Structural variability of 4f and 5f thiocyanate complexes and dissociation of uranium(III)‒ thiocyanate bonds with increased ionicity

Biswas, Saptarshi, Ma, Shuwen, Nuzzo, Stefano, Twamley, Brendan, Russell, Andrew T., Platts, James A., Hartl, František and Baker, Robert J. 2017. Structural variability of 4f and 5f thiocyanate complexes and dissociation of uranium(III)‒ thiocyanate bonds with increased ionicity. Inorganic Chemistry 56 (23) , pp. 14426-14437. 10.1021/acs.inorgchem.7b01560

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Abstract

A series of complexes [Et4N][Ln(NCS)4(H2O)4] (Ln = Pr, Tb, Dy, Ho, Yb) have been structurally characterized, all showing the same structure, namely a distorted square antiprismatic coordination geometry, and the Ln–O and Ln–N bond lengths following the expected lanthanide contraction. When the counterion is Cs+, a different structural motif is observed and the eight-coordinate complex Cs5[Nd(NCS)8] isolated. The thorium compounds [Me4N]4[Th(NCS)7(NO3)] and [Me4N]4[Th(NCS)6(NO3)2] have been characterized, and high coordination numbers are also observed. Finally, attempts to synthesize a U(III) thiocyanate compound has been unsuccessful; from the reaction mixture, a heterocycle formed by condensation of five MeCN solvent molecules, possibly promoted by U(III), was isolated and structurally characterized. To rationalize the inability to isolate U(III) thiocyanate compounds, thin-layer cyclic voltammetry and IR spectroelectrochemistry have been utilized to explore the cathodic behavior of [Et4N]4[U(NCS)8] and [Et4N][U(NCS)5(bipy)2] along with a related uranyl compound [Et4N]3[UO2(NCS)5]. In all examples, the reduction triggers a rapid dissociation of [NCS]− ions and decomposition. Interestingly, the oxidation chemistry of [Et4N]3[UO2(NCS)5] in the presence of bipy gives the U(IV) compound [Et4N]4[U(NCS)8], an unusual example of a ligand-based oxidation triggering a metal-based reduction. The experimental results have been augmented by a computational investigation, concluding that the U(III)–NCS bond is more ionic than the U(IV)–NCS bond.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Advanced Research Computing @ Cardiff (ARCCA) Chemistry
Publisher:	American Chemical Society
ISSN:	0020-1669
Date of First Compliant Deposit:	17 November 2017
Date of Acceptance:	13 November 2017
Last Modified:	28 Jun 2019 18:59
URI:	http://orca.cf.ac.uk/id/eprint/106689

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