SOM assembly of hydroxynaphthoquinone and its oxime: Polymorphic X-ray structures and EPR studies
Résumé
Study on solvent-induced polymorphism in x-ray structures of 2-hydroxy-1,4-naphthoquinone (Lawsone) 1, is carried out. In protic methanol, 1 crystallizes in monoclinic space group P21/c (1a) comprising of 2-dimensional hydrogen bonded network via cyclic dimers. In aprotic solvent such as acetone however, 1 exhibits orthorhombic space group Pna21 (1b) and emerges with 1-dimensional catemeric chain. Solvent-induced topol. isomerism of cyclic dimers and helical catemeric chains arising from (i) bifurcated intra- and inter mol. hydrogen bondings viz. O-H...O-C interactions between C(2) hydroxyl and C(1), C(4) carbonyls, (ii) C-H...O interactions viz., C(3)-H...O(1)C(1) were discussed. A signal for radical in 1 at g = 2.0058 is signatured by EPR spectrum and it's oxime deriv. viz. 2-hydroxy-4-naphthoquinone-1-oxime 2, in solid state shows biradical and monoradical formation with aggregation of dimer and monomer due to noncovalent hydrogen bonds. Zero field split parameters for 2 are D = 215 G, Ex = 13 G, Ey = 47 G at 298 K A half field signal at 77 K indicates triplet ground state. Frozen glass EPR of 2 resolves as regioregular dimeric-monomeric species showing hyperfine interactions with 1-oximino nitrogen in dimer .hivin.A(14N) = 15.5 G. [on SciFinder (R)]