Wang Di, Shi Chengfang, Baumgarten Martin, Wang Wenping, Liu Jin
Anhui Key Laboratory of Advanced Building Materials, School of Materials Science and Chemical Engineering, Anhui Jianzhu University, Hefei 230601, China.
School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009, China.
J Org Chem. 2024 Sep 6;89(17):12277-12285. doi: 10.1021/acs.joc.4c01206. Epub 2024 Aug 13.
To explore the distinctions in spin coupling between the molecular bridges of alternating and nonalternating π-systems, we synthesized a pair of isoelectronic compounds, namely, and , by utilizing naphthalene and azulene (naphthalene = Na and azulene = Az) as the bridges, respectively. Moreover, we conducted assessments to predict the coupling paths for nonalternating azulene. Variable-temperature EPR (VT-EPR) and SQUID results consistently reveal that both and exhibit antiferromagnetic coupling interactions, with coupling constants of = -22.3 cm and = -30.1 cm, respectively. Density functional theory computations support these discoveries by revealing negative coupling constants ( < 0) and the spin densities population of the diradicals are observed to delocalize into the molecular bridges. This work suggests the most suitable coupling path for . In addition, we have investigated the potential spatial resistance of the diradicals in conjunction with single-crystal data. Theoretical calculations underestimating the torsion angle of the diradicals and overestimating the value of the magnetic coupling provide an explanation for this phenomenon. The final experimental results and theoretical calculations show that the coupling path prefers short paths.
