Formation of an asymmetrical ligand (H₃L_cyclic) via a metal-induced cyclization of symmetrical thiocarbohydrazone (H₄L) in synthesizing an oxovanadium(IV) complex VO(HL_cyclic)(EtOH)₂

Abstract

A symmetrical tetraprotic pentadentate (ONS) ligand, 1,5-bis(2-hydroxybenzaldehyde)thiocarbohydrazone (H ₄ L), undergoes metal-induced cyclization to form an asymmetrical triprotic tetradentate ligand (H ₃ L _cyclic) containing a thiadiazole ring when it reacts with [VO(acac)₂] under an aerobic environment in ethanol. The final isolated product is an oxovanadium(IV) complex, VO(HL _cyclic)(EtOH)₂ (1), which contains derived from H ₄ L. Complex 1 has been characterized by X-ray single-crystal structure analysis, ¹H NMR, and EPR. EPR spectrum demonstrates that the oxidation state of vanadium is +4. In 1, O–H ··· N/O–H ··· S hydrogen bond between the free phenolic hydroxyl and N/S of the thiadiazole ring are both possible, probed by density functional theory computation, showing that the hydrogen-bond energy of O–H ··· N is lower than that of O–H ··· S by 8.3 kcal mol⁻¹ and is preferred.

Keywords:

• Thiocarbohydrazone
• Vanadium complex
• Crystal structure
• Cyclization

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant No. 20971091), the Beijing Municipal Natural Science Foundation (Grant No. 2102011), and the Scientific Research Common Program of Beijing Municipal Commission of Education (Grant No. KM201010028008).