Identification of [M{sup II}(arene){sub 2}]{sup 2+} (M = V, Cr) as the key intermediate in the formation of V[TCNE]{sub x}{sm{underscore}bullet}ysolvent magnets and Cr[TCNE]{sub x}{sm{underscore}bullet}solvent
To elucidate the mechanism of the reaction between V{sup 0}(C{sub 6}H{sub 6}){sub 2} and tetracyanoethylene (TCNE) that leads to the room-temperature magnet V[TCNE]{sub x}{sm{underscore}bullet}yCh{sub 2}Cl{sub 2} (x{approximately}2;y{approximately}1/2), reactions between bis(arene)-vanadium(arene = 1,3,5-trimethylbenzene, 1,3,5-tri-tert-butylbenzene) and its cations and TCNE and its anion were studied. The reaction of V{sup 0}(arene){sub 2} with TCNE yields magnets with critical temperatures ranging from 28 to 400 K. Products from the reaction of [V{sup I}(arene){sub 2}]{sup +} with [TCNE]{sup {sm{underscore}bullet}{minus}} were not magnets; however, reaction of [V{sup I}(arene){sub 2}]{sup +} with [TCNE]{sup {sm{underscore}bullet}{minus}} in the presence of TCNE forms a magnetically ordered material. The reaction of V{sup 0}(1,3,5-C{sub 6}H{sub 3}Me{sub 3}){sub 2} with 2 equiv of one-electron oxidant [Fe{sup III}(5CH{sub 5}){sub 2}]{sup +}, and subsequently with [TCNE]{sup {sm{underscore}bullet}{minus}}, also leads to a magnetic material. The results of these investigations suggest that V{sup 0}(arene){sub 2} undergoes two one-electron oxidation reactions with TCNE to form sequentially [V{sup I}(arene){sub 2}]{sup +} and ``[V{sup II}(arene){sub 2}]{sup 2+}'', the latter being the key intermediate that reacts with [TCNE]{sup {sm{underscore}bullet}{minus}} to produce the magnetic product. [V{sup I}(arene){sub 2}]{sup +} has been isolated, whereas and 11[V{sup II}(arene){sub 2}]{sup 2+}'' has not. The one-electron oxidation of V{sup 0}[C{sub 6}H{sub 3}(t-Bu){sub 3}]{sub 2} with Ag-[BPh{sub 4}] produces {l{underscore}brace}V{sup I}[C{sub 6}H{sub 3}(t-Bu){sub 3}]{sub 2}{r{underscore}brace}{sup +}[BPh{sub 4}]{sup {minus}}. The stoichiometric reaction of V{sup 0}[C{sub 6}H{sub 3}(T-Bu){sub 3}]{sub 2} with TCNE leads to paramagnetic {l{underscore}brace}V{sup I}[1,3,5-C{sub 6}H{sub 3}(tBu){sub 3}]{sub 2}{r{underscore}brace}{sup +}[TCNE]{sup {sm{underscore}bullet}{minus}}. {l{underscore}brace}V{sup I}[C{sub 6}H{sub 3}(t-Bu){sub 3}]{sub 2}{r{underscore}brace}{sup +}[BPh{sub 4}]{sup {minus}} and {l{underscore}brace}V{sup I}[1,3,5-C{sub 6}H{sub 3}(tBu){sub 3}]{sub 2}{r{underscore}brace}{sup +}[TCNE]{sup {sm{underscore}bullet}{minus}} have been structurally characterized. When [V{sup II}(NCMe){sub 6}]{l{underscore}brace}B[3,5-C{sub 6}H{sub 3}(CF{sub 3}){sub 2}]{sub 4}{r{underscore}brace}{sub 2} is reacted with [TCNE]{sup {sm{underscore}bullet}{minus}}, a route that does not use bis(arene)vanadium complexes, a magnetic precipitate is also produced. As established earlier, the reaction of Cr{sup 0}(arene){sub 2} with TCNE forms nonmagnetically ordered [Cr{sup I}(arene){sub 2}]{sup {sm{underscore}bullet}+}-[TCNE]{sup {sm{underscore}bullet}{minus}}. Reaction of lower oxidation potential Cr{sup 0}Np{sub 2} (Np - naphthalene) with TCNE putatively forms ``[Cr{sup II}Np{sub 2}]{sup 2+}'' which reacts with [TCNE]{sup {sm{underscore}bullet}{minus}} to form Cr[TCNE]{sub x}{sm{underscore}bullet}yS, which was isolated and, unexpectedly, does not magnetically order. Similar results are obtained when [Cr{sup II}(NCMe){sub 4}][BF{sub 4}]{sub 2} or [Cr{sup II}(NCMe){sub 6}][B(3,5-C{sub 6}H{sub 3}(CF{sub 3}){sub 2}){sub 4}]{sub 2} is reacted with [{eta}-Bu{sub 4}N][TCNE].
- Research Organization:
- Univ. of Utah, Salt Lake City, UT (US)
- Sponsoring Organization:
- National Science Foundation (NSF); USDOE
- DOE Contract Number:
- FG03-93ER45504; FG02-96ER12198
- OSTI ID:
- 20017329
- Journal Information:
- Journal of the American Chemical Society, Vol. 122, Issue 2; Other Information: PBD: 19 Jan 2000; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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