PAPER www.rsc.org/dalton | Dalton Transactions Structural, spectroscopic, and electrochemical behavior of trans-phenolato cobalt(III) complexes of asymmetric NN ′ O ligands as archetypes for metallomesogens Rajendra Shakya, a Camille Imbert, a Hrant P. Hratchian, a Mauricio Lanznaster, a Mary Jane Heeg, a Bruce R. McGarvey, b Marco Allard, a H. Bernhard Schlegel a and Claudio N. Verani* a Received 6th October 2005, Accepted 10th February 2006 First published as an Advance Article on the web 3rd March 2006 DOI: 10.1039/b514190g In order to understand and predict structural, redox, magnetic, and optical properties of more complex and potentially mesogenic electroactive compounds such as [Co III (L t-BuLC ) 2 ]ClO 4 (1), five archetypical complexes of general formula [Co III (L RA ) 2 ]ClO 4 , where R = H(2), tert-butyl (3), methoxy (4), nitro (5), and chloro (6), were obtained and studied by means of several spectrometric, spectroscopic, and electrochemical methods. The complexes 2, 4, and 6 were characterized by single-crystal X-ray diffraction, and show the metal center in an approximate D 2h symmetry. Experimental results support the fact that the electron donating or withdrawing nature of the phenolate-appended substituents changes dramatically the redox and spectroscopic properties of these compounds. The 3d 6 electronic configuration of the metal ion dominates the overall geometry adopted by these compounds with the phenolate rings occupying trans positions to one another. Formation of phenoxyl radicals has been observed for 1, 3, and 6, but irreversible ligand oxidation takes place upon bulk electrolysis. These data were compared to detailed B3LYP/6-31G (d)-level computational calculations and have been used to account for the results observed. A comparison between compound 1 and archetype 3, validates the approach of using archetypical models to study metal-containing soft materials. Introduction Interest in metal-containing soft materials has increased due to applications towards molecular electronics 1 and magnetic films. 2 These materials are usually composed of an organic fragment attached to a ligand capable of coordinating metals. Rigid ligands such as terpy (2,6-di(pyridin-2-yl)pyridine) and R 2 bzimpy (2,6-bis[N ′ -R-benzimidazol-2-yl]pyridine, R = H, Me) have been used to append different groups, thus forming building blocks for molecular transistors, 3 polymers, 4 liquid crystals, 5 and plastics. 6 More flexible alkylpyridyl ligands have been used for sensing purposes, 7–9 whereas asymmetric tridentate ligands remain largely unexplored. The design of soft materials based on these ligands leads to unique physical properties associated with dissimilar donor sets and metallation is expected to allow for some control over the final behavior of these materials. 10 Our group is interested in soft materials with electroactive and metallomesogenic properties as alternatives to phase-dependent spin-crossover switching. 1 The ground state switching mechanism in such metallomesogens is supposedly phase-independent, thus broadening the potential for molecular electronic applications. Ongoing research in our laboratories focuses on asymmetric ligands with pyridine and phenol pendant-arms, and we have developed a new ligand HL t-BuLC along with its first cobalt complex [ Co III (L t-BuLC ) 2 ]ClO 4 (1). Compound 1 was thoroughly a Department of Chemistry, Wayne State University, 5101 Cass Ave., Detroit, MI 48202, USA. E-mail: cnverani@chem.wayne.edu b Department of Chemistry and Biochemistry, University of Windsor-401 Sunset Ave., Windsor, ON N9B 1P4, Canada Scheme 1 characterized and exhibited a complex electrochemical behavior, but attempts to obtain crystallographic information failed. In order to model and predict the behavior of this class of metal- containing soft material, we have followed the widely accepted bioinorganic approach of using model complexes to mimic structural and electronic properties of active centers in enzymes. 11 In this bioinspired approach, we investigated a series of discrete archetypical complexes [Co III (L RA ) 2 ]ClO 4 that retain key attributes of 1 (Scheme 1), by means of mass spectrometry, vibrational, electronic, and EPR spectroscopy, and electrochemical methods. The results obtained from these archetypes will allow us to infer important characteristics of 1 leading to a better understanding of its behavior, as well as a more rational approach to the synthesis and expected properties of similar materials. Complexes 2, 4, and 6 This journal is © The Royal Society of Chemistry 2006 Dalton Trans., 2006, 2517–2525 | 2517