Crystallographic Insights into the Synthesis and Magnetic Properties of Oxoverdazyl Radicals Functionalized by Benzoic Acid. Issue 3 (22nd November 2017)

• Record Type: Journal Article
• Authors: Kumar, Varun; Shova, Sergiu; Maurel, Vincent; Novitchi, Ghenadie; Train, Cyrille
• Other Names: Le Guennic Boris guestEditor.; Chastanet Guillaume guestEditor.; Pillet Sébastien guestEditor.; Clérac Rodolphe guestEditor.
• Is Part Of: European journal of inorganic chemistry. Issue 3/4(2018)
• Page Start: 517
• Page End: 524
• Publication Date: 2017-11-22
• Subjects: Radicals -- Structure elucidation -- Borohydride -- Boron -- Magnetic properties; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201700950
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : The synthesis and crystallization of two verdazyl radicals, 1, 5‐dimethyl‐3‐(4′‐carboxyphenyl)‐6‐oxoverdazyl HI Me and 1, 5‐diisopropyl‐3‐(4′‐carboxyphenyl)‐6‐oxoverdazyl HI i Pr, are described. The electrochemical studies reveal that the oxidation of the two radicals is reversible, whereas their reduction is irreversible. The EPR spectrum of both radicals essentially exhibits a nine‐line pattern related to the mean hyperfine interaction of the unpaired electron with the nitrogen atoms of the verdazyl cycle. The single‐crystal X‐ray diffraction of the intermediates towards HI i Pr allows a fine description of the cyanoborane adduct, which is the key intermediate of this synthesis. The verdazyl radicals themselves are obtained as single crystals. In the case of HI i Pr, depending on the solvent, two polymorphs are crystallized. The structure resolution reveals that, in the solid state, the organization of the verdazyl radicals is governed by both H‐bonding and π–π interactions and is reminiscent of the H‐bonded structures that can be present in solution. Within the 1D π stacks observed in the three compounds, the verdazyl–verdazyl distance varies from 4.88 Å in HI Me to 7.90 Å in H a I i Pr . This modulation of the distance strongly influences the antiferromagnetic intermolecular exchange interaction between π‐stacked radicals, which goes from J = –90 cm –1 ( H = – J ΣS i S i +1 ) for HI Me to –12.96(3) cm –1 for H b I i Pr and –0.92 cm –1 for H a I i Pr . Abstract : Two new stable verdazyl radicals were synthesized. In the solid state, they are organized as one‐dimensional π stacks. The overlap between the SOMO leads to an antiferromagnetic exchange interaction governed by the verdazyl–verdazyl distance.