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Syntheses, structural, magnetic, and electron paramagnetic resonance studies of monobridged cyanide and azide dinuclear copper(II) complexes : antiferromagnetic superexchange interactions.
Autorzy
Rok wydania
2015
Czasopismo
Numer woluminu
54
Strony
1487-1500
DOI
10.1021/ic502485p
Kolekcja
Język
Angielski
Typ publikacji
Artykuł
The reactions of Cu(ClO4)2 with NaCN and the ditopic ligands m-bis[bis(1-pyrazolyl)methyl]benzene (Lm) or m-bis[bis(3,5-dimethyl-1-pyrazolyl)methyl]benzene (Lm*) yield [Cu2(μ-CN)(μ-Lm)2](ClO4)3 (1) and [Cu2(μ-CN)(μ-Lm*)2](ClO4)3 (3). In both, the cyanide ligand is linearly bridged (μ-1,2) leading to a separation of the two copper(II) ions of ca. 5 Å. The geometry around copper(II) in these complexes is distorted trigonal bipyramidal with the cyanide group in an equatorial position. The reaction of [Cu2(μ-F)(μ-Lm)2](ClO4)3 and (CH3)3SiN3 yields [Cu2(μ-N3)(μ-Lm)2](ClO4)3 (2), where the azide adopts end-on (μ-1,1) coordination with a Cu–N–Cu angle of 138.0° and a distorted square pyramidal geometry about the copper(II) ions. Similar chemistry in the more sterically hindered Lm* system yielded only the coordination polymer [Cu2(μ-Lm*)(μ-N3)2(N3)2]. Attempts to prepare a dinuclear complex with a bridging iodide yield the copper(I) complex [Cu5(μ-I4)(μ-Lm*)2]I3. The complexes 1 and 3 show strong antiferromagnetic coupling, −J = 135 and 161 cm–1, respectively. Electron paramagnetic resonance (EPR) studies coupled with density functional theory (DFT) calculations show that the exchange interaction is transmitted through the dz2 and the bridging ligand s and px orbitals. High field EPR studies confirmed the dz2 ground state of the copper(II) ions. Single-crystal high-field EPR has been able to definitively show that the signs of D and E are positive. The zero-field splitting is dominated by the anisotropic exchange interactions. Complex 2 has −J = 223 cm–1 and DFT calculations indicate a predominantly dx2–y2 ground state.
Adres publiczny
http://dx.doi.org/10.1021/ic502485p
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