No abstract

Two luminescent mix-capped trinuclear copper(I) acetylide complexes, [Cu3(μ-dppm)3(μ3-η1-C⋮CC6H4OMe-p)(μ3-η1-C⋮CC6H4OEt-p)]PF6 (1) and [Cu3(μ-dppm)3(μ3-η1-C⋮CC6H4OMe-p)(μ2-η1-C⋮CC6H4NO2-p)]PF6 (2), have been synthesized and their photophysical and electrochemical properties studied. The X-ray crystal structures of 1 and 2 have also been determined.

C(8*) P(1*) P(6*) Cu(1*) P(2*) C(6*) P(3*) Cu(2*) C(1*) C(2*) Cu(3*) P(5*) C(7*) P(4*) C(3*) C(4*) C(5*) C(5) C(4) C(3) P(4) C(2) C(7) C(1) Cu(2) P(3) C(6) P(2) Cu(1) P(5)

SUB i l T 0 100 0200 0300 0400 0500 0600 a-Fig. 1. The variation of C C distances at the TS as a function of x. Filled circles: results of calculations with the ECP basis set; asterisks: results ofcalculations with the 6-31G* basis set (systems a', d', and g'), gray band: area of mechanistic changeover.of the R,, distances, calculated for the transition states of the reactions of systems I, against the index a. It is seen that the C-C distances in the transition states decrease linearly as a increases; in the ET-TS structures, RC,>2.4S1 A, while in the SUB-TS structures. R,, 2 = 2.370 A. These two critical values, 2.370 and 2.481 A, define the mechanistic changeover zone from the C-ET to C-SUB, over a narrow range of approximately 0.1 A. It follows therefore that the ETjSUB dichotomy characterized by Figure 1 corresponds to two mutually exclusive mechanisms that exhibit a continuous mechanistic spectrum with a narrow changeover zone from C-ET to C-SUB. Thus, while TS earliness is gauged by the Marcus parameter of the ET process, the C-ET + C-SUB mechanistic changeover itself originates in the multiconfigurational nature of the problem, which is chardcterized by the VB mixing of at least three VB configurations.["]We have described here the first structural foundations for the long-sought['". b, 31 ETjSUB dichotomy in a set of reactions of radical anions (A*-) and alkyl halides (RX). There seems to be a continuous spectrum of distances between the reactants in the ET-TS, and at a certain minimum distance there is a mechanistic changeover to the SUB-TS. Thus, the ET series up to the changeover zone exhibits an ET-TS with variable C-C bonding ranging from weak bonding in cases c and f, to significant bonding in cases a, d, and i. Of course the choice of the computational method may shift the changeover zone, but nevertheless, the sharpness of the zone indicates that ET-TS structures can indeed be strongly bonded and structurally adjacent to their SUB analogs. The critical zone may of course depend on the nature of the A'-/RX family; each family may exhibit i t s own characteristic changeover zone, and its own point of maximum bonding for the ET-TS.sian 92, Rcvision C3, Gaussian, Inc., Pittsburgh, PA, 1992.[6] The term IRC(interna1) is used as in ref. IS]. The reaction pathways were examined also by means of IRC with mass-weighted (MW) coordinates [a], IRC(MW). It was found that the energy along the IRCfinternal) path is consistently lower than that along the IRC(MW) path in all the cases. Hence the IRC(interna1) path qualifies as the path of steepest descent and was therefore used throughout to designate the mechanisms ofthe reactions. a) At the ROHF level both IRC(interna1) and IRC(MW) gave identical mechanistic conclusions for the combinations a-e, g, and h with both the 6-310* and the ECP basis sets (reaction a was tested with many other basis sets-6-31 + G*, 6-31G**, 6-311G*, and 6-311G**-all of which led to the same conclusion, an ET mechanism). b) In U H F (for a, c, g) and UMP2/6-31G* (for a, g), the IRC(inte...