Reaction of the diphosphazane-bridged diruthenium derivatives Ru2(M-CO)(CO)4[u-(RO)2PN(Et)P(OR)2]2 (R = Me, 'Pr) with the electron acceptors TCNX (X = Q, E) affords products of the type {Ru2(CO)5[/it-(R0)2PN-(Et)P(OR)2]2(s1-TCNX)}(TCNX) containing a TCNX radical anion in both the inner and outer coordination sphere of the cation. The contribution of the coordinated TCNX*™ to the EPR/ENDOR and UV/vis/near-IR spectra of these salts is partly obscured by that of the external, completely dissociated ¿^/.-symmetric TCNX-, but the infrared vibrational spectra and, in particular, the cyclic voltammograms show clearly the presence of both coordinated and noncoordinated species. Four distinct and reversible waves appear in benzonitrile; two correspond to the TCNX0/™ and TCNX™/* 12™ couples of the external TCNX, while the other pair, shifted by ca. 0.3 V to more positive potentials because of rather weak Ru -* TCNX back-donation, are readily assigned to the corresponding redox couples of the coordinated TCNX. The external TCNQ-anion of the TCNQ salts is readily exchanged for the diamagnetic tetraphenylborate anion to give compounds of the type {Ru2(CO)5^-(RO)2PN(Et)P(OR)2]2(V-TCNQ)}(BPh4) (R = Me, 'Pr), thus enabling UV/vis/near-IR, IR, and EPR spectra of the coordinated TCNQto be recorded in CH2CI2 without interference from the external TCNQanion; the IR and EPR data confirm the low symmetry of the 7;'-bound TCNQ-. With the aid of HMO/McLachlan perturbation calculations and ENDOR measurements it proved possible, for the first time, to record and reproduce EPR spectra of a coordinated TCNQanion; the and 14N hyperfine coupling constants used to simulate the EPR spectra fit the pattern calculated for a TCNQ-bonded in the tj'-mode to one metal center. Replacement of the external TCNEin the TCNE salts by a diamagnetic anion could not be achieved, but since the external TCNEis more easily oxidized than bound TCNE-, selective oxidation of the former in situ to diamagnetic neutral TCNE could be accomplished, thus allowing EPR spectra of the coordinated TCNEto be recorded in CH2CI2 without interference from external TCNE*™. Successful reproductions of the highly resolved EPR spectra showed that, like TCNQ-, TCNEis bonded in the Tj'-mode to one metal center. In situ oxidation of {Ru2(CO)5[At-(RO)2PN(Et)P(OR)2]2(i?1-TCNX)}+ (R = Me, 'Pr) affords the completely oxidized dications containing a neutral coordinated TCNX ligand; these dications, as well as the reduced species {Ru2(C0)5[#i-('Pr0)2PN(Et)P(0'Pr)2]2(77'-TCNQ)}, were characterized by UV/vis/near-IR spectroscopy.

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