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Issue 38, 2012
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Spectroscopic and magnetic properties of an iodo CoI tripodal phosphine complex

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Reaction of the tripodal phosphine ligand 1,1,1-tris((diphenylphosphino)phenyl)ethane (PhP3) with CoI2 spontaneously generates a one-electron reduced complex, [(PhP3)CoI(I)] (1). The crystal structure of 1 reveals a distorted tetrahedral environment, with an apical Co–I bond distance of ∼2.52 Å. CoII/I redox occurs at an unusually high potential (+0.38 V vs. SCE). The electronic absorption spectrum of 1 exhibits an MLCT peak at 320 nm (ε = 8790 M−1 cm−1) and a d–d feature at 850 nm (ε = 840 M−1 cm−1). Two more d–d bands are observed in the NIR region, 8650 (ε = 450) and 7950 cm−1 (ε = 430 M−1 cm−1). Temperature dependent magnetic measurements (SQUID) on 1 (solid state, 20–300 K) give μeff = 2.99(6) μB, consistent with an S = 1 ground state. Magnetic susceptibilities below 20 K are consistent with a zero field splitting (zfs) |D| = 8 cm−1. DFT calculations also support a spin-triplet ground state for 1, as optimized (6-31G*/PW91) geometries (S = 1) closely match the X-ray structure. EPR measurements performed in parallel mode (X-band; 0–15 000 G, 15 K) on polycrystalline 1 or frozen solutions of 1 (THF/toluene) exhibit a feature at g ≈ 4 that arises from a (Δm = 2) transition within the MS = <+1,−1> manifold. Below 10 K, the EPR signal decreases significantly, consistent with a solution zfs parameter (|D| ≈ 8 cm−1) similar to that obtained from SQUID measurements. Our work provides an EPR signature for high-spin CoI in trigonal ligation.

Graphical abstract: Spectroscopic and magnetic properties of an iodo CoI tripodal phosphine complex

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The article was received on 07 Jun 2012, accepted on 31 Jul 2012 and first published on 20 Aug 2012

Article type: Paper
DOI: 10.1039/C2DT31229H
Citation: Dalton Trans., 2012,41, 11788-11797
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    Spectroscopic and magnetic properties of an iodo CoI tripodal phosphine complex

    M. J. Rose, D. E. Bellone, A. J. Di Bilio and H. B. Gray, Dalton Trans., 2012, 41, 11788
    DOI: 10.1039/C2DT31229H

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