Rigid molecular rods with cumulene-bridged polyphosphines: synthesis, electronic communication, molecular photophysics, mixed-valence state, and X-ray photoelectron spectroscopic study

Jeffrey V. Ortega, Bo Hong, Sutapa Ghosal, John C. Hemminger, Brian Breedlove, Clifford P. Kubiak

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

The synthesis, molecular photophysics, redox characteristics, and electronic interactions, as well as an X-ray photoelectron spectroscopic (XPS) study of a series of Ru(II) and Os(II) complexes with a polyphosphine/cumulene spacer, namely, 1,1′,4,4′-tetrakis(diphenylphosphino)cumulene (C4P4), are studied and compared with the corresponding systems containing spacers with shorter sp carbon chain (Cn lengths. Characterizations of all mono-, homo-, and heterobimetallic complexes with PF6- counteranions are accomplished using 1H, 13C, and 31P{1H} NMR, fast atom bombardment (FAB/MS), and matrix-assisted laser desorption ionization time-of-fiight (MALDI-TOF/MS) mass spectroscopy and elemental analysis. From the electrochemical study it is observed that the length of the Cn bridges has a profound influence on redox potentials and the electronic interaction between the two metal-based termini. XPS studies reveal that a simple change in carbon chain length affects the electron donation of the phosphine spacer to the metal-based termini. As a result, the redox potential of the Ru(II) or Os(II) center is shifted significantly. The comproportionation constant, Kc, is calculated as 1.3 × 107 (M = RuII) or 4.5 × 1010 (M = OsII) for homobimetallic [(bpy)2M(C4P4)M(bpy)2]4+, suggesting a strong electronic communication across the C4P4 spacer. However, the Kc value is estimated to be ca. 4 for the corresponding complexes [(bpy)2M-(C3P4)M(bpy)2]4+ (M = Ru, Os; C3P4 = 1,1′,3,3′-tetrakis(diphenylphosphino)allene), indicative of a system with electronic isolation between the two termini. In heterobimetallic [(bpy)2Ru(CnP4)Os(bpy)2] 4+ (n = 3, 4), the energy transfer from Ru(II) to Os(II) is found to be very efficient, with rate constants kcn of ca. 3 × 109 s-1 (n = 3) and 1 × 1011 s-1 (n = 4). The increased value of ken upon the change from C3 to C4 can be explained by the increase in the electronic communication across spacers. Detailed studies and calculations have revealed a Dexter-type of mechanism for the triplet energy transfer in the system.

Original languageEnglish
Pages (from-to)5102-5112
Number of pages11
JournalInorganic chemistry
Volume38
Issue number22
Publication statusPublished - 1999 Dec 1
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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