S. Zamisa, Unathi Bongoza, B. Omondi
Aug 14, 2021
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Acta Crystallographica Section A Foundations and Advances
Abstract
N,N’-diphenyl formamidines have E and Z isomers with either synperiplanar or antiperiplanar conformational combinations around the formamidine –N=C(H)–N(H)– backbone. The molecular isomerism of N,N’-diphenyl formamidines have been extensively studied in solution state [1]. However, no reports have been found regarding their preferred isomerism in the solid state. In this work, the steric and electronic effects on the molecular isomerism of eight N,N’-diphenyl formamidine derivatives in solid-state were evaluated using X-ray crystallography [2]. The eight compounds constitute of four symmetrical and four unsymmetrical N,N'-diphenyl formamidine derivatives having a general formula of [N-(Ar),N′-(Ar′)] where (Ar = Ar′) and (Ar ≠ Ar′), respectively. Five of the compounds were characterized using single crystal X-ray diffraction. Solid-state structure analysis showed two molecular isomers, Esyn and Eanti, and they form distinct classical hydrogen bonding patterns (Fig. 1). Correlations between molecular isomerism, pairwise interaction energies, infrared spectroscopy and thermal properties were established in this work. This provides a unique crystal engineering approach to predicting the isomerism of N,N’-diphenyl formamidines without crystal structure determination.