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Tailoring of the Frontier Orbital Character in Co 2+/3+ Complexes with Triarylamine Substituted Terpyridine Ligands
Author(s) -
Schnaubelt Linda,
Petzold Holm,
Hörner Gerald,
Rüffer Tobias,
Klein Niels,
Lang Heinrich
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201801433
Subject(s) - chemistry , singlet state , open shell , terpyridine , spin states , crystallography , diradical , homo/lumo , solvent , charge (physics) , photochemistry , stereochemistry , atomic physics , molecule , inorganic chemistry , excited state , metal , organic chemistry , physics , quantum mechanics
Tara‐decorated terpyridines 1 – 3 and their 1:2 Co 2+ [Co( L ) 2 ](ClO 4 ) 2 ( L = 1 – 3 ) and Co 3+ complexes [Co( L ) 2 ](ClO 4 ) 2 (SbCl 6 ) ( L = 1 , 3 ) are reported. The solid‐state complex metrics of [Co( 3 ) 2 ] 2+ and [Co( 1 ) 2 ] 3+ indicate an assignment as spin‐quartet Co 2+ or spin‐singlet Co 3+ , which is in accord with DFT and 1 H NMR studies. Vis‐NIR spectra of 1 [Co 3+ ( L ) 2 ] 3+ show characteristic Tara→Co 3+ charge‐transfer bands, giving no direct indication of L ‐based oxidation events, irrespective of the solvent. Theoretical studies reveal no charge transfer induced spin transition in [Co 3+ ( L ) 2 ] 3+ , although a substantial decrease of the HOMO‐LUMO gap prevails in [Co 3+ ( 1 ) 2 ] 3+ as compared with [Co(tpy) 2 ] 3+ . The destabilisation of the HOMO is not sufficient to allow an equilibration among closed‐ and open‐shell formulations. The computed singlet‐triplet and singlet‐quintet splitting in [Co( 1 ) 2 ] 3+ renders these open‐shell formulations to reside only moderately above the ground state. Design criteria are derived from this analysis aiming at a further stabilisation of the open‐shell species through implementation of more strongly electron releasing Tara substituents.