A novel azo-aldehyde and its Ni(II) chelate; synthesis, characterization, crystal structure and computational studies of 2-hydroxy-5-{(E)-[4-(propan-2-yl)phenyl]diazenyl}benzaldehyde

• A novel azo-salicylaldehyde and its Ni(II) chelate were synthesized and characterized by analytical and spectroscopic studies.
• The X-ray structure of the azo-salicylaldehyde was determined.
• The OH⋯O intra-intermolecular hydrogen bondings and π–π interactions stabilize the crystal structure.
• Optimized structures of the three possible tautomers were obtained using B3LYP method.

A novel azo-salicylaldeyde, 2-hydroxy-5-{(E)-[4-(propan-2-yl)phenyl]diazenyl} benzaldehyde and its Ni(II) chelate were obtained and characterized by analytical and spectral techniques. Molecular structure of the azo chromophore containing azo-aldehyde was determined by single crystal X-ray crystallography. X-ray data show that the compound crystallizes in the orthorhombic, Pbca space group with unit cell parameters a = 11.2706(9), b = 8.3993(7), c = 28.667(2) Å, V = 2713.7(4) Å3 and Z = 8. There is a strong phenol-aldehyde (OH⋯O) hydrogen bond forming a S(6) hydrogen bonding motif in the structure. There is also a weaker inter-molecular phenol-aldeyhde (OH⋯O) hydrogen bonding resulting in a dimeric structure and generating a D22(4) hydrogen bonding motif. Hydrogen bonded dimers are linked by π–π interactions within the structure. The azo-aldehyde ligand behaved as bidentate, coordinating through the nitrogen atom of the azomethine group and or oxygen atom of phenolic hydroxyl group. Additionally, optimized structures of the three possible tautomers of the compound were obtained using B3LYP method with 6-311++G(d,p), 6-31G and 3-21G basis sets in the gas phase. B3LYP/6-311++G(d,p) level is found to be the best level for calculation. The electronic spectra of the compounds in the 200–800 nm range were obtained in three organic solvents.

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