Consequences of N,C,N′- and C,N,N′-Coordination Modes on Electronic and Photophysical Properties of Cyclometalated Aryl Ruthenium(II) Complexes

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• 作者：Sipke H. Wadman^† ; ; Martin Lutz^‡ ; ; Duncan M. Tooke^‡ ; ; Anthony L. Spek^‡ ; ; Frantiek Hartl^§ ; ; Remco W. A. Havenith
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：March 2, 2009
• 年：2009
• 卷：48
• 期：5
• 页码：1887-1900
• 全文大小：423K
• 年卷期：v.48,no.5(March 2, 2009)
• ISSN：1520-510X

文摘

The effects of isoelectronic replacement of a neutral nitrogen donor atom by an anionic carbon atom in terpyridine ruthenium(II) complexes on the electronic and photophysical properties of the resulting N,C,N′- and C,N,N′-cyclometalated aryl ruthenium(II) complexes were investigated. To this end, a series of complexes was prepared either with ligands containing exclusively nitrogen donor atoms, that is, [Ru(R¹-tpy)(R²-tpy)]²⁺ (R¹, R² = H, CO₂Et), or bearing either one N,C,N′- or C,N,N′-cyclometalated ligand and one tpy ligand, that is, [Ru(R¹-N^/\C^/\N)(R²-tpy)]⁺ and [Ru(R¹-C^/\N^/\N)(R²-tpy)]⁺, respectively. Single-crystal X-ray structure determinations showed that cyclometalation does not significantly alter the overall geometry of the complexes but does change the bond lengths around the ruthenium(II) center, especially the nitrogen-to-ruthenium bond length trans to the carbanion. Substitution of either of the ligands with electron-withdrawing ester functionalities fine-tuned the electronic properties and resulted in the presence of an IR probe. Using trends obtained from redox potentials, emission energies, IR spectroelectrochemical responses, and the character of the lowest unoccupied molecular orbitals from DFT studies, it is shown that the first reduction process and luminescence are associated with the ester-substituted C,N,N′-cyclometalated ligand in [Ru(EtO₂C−C^/\N^/\N)(tpy)]⁺. Cyclometalation in an N,C,N′-bonding motif changed the energetic order of the ruthenium d_zx, d_yz, and d_xy orbitals. The red-shifted absorption in the N,C,N′-cyclometalated complexes is assigned to MLCT transitions to the tpy ligand. The red shift observed upon introduction of the ester moiety is associated with an increase in intensity of low-energy transitions, rather than a red shift of the main transition. Cyclometalation in the C,N,N′-binding motif also red-shifts the absorption, but the corresponding transition is associated with both ligand types. Luminescence of the cyclometalated complexes is relatively independent of the mode of cyclometalation, obeying the energy gap law within each individual series.