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Published September 12, 2016 | Supplemental Material
Journal Article Open

Rhenium(I) Tricarbonyl Complexes with Peripheral N-Coordination Sites: A Foundation for Heterotrimetallic Nonlinear Optical Chromophores

Abstract

The compounds 4,4′-dicyano-2,2′-bipyridyl (dcbpy), 4,4′-bis(4-cyanophenyl)-2,2′-bipyridyl (bcpbpy), 4,4′-bis[(E)-2-(4-cyanophenyl)vinyl]-2,2′-bipyridyl (bcpvbpy), and 4,4′-bis[(E)-2-(4-pyridyl)vinyl]-2,2′-bipyridyl (bpvbpy) are used to prepare nine new complexes with fac-{Re^I(CO)_3(L)}^(n+) (L = Cl^–, MeCN, pyridine (py), or 4-cyanopyridine (cpy)) centers. The cationic complexes are isolated as their OTf^– salts. These new monometallic species are studied together with the known fac-Re^ICl(CO)_3(qpy) (qpy = 4,4′:2′,2″:4″,4‴-quaterpyridyl) (de Wolf, P.; et al. Inorg. Chim. Acta 2003, 355, 280–285). Coordination of {Ru^(II)(NH_3)_5}^(2+) centers to the peripheral N atoms of fac-Re^ICl(CO)_3(qpy) and fac-[Re^I(CO)_3(bcpbpy)(py)]^+ affords heterotrimetallic complexes that are isolated as their PF_6^– salts. Single-crystal X-ray structures are reported for the solvates fac-Re^ICl(CO)_3(dcbpy)·Me_2CO, fac-[Re^I(CO)_3(dcbpy)(MeCN)]OTf·PhMe, fac-[Re^I(CO)_3(dcbpy)(py)]OTf·0.5PhMe, fac-[ReI(CO)3(dcbpy)(cpy)]OTf·0.5Me2CO, fac-Re^ICl(CO)_3(bcpbpy)·0.5PhMe, and fac-[Re^I(CO)_3(bcpbpy)(MeCN)]OTf·MeCN. Cyclic voltammetry reveals irreversible ReII/I processes in all cases, while the trimetallic compounds show a reversible two-electron RuIII/II oxidation wave. Ligand-based reductions are generally irreversible, but reversible waves are observed for the dcbpy complexes. Electronic absorption spectra show strong d → π^* metal-to-ligand charge-transfer (MLCT) and intraligand π → π^* absorptions. The Ru^(II)-based MLCT bands have lower energies and higher intensities than the ReI-based ones. The monometallic species emit weakly in the red/NIR region (λ_(em) = 594–732 nm; ϕ = 0.6–8.1%) when excited at 350–520 nm. Molecular first hyperpolarizabilities β for the trimetallic complex salts are measured in MeCN solutions via the hyper-Rayleigh scattering technique at 1064 nm. Stark (electroabsorption) spectroscopic studies on the low-energy MLCT bands in frozen PrCN allow the indirect estimation of static first hyperpolarizabilities β_0. The trimetallic complexes have relatively large β_0 values, ca. 500 × 10^(–30) esu or more, which are substantially greater than those of the monometallic species.

Additional Information

© 2016 American Chemical Society. Received: July 1, 2016. Published: August 23, 2016. We thank the EPSRC (a Ph.D. studentship for R.A.P. and grants EP/D070732/1, EP/J018635/1, and EP/K039547/1), the Fund for Scientific Research-Flanders (FWO-V, G.0312.08), and the University of Leuven (GOA/2011/03) for support. B.S.B. acknowledges the Beckman Institute of the California Institute of Technology for support. The authors declare no competing financial interest.

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August 20, 2023
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