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Dinuclear metallacycles with single M—X—M bridges (X = Cl-, Br- ; M = Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)) : strong antiferromagnetic superexchange interactions.
Autorzy
Rok wydania
2017
Czasopismo
Numer woluminu
56
Strony
2884-2901
DOI
10.1021/acs.inorgchem.6b02933
Kolekcja
Język
Angielski
Typ publikacji
Artykuł
A series of monochloride-bridged, dinuclear metallacycles of the general formula [M2(μ-Cl)(μ-L)2](ClO4)3
have been prepared using the third-generation, ditopic bis-(pyrazolyl)methane ligands L = m-bis[bis(1-pyrazolyl)methyl]-
benzene (Lm), M = Cu(II), Zn(II), and L = m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*), M = Fe(II), Co-
(II), Ni(II), Cu(II), Zn(II), Cd(II). These complexes were synthesized from the direct reactions of M(ClO4)2·6H2O, MCl2,
and the ligand, Lm or Lm*, in the appropriate stoichiometric amounts. Three analogous complexes of the formula [M2(μ-
Cl)(μ-L)2](BF4)3, L = Lm, M = Cu(II), and L = Lm*, M = Co(II), Cu(II), were prepared from the reaction of
[M2(μ-F)(μ-L)2](BF4)3 and (CH3)3SiCl. The bromide-bridged complex
[Cu2(μ-Br)(μ-Lm*)2](ClO4)3 was prepared by the first method. Three acyclic complexes, [Co2(μ-Lm)μ-Cl4], [Co2(μ-Lm*)Cl4],
and [Co2(μ-Lm*)Br4], were also prepared. The structures of all [M2(μ-X)(μ-L)2]3+ (X = Cl−, Br−) complexes have two ditopic
bis(pyrazolyl)methane ligands bridging two metals in a metallacyclic arrangement. The fifth coordination site of the distorted
trigonal bipyramidal metal centers is filled by a bridging halide ligand that has an unusual linear or nearly linear M−X−M angle.
The NMR spectra of [Zn2(μ-Cl)(μ-Lm*)2](ClO4)3 and especially [Cd2(μ-Cl)(μ-Lm*)2](ClO4)3 demonstrate that the
metallacycle structure is maintained in solution. Solid state magnetic susceptibility data for the copper(II) compounds show
very strong antiferromagnetic exchange interactions, with −J values of 536 cm−1 for [Cu2(μ-Cl)(μ-Lm)2](ClO4)3·xCH3CN, 720
cm−1 for [Cu2(μ-Cl)(μ-Lm*)2](ClO4)3, and 945 cm−1 for [Cu2(μ-Br)(μ-Lm*)2](ClO4)3·2CH3CN. Smaller but still substantial
antiferromagnetic interactions are observed with other first row transition metals, with −J values of 98 cm−1 for [Ni2(μ-Cl)(μ-
Lm*)2](ClO4)3, 55 cm−1 for [Co2(μ-Cl)(μ-Lm*)2](ClO4)3, and 34 cm−1 for [Fe2(μ-Cl)(μ-Lm*)2](ClO4)3. EPR spectra of
[Cu2(μ-Cl)(μ-Lm*)2](BF4)3 confirm the dz2 ground state of copper(II). In addition, the sign of the zero-field splitting parameter
D was determined to be positive for [Cu2(μ-F)(μ-Lm*)2](BF4)3. Electronic spectra of the copper(II) complexes as well as
Mössbauer spectra of the iron(II) complexes were also studied in relation with the EPR spectra and magnetic properties,
respectively. Density functional theory calculations were performed using ORCA, and exchange integral values were obtained
that parallel but are slightly higher than the experimental values by about 30%.
Adres publiczny
http://dx.doi.org/10.1021/acs.inorgchem.6b02933
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