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Issue 4, 2012
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A square-pyramidal organochromium(V) compound

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The mononuclear, five-coordinate organochromium(V) compound [NBu4][CrO(C6F5)4] (1) has been obtained as a dark red solid in moderate yield by treatment of the homoleptic organochromium(III) derivative [NBu4]2[Cr(C6F5)5] with NO[BF4] in CH2Cl2 solution under an oxygen atmosphere. The CrV centre in the [CrO(C6F5)4] anion shows a square-pyramidal geometry with the four C6F5 groups in the basal positions and the oxo ligand in the apical one (X-ray). The short Cr–O distance (153.8(2) pm) suggests a high degree of triple bond character for the chromyl unit. The EPR spectrum of 1 in solution shows an isotropic signal with giso = 1.995(1) and a rich hyperfine structure due to coupling with the 53Cr isotope [aCr = 46.95(4) MHz] as well as with the ortho-F and meta-F substituents of the C6F5 rings [aF = 4.20(2) MHz and aF = 2.12(2) MHz] in keeping with the presence of non-interacting, fast tumbling, paramagnetic [CrO(C6F5)4] units (d1). In the solid state, however, both the microscopic (EPR) and macroscopic magnetic properties (isothermal magnetisation and thermal dependence of the magnetic susceptibility) suggest the existence of weak ferromagnetic interactions with TC = 0.20(2) K. Such magnetic interactions may probably be favoured by π interactions between C6F5 rings of neighbour [CrO(C6F5)4] units in the crystal.

Graphical abstract: A square-pyramidal organochromium(v) compound

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The article was received on 21 Jul 2011, accepted on 21 Oct 2011 and first published on 01 Dec 2011

Article type: Paper
DOI: 10.1039/C1DT11376C
Citation: Dalton Trans., 2012,41, 1297-1303
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    A square-pyramidal organochromium(V) compound

    M. A. García-Monforte, P. J. Alonso, A. B. Arauzo, A. Martín, B. Menjón and C. Rillo, Dalton Trans., 2012, 41, 1297
    DOI: 10.1039/C1DT11376C

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