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Britto, Sylvia,Leskes, Michal,Hua, Xiao,Hé,bert, Claire-Alice,Shin, Hyeon Suk,Clarke, Simon,Borkiewicz, Olaf,Chapman, Karena W.,Seshadri, Ram,Cho, Jaephil,Grey, Clare P. American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.26
<P>Vanadium sulfide VS<SUB>4</SUB> in the patronite mineral structure is a linear chain compound comprising vanadium atoms coordinated by disulfide anions [S<SUB>2</SUB>]<SUP>2–</SUP>. <SUP>51</SUP>V NMR shows that the material, despite having V formally in the d<SUP>1</SUP> configuration, is diamagnetic, suggesting potential dimerization through metal–metal bonding associated with a Peierls distortion of the linear chains. This is supported by density functional calculations, and is also consistent with the observed alternation in V–V distances of 2.8 and 3.2 Å along the chains. Partial lithiation results in reduction of the disulfide ions to sulfide S<SUP>2–</SUP>, via an internal redox process whereby an electron from V<SUP>4+</SUP> is transferred to [S<SUB>2</SUB>]<SUP>2–</SUP> resulting in oxidation of V<SUP>4+</SUP> to V<SUP>5+</SUP> and reduction of the [S<SUB>2</SUB>]<SUP>2–</SUP> to S<SUP>2–</SUP> to form Li<SUB>3</SUB>VS<SUB>4</SUB> containing tetrahedral [VS<SUB>4</SUB>]<SUP>3–</SUP> anions. On further lithiation this is followed by reduction of the V<SUP>5+</SUP> in Li<SUB>3</SUB>VS<SUB>4</SUB> to form Li<SUB>3+x</SUB>VS<SUB>4</SUB> (<I>x</I> = 0.5–1), a mixed valent V<SUP>4+</SUP>/V<SUP>5+</SUP> compound. Eventually reduction to Li<SUB>2</SUB>S plus elemental V occurs. Despite the complex redox processes involving both the cation and the anion occurring in this material, the system is found to be partially reversible between 0 and 3 V. The unusual redox processes in this system are elucidated using a suite of short-range characterization tools including <SUP>51</SUP>V nuclear magnetic resonance spectroscopy (NMR), S K-edge X-ray absorption near edge spectroscopy (XANES), and pair distribution function (PDF) analysis of X-ray data.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-26/jacs.5b03395/production/images/medium/ja-2015-03395v_0013.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b03395'>ACS Electronic Supporting Info</A></P>