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Issue 4, 2011
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Synthesis, characterisation and magnetic properties of octahedral chromium(III) compounds with six C-donor ligands

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Abstract

The homoleptic, square pyramidal organochromium(III) compound [NBu4]2[Cr(C6F5)5] (1) reacts with excess organic isocyanides, CNR [R = tBu, 2,6-dimethylphenyl (Xy)], under dissociation of the apical C6F5 ligand to give the more saturated, singly charged complexes [NBu4][trans-Cr(C6F5)4(CNR)2] [R = tBu (2), Xy (3)], containing six monodentate C-donor ligands. These compounds exhibit an axially distorted octahedral structure (single-crystal X-ray diffraction) with the four C6F5 groups defining the equatorial positions and the CNR ligands occupying the axial ones. Compounds 2 and 3 both behave as spin quartet species (S = 3/2) at microscopic level (EPR spectroscopy), their macroscopic magnetic properties depending upon the nature of the terminal R group, as established by magnetisation measurements. When the R substituent is the saturated alkyl grouptBu, the compound (2) behaves as a simple paramagnet, with no magnetic interaction between individual CrIII centres along the whole temperature range measured (1.8–265 K). By contrast, a weak antiferromagnetic interaction is detected for compound 3 at low temperature with TN = 0.19(1) K. Since the closest intermetallic distances are similar in the crystals of 2·CH2Cl2 and 3·1.75CH2Cl2 (ca. 1.1 nm), we conclude that the insaturation of the aromatic Xy group together with the extended intermolecular π–π stacking interactions between Xy rings observed in the crystal lattice of 3·1.75CH2Cl2 (centroid-to-centroid distance: 0.35 nm) favour magnetic interaction between the individual magnetic centres.

Graphical abstract: Synthesis, characterisation and magnetic properties of octahedral chromium(iii) compounds with six C-donor ligands

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Publication details

The article was received on 21 Jul 2010, accepted on 29 Oct 2010 and first published on 13 Dec 2010


Article type: Paper
DOI: 10.1039/C0DT00891E
Citation: Dalton Trans., 2011,40, 853-861
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    Synthesis, characterisation and magnetic properties of octahedral chromium(III) compounds with six C-donor ligands

    P. J. Alonso, A. B. Arauzo, M. A. García-Monforte, I. García-Rubio, A. Martín, B. Menjón and C. Rillo, Dalton Trans., 2011, 40, 853
    DOI: 10.1039/C0DT00891E

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