The [Cu4OCl6(IMIDH)4] complex has been synthesized and its crystal structure and magnetic properties determined.
The compound crystallizes as a dark green solid in the orthorhombic system, space group P212121, with cell
constants a = 11.469(2) Å, b = 13.933(2) Å, c = 16.778(3) Å and four formula units per cell. The complex has
a tetrameric structure of four copper(II) ions connected to a central oxo group, in an approximately tetrahedral
arrangement. Copper coordination is completed by three μ2-chloride ions and an imidazole nitrogen atom, defining
a trigonal bipyramidal environment around each copper ion. A new Heisenberg exchange scheme has been
developed, considering the experimentally observed distortion of the Cu4 tetrahedron. The magnetic susceptibilities
measurements were interpreted by means of this model, in terms of three coupling constants, J = −7.65 cm-1,
J
S = 83.3 cm-1, and J
L = −58.8 cm-1, which show a linear correlation with the observed Cu−O−Cu angles.
Three types of tetrone radical anions in which two 1,4‐benzoquinone units are connected by ethano (1·−, 2·−), [2.2]paracyclophane (3·−, 4·−), and anthracene bridges (5·−, 6·−) have been studied by ESR and ENDOR spectroscopy. The displacement of the unpaired electron over the two π moieties in the [2.2]cyclophane radical anions 1·−−4·− and the marked difference between the first and second reduction potentials, ΔE = |E20 − E10| ≥ 0.20 V, are evidence for a substantial intramolecular electronic interaction between the two electrophores. Similar ΔE data for the syn‐ (3) and anti‐naphthalenophanes (4) indicate that most of the intramolecular electronic interaction takes place through the [2.2]paracyclophane bridge. When ion pairing is inhibited by complexation of the cation, the unpaired electron in 5·− and 6·− is also delocalized over the whole pentacenetetrone system at temperatures as low as 160 K.
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