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Jenkins DM, Peters JC: Spin-state tuning at pseudotetrahedral d (7) ions: examining the structural and magnetic phenomena of four-coordinate [BP3] CoII-X systems. J Am Chem Soc. 2005 May 18;127(19):7148-65.
Electronic structure, spin-state, and geometrical relationships for a series of pseudotetrahedral Co (II) aryloxide, siloxide, arylthiolate, and silylthiolate complexes supported by the tris (phosphino) borate [BP (3)] ligands [PhBP (3)] and [PhBP (i)()(Pr)(3)] ([PhB (CH (2) PPh (2))(3)](-) and [PhB (CH (2) P (i)() Pr (2))(3)](-), respectively) are described. Standard (1) H NMR, optical, electrochemical, and solution magnetic data, in addition to low-temperature EPR and variable temperature SQUID magnetization data, are presented for the new cobalt (II) complexes [PhBP (3)] CoOSiPh (3) (2), [PhBP (3)] CoO (4-(t)() Bu-Ph) (3), [PhBP (3)] CoO (C (6) F (5)) (4), [PhBP (3)] CoSPh (5), [PhBP (3)] CoS (2,6-Me (2)-Ph) (6), [PhBP (3)] CoS (2,4,6-(i)() Pr (3)-Ph) (7), [PhBP (3)] CoS (2,4,6-(t)() Bu (3)-Ph) (8), [PhBP (3)] CoSSiPh (3) (9), [PhBP (3)] CoOSi (4-NMe (2)-Ph)(3) (10), [PhBP (3)] CoOSi (4-CF (3)-Ph)(3) (11), [PhBP (3)] CoOCPh (3) (12), [PhBP (i)()(Pr)(3)] CoOSiPh (3) (14), and [PhBP (i)()(Pr)(3)] CoSSiPh (3) (15). The low-temperature solid-state crystal structures of 2, 3, 5-10, 12, and 15 are also described. These pseudotetrahedral cobalt (II) complexes are classified as featuring one of two limiting distortions, either umbrella or off-axis. Magnetic and spectroscopic data demonstrate that both S = (1)/(2) and S = (3)/(2) ground-state electronic configurations are accessible for the umbrella distorted structure type, depending on the nature of the X-type ligand, its denticity (eta (1) versus eta (3)), and the tripodal phosphine ligand employed. Off-axis distorted complexes populate an S = (1)/(2) ground-state exclusively. For those four-coordinate complexes that populate S = (1)/(2) ground states, X-ray data show two Co-P bond distances that are invariably shorter than a third Co-P bond. The pseudotetrahedral siloxides 2, 10, and 11 are exceptional in that they display gradual spin crossover in the solid state. The diamagnetic cobalt (III) complex {[PhBP (3)] CoOSiPh (3)}{BAr (4)} ({16}{BAr (4)}) (Ar = Ph or 3,5-(CF (3))(2)-C (6) H (3)) has also been prepared and structurally characterized. Accompanying electronic structure calculations (DFT) for complexes 2, 6, and {16}(+) support the notion of a close electronic structure relationship between these four-coordinate systems and octahedral, sandwich, and half-sandwich coordination complexes. |
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