Structural and spectroscopic evidence for weak metal-metal interactions and metal-substrate exciplex formations in d10 metal complexes

Structural investigations of homometallic di- and tri-nuclear coinage metal complexes with bridging phosphine ligands, [M-2((PP)-P-boolean AND)(2)]X-2 and [M-3((PPP)-P-boolean AND-P-boolean AND)(2)]X-3 (M = Cu(I), Au(I), and Ag(I); X = anion), have revealed close intramolecular metal-metal and metal-anion contacts in their crystal lattices, thus providing solid-state evidence for metallophilicity and metal-substrate interactions in two-coordinate d(10) metal ions. To verify the existence of weak closed-shell metal-metal interactions, UV-vis absorption and resonance Raman spectroscopic techniques have been employed. Comparisons of the absorption spectra of [M-2((PP)-P-boolean AND)(2)](2+) and [M-3((PPP)-P-boolean AND-P-boolean AND)(2)](3+) show that the spin- and dipole-allowed [nd sigma* -> (n + 1)p sigma] transition red-shifts in energy from [M-2((PP)-P-boolean AND)(2)](2+) to [M-3((PPP)-P-boolean AND-P-boolean AND)(2)](3+). This spectral assignment was confirmed by resonance Raman spectroscopy, which reveals stronger metal-metal interaction in the (1)[(n + 1)p sigma, nd sigma*] state compared to the ground state. Photoluminescence from the (3)[(n+ 1)p sigma, nd sigma*] excited state was also recorded for the [M-2((PP)-P-boolean AND)(2)]X-2 and [M-3(p(boolean AND)p(boolean AND)P)(2)]X-3 solids, where X is a non-coordinating anion. The spectroscopic data for these metal-centered transitions are supported by theoretical calculations. Perturbations of the M-M bonded excited states through interaction with neighboring solvent molecules or anions lead to exciplex formations with emission in the visible region. The sensitivity of photoluminescence of two-coordinate d(10) metal complexes to metal-ligand coordination provides an entry to new classes of luminescent sensory materials for substrate-binding processes. The (3)[(n + 1)p sigma, nd sigma] excited states of [M-2(p(boolean AND)P)(2)](2+) (M = Cu and Au) systems are powerful reductants and light-induced multi-electron photocatalysis by these systems have been observed. (c) 2005 Elsevier B.V. All rights reserved.