title: The role of the bridging group in exchange coupling in dinuclear homo- and heterometallic Ni(II) and Co(II) complexes with oxalate, oxamidate and dithiooxamidate bridges.
abstract: Six homodinuclear and two heteronuclear complexes Tp(Np)Co-C(2)O(4)-CoTp(Np) (1), Tp(Np)Co-C(2)O(4)-NiTp(Cy) (2), Tp(Cy)Ni-C(2)O(4)-NiTp(Cy) (3), Tp(Np)Co-C(2)O(2)(NH)(2)-CoTp(Np) (4), Tp(Cy)Ni-C(2)O(2)(NH)(2)-NiTp(Cy) (5), Tp(Np)Co-C(2)S(2)(NH)(2)-CoTp(Np) (6), Tp(Np)Co-C(2)S(2)(NH)(2)-NiTp(Cy) (7), Tp(Cy)Ni-C(2)S(2)(NH)(2)-NiTp(Cy) (8) (Tp(Np) = tris(3-neopentylpyrazolyl)borate, Tp(Cy) = tris(3-cyclohexylpyrazolyl)borate), were synthesized and characterized by mass spectrometry, electronic spectroscopy and X-ray crystallography. These compounds possess similar molecular structures, with the metal ions linked by bridging oxalate (1-3), oxamidate (4 and 5) or dithiooxamidate (6-8) ions. The heteronuclear nature of compounds 2 and 7 was additionally confirmed by high-resolution mass spectrometry. The magnetic properties of the Co(2+) complexes were modelled taking into account zero-field splitting of this ion, yielding D-values for Co(2+) in the range -17(1) to -50(1) cm(-1). All the metal ion pairs in compounds 1-8 are antiferromagnetically-coupled, with J values between -10.0(1) and -45.0(2) cm(-1) (via the exchange Hamiltonian Ĥ(ex.) = -2JŜ(1)Ŝ(2)) and |J| increasing in the order oxalate < oxamidate < dithiooxamidate. This tendency can be attributed to greater M-S bond covalency compared to M-N or M-O bonds (M = Co(2+) and Ni(2+)). It was found that this antiferromagnetic coupling of Co(2+) and Ni(2+) ions through oxalate is more efficient for these tris(pyrazolyl)borate complexes than for similar oxalate-bridged systems with neutral aliphatic amine ligands.
authors.affiliation: L. V. Pisarzhevskii Institute of Physical Chemistry of the National Academy of Sciences of the Ukraine, Prospekt Nauki 31, Kiev, 03028, Ukraine.
authors.forename: Elena A
authors.initials: EA
authors.lastname: Mikhalyova
authors.forename: Sergey V
authors.initials: SV
authors.lastname: Kolotilov
authors.forename: Olivier
authors.initials: O
authors.lastname: Cador
authors.forename: Matthias
authors.initials: M
authors.lastname: Zeller
authors.forename: Swiatoslaw
authors.initials: S
authors.lastname: Trofimenko
authors.forename: Lahcène
authors.initials: L
authors.lastname: Ouahab
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Addison
authors.forename: Vitaly V
authors.initials: VV
authors.lastname: Pavlishchuk
authors.forename: Allen D
authors.initials: AD
authors.lastname: Hunter
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008280:Magnetics; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D019815:Oxalic Acid / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D003035:Cobalt; D009532:Nickel; D019815:Oxalic Acid