Theoretical study of the magnetic exchange coupling behavior substituting Cr(III) with Mo(III) in cyano‐bridged transition metal complexes

Molecular magnetism in a series of cyano‐bridged first and second transition metal complexes has been investigated using density functional theory (DFT) combined with the broken‐symmetry (BS) approach. Several exchange‐correlation (XC) functionals in the ADF package were used to investigate complexes I [−(Me 3 tacn) 2 (cyclam)NiMo 2 (CN) 6 ] 2+ , II [−(Me 3 tacn) 2 (cyclam)Ni‐Cr 2 (CN) 6 ] 2+ , III [(Me 3 tacn) 6 MnMo 6 (CN) 18 ] 2+ , and IV [(Me 3 tacn) 6 MnCr 6 (CN) 18 ] 2+ (Me 3 tacn = N,N′,N‴ ‐trimethyl‐1,4,7‐triazacyclononane). For models A (the molded structure of complex I) and B (the modeled structure of complex II), all the XCs given qualitatively reasonable results and predict ferromagnetic coupling character between M (M = Mo III for A or Cr III for B) and Ni II in coincidence with the experimental results (see Tables I and II). The calculated using Operdew, OPBE, O3LYP, and B3LYP functionals and experimental J values show that substituting Cr III with Mo III will enhance the ferromagnetic exchange coupling interactions. But VWN, PW91, PBE, VSXC, and tau‐HCTH functionals have no way to differentiate the relative strength of the intramolecular magnetic exchange coupling interactions of A and B correctly. For models C (the modeled structure of complex III) and D (the modeled structure of complex IV), all the XCs in ADF and B3LYP in Gaussian 03 with several basis sets show that substituting Cr III with Mo III will enhance the antiferromagnetic exchange coupling interactions. From the above calculations, the substitution of Cr III by Mo III will enhance the magnetic coupling interactions, whether the magnetic coupling interactions are ferro‐ or antiferromagnetic. Moreover, Kahn's model was applied to investigate the above facts. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006