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Spectroscopic and magnetic properties of an iodo Co^I tripodal phosphine complex

Rose, Michael J. and Bellone, Donatela E. and Di Bilio, Angel J. and Gray, Harry B. (2012) Spectroscopic and magnetic properties of an iodo Co^I tripodal phosphine complex. Dalton Transactions, 41 (38). pp. 11788-11797. ISSN 1477-9226. http://resolver.caltech.edu/CaltechAUTHORS:20120827-095929289

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Abstract

Reaction of the tripodal phosphine ligand 1,1,1-tris((diphenylphosphino)phenyl)ethane (PhP3) with CoI_2 spontaneously generates a one-electron reduced complex, [(PhP3)Co^(I)(I)] (1). The crystal structure of 1 reveals a distorted tetrahedral environment, with an apical Co–I bond distance of ~2.52 Å. Co^(II/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 μ_eff = 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 Co^I in trigonal ligation.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1039/c2dt31229hDOIUNSPECIFIED
http://pubs.rsc.org/en/Content/ArticleLanding/2012/DT/c2dt31229hPublisherUNSPECIFIED
Additional Information:© 2012 Royal Society of Chemistry. Received 7th June 2012, Accepted 31st July 2012. First published on the web 20 Aug 2012. We thank Larry Henling and the late Michael Day for X-ray data collection and crystal structure refinement. We gratefully acknowledge Markus Ribbe (UC Irvine) for generous use of a dual mode EPR cavity. Our work was supported by the NSF CCI Solar Fuels program (CHE-0802907) and by CSER (Gordon and Betty Moore Foundation); MJR acknowledges an ACC-F postdoctoral fellowship from the NSF (CHE-1042009). DEB thanks the Rossum family for a SURF award. The Bruker KAPPA APEXII X-ray diffractometer was purchased via an NSF CRIF:MU award to the California Institute of Technology (CHE-0639094).
Group:CCI Solar Fuels
Funders:
Funding AgencyGrant Number
NSF CCI Solar Fuels programCHE-0802907
Gordon and Betty Moore FoundationUNSPECIFIED
NSF ACC-F postdoctoral fellowshipCHE-1042009
Rossum family SURF awardUNSPECIFIED
NSF CRIF:MU awardCHE-0639094
Record Number:CaltechAUTHORS:20120827-095929289
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120827-095929289
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33552
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:27 Aug 2012 20:55
Last Modified:23 Aug 2016 00:13

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