1 and 2 and also to analyze the dependence of the magnetic coupling on the structural parameters for the Fe-C-N-Mn skeleton. An extension of the calculations to selected examples of heterobimetallic FeIII-C-N-MnIII compounds with a different number of cyano groups on the low-spin iron(iii) precursor has been carried out allowing us to illustrate the influence of the symmetry of the magnetic orbital of the iron center on the magnetic coupling in this heterobimetallic unit.