Electronic Transitions in Different Redox States of Trinuclear 5, 6, 11, 12, 17, 18‐Hexaazatrinaphthylene‐Bridged Titanium Complexes: Spectroelectrochemistry and Quantum Chemistry. Issue 22 (16th October 2020)

• Record Type: Journal Article
• Authors: Markovic, Aleksandra; Gerhards, Luca; Sander, Pia; Dosche, Carsten; Klüner, Thorsten; Beckhaus, Rüdiger; Wittstock, Gunther
• Is Part Of: Chemphyschem. Volume 21:Issue 22(2020)
• Page Start: 2506
• Page End: 2514
• Publication Date: 2020-10-16
• Subjects: HATN ligand -- intervalence charge transfer -- quantum chemistry -- spectroelectrochemistry -- trinuclear Ti complexes; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.202000547
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: Multinuclear transition metal complexes bridged by ligands with extended π‐electronic systems show a variety of complex electronic transitions and electron transfer reactions. While a systematic understanding of the photochemistry and electrochemistry has been attained for binuclear complexes, much less is known about trinuclear complexes such as hexaphenyl‐5, 6, 11, 12, 17, 18‐hexaazatrinaphthylene‐tristitanocene [(Cp2 Ti)3 HATN(Ph)6 ]. The voltammogram of [(Cp2 Ti)3 HATN(Ph)6 ] shows six oxidation and three reduction waves. Solution spectra of [(Cp2 Ti)3 HATN(Ph)6 ] and of the electrochemically formed oxidation products show electronic transitions in the UV, visible and the NIR ranges. Density functional theory (DFT) and linear response time‐dependent DFT show that the three formally titanium(II) centers transfer an electron to the HATN ligand in the ground state. The optically excited transitions occur exclusively between ligand‐centered orbitals. The charged titanium centers only provide an electrostatic frame to the extended π‐electronic system. Complete active self‐consistent field (CASSCF) calculation on a structurally simplified model compound, which considers the multi‐reference character imposed by the three titanium centers, can provide an interpretation of the experimentally observed temperature‐dependent magnetic behavior of the different redox states of the title compound in full consistency with the interpretation of the electronic spectra. Abstract : More complex? ! The ground state of the three‐nuclear [(Cp2 Ti)3 HATN(Ph)6 ] complex is formed by spin states of different multiplicity and explains the rich electronic transition in the UV‐vis‐NIR ranges in different charge states. Contrary to common notion, IVCT transitions do not play a role in the NIR spectra.