Systematic Study of Spin Crossover and Structure in [Co(terpyRX)2](Y)2 Systems (terpyRX = 4′-alkoxy-2,2′:6′,2′′-terpyridine, X = 4, 8, 12, Y = BF4, ClO4, PF6, BPh4)

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Institute of Physics and Chemistry, University of Southern Denmark, Odense, Denmark
School of Physics
§ School of Chemistry
Monash University, Clayton, Victoria 3800, Australia
Centre for Magnetic Resonance
School of Chemistry and Molecular Biosciences
University of Queensland, St. Lucia, Queensland 4072, Australia
*To whom correspondence should be addressed. E-mail: [email protected]. Tel: +61-3-99054512. Fax: +61-3-99054597. E-mail: [email protected]. Fax: +45 6615 8780. Tel: +45 6550 2543.
Cite this: Inorg. Chem. 2009, 48, 15, 7033–7047
Publication Date (Web):July 2, 2009
Copyright © 2009 American Chemical Society
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A family of spin crossover cobalt(II) complexes of the type [Co(terpyRX)2](Y)2·nH2O (X = 4, 8, 12 and Y = BF4, ClO4, PF6, BPh4) has been synthesized, whereby the alkyl chain length, RX, and counteranion, Y, have been systematically varied. The structural (single crystal X-ray diffraction) and electronic (magnetic susceptibility, electron paramagnetic resonance (EPR)) properties have been investigated within this family of compounds. Single crystal X-ray diffraction analysis of [Co(terpyR8)2](ClO4)2, [Co(terpyR8)2](BF4)2·H2O, and [Co(terpyR4)2](PF6)2·3H2O, at 123 K, revealed compressed octahedral low spin Co(II) environments and showed varying extents of disorder in the alkyl tail portions of the terpyRX ligands. The magnetic and EPR studies were focused on the BF4 family and, for polycrystalline solid samples, revealed that the spin transition onset temperature (from low to high spin) decreased as the alkyl chain lengthened. EPR studies of polycrystalline powder samples confirmed these results, showing signals only due to the low spin state at the temperatures seen in magnetic measurements. Further to this, simultaneous simulation of the EPR spectra of frozen solutions of [Co(terpyR8)2](BF4)2·H2O, recorded at S-, X-, and Q-band frequencies, allowed accurate determination of the g and A values of the low spin ground state. The temperature dependence of the polycrystalline powder EPR spectra of this and the R4 and R12 complexes is explained in terms of Jahn−Teller effects using the warped Mexican hat potential energy surface model perturbed by the low symmetry of the ligands. While well recognized in Cu(II) systems, this is one of the few times this approach has been used for Co(II).

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Tables and Figures of crystallographic data (Tables S1−S4, Figures S1−S6); table of IR and Raman band positions (Table S5); EPR of frozen solutions (Figure S7), EPR intensity plots (Figures S8−S11), and figures of magnetic moments vs temperature for complexes with other anions (Figures S12−S20). This material is available free of charge via the Internet at

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