Vitamin K3 family members – Part II: Single crystal X-ray structures, temperature-induced packing polymorphism, magneto-structural correlations and probable anti-oncogenic candidature

Temperature-induced packing polymorphism is observed for vitamin K3 (menadione, 3-methyl-1,4-naphthoquinone, 1). Form 1a crystallizes at 300 K and 1b at 277 K both in the same space group P21/c. Form 1b contains one molecule per asymmetric unit, performing anisotropy in g-factor viz. gz = 2.0082, gy = 2.0055 and gx = 2.0025, whereas form 1a contains two molecules in its asymmetric unit. Vitamin K3 family members 2, [2-hydroxy vitamin K3] and 3, [2-hydroxy-1-oximino vitamin K3] also perform intrinsic neutral active naphthosemiquinone valence tautomers even in dark having spin concentrations due to hydrogen bonding and aromatic stacking interactions which are compared to vitamin K3. The significant lateral C–H⋯O and O–H⋯π bifurcated or π–π∗ interactions are discussed for molecular associations and radical formations. X-ray structure of 3 revealed π–π∗ stack dimers as radicals signatured in EPR as triplet with five hyperfine splits [Ā(14N) = 11.9 G]. The centrosymmetric biradicals in 3 show diamagnetism at high temperature but below 10 K it shows paramagnetism with μeff as 0.19 B.M. Vitamin K3 and its family members inhibit biological activities of acid phosphatase (APase), which are proportional to their spin concentrations. This may relate to their probable anti-oncogenic candidature in future.