Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 302 (2023) 123114 Available online 8 July 2023 1386-1425/© 2023 Elsevier B.V. All rights reserved. Spectroscopic, theoretical and computational investigations of novel benzo [b]thiophene based ligand and its M(II) complexes: As high portentous antimicrobial and antioxidant agents Nagesh Gunavanthrao Yernale a, * , Basavarajaiah Suliphuldevara Mathada b , Swami Shivprasad a , Sunilkumar Hiremath a , Prashantha Karunakar c , Adavala Venkatesulu d a Department of Chemistry, Guru Nanak First Grade College, Bidar, Karnataka, India b PG Department of Chemistry, Vijaya College, Bengaluru, Karnataka, India c Department of Biotechnology, Dayananda Sagar College of Engineering (Affliated to Visvesvaraya Technological University, Belagavi), Kumaraswamy Layout, Bangalore 560111, Karnataka, India d Department of PG Studies and Research Centre in Physics, Govt. First Grade College, Hosakote, Bangalore Rural, Karnataka, India HIGHLIGHTS G R A P H I C A L ABSTRACT • Synthesis of novel benzo[b]thiophene based ligand and its Cu(II), Co(II), Ni(II) and Zn(II) complexes. • The synthesized compounds act as high portentous antimicrobial and antioxi- dant agents. • The Cu(II), Ni(II) and Zn(I)) complexes showed promising antimicrobial activity (MIC 25 µg mL 1 ). • In vitro antioxidant activity, and in silico docking studies were carried out against Cytochrome c Peroxidase (PDB ID: 2X08). A R T I C L E INFO Dedicated to Professor Bennikallu Hire Mathada Mruthyunjayaswamy, Department of Chemistry, Gulbarga University, Kalaburagi, Karnataka, India, on the occasion of his 70th Birth Anniversary Keywords: Benzo[b]thiophene Antimicrobial Antioxidant DFT ABSTRACT The reaction of 3-chlorobenzo[b]thiophene-2-carbohydrazide with 4-(diethylamino) salicylaldehyde gave the new ligand; 3-chloro-N’-(4-(diethylamino)-2-hydroxybenzylidene)-benzo[b]thiophene-2-carbohydrazide. The Cu (II), Co(II), Ni(II), and Zn(II) complexes have been successfully prepared. The ligand and the complexes were characterized by analytical, FT-IR, 1 H NMR, mass, UV–visible spectroscopy, molar conductivity, and magnetic susceptibility measurements. The FT-IR spectral data showed that the ligand adopted a tridentate fashion when binding with the metal ions via the nitrogen atoms of the imine (C = N), carboxyl (C = O), and phenolic oxygen (O–H) donor atoms. Density Functional Theory (DFT) estimations for the ligand at the DFT/B3LYP level via 6- 31G ++ (d, p) replicate the structure and geometry. Finally, HOMO and LUMO analyses were used for the charge transfer interface of the structure. Furthermore, molecular docking and ADME calculations were also performed to correlate and interpret the experimental results. The antimicrobial activity study illustrated enhancement in the activity of the free ligand upon complex formation, and the Cu(II) complex (MIC 25 µg mL 1 ) may be * Corresponding author. E-mail address: nageshyernale@gnfgc.ac.in (N.G. Yernale). Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.journals.elsevier.com/spectrochimica-acta-part-a- molecular-and-biomolecular-spectroscopy https://doi.org/10.1016/j.saa.2023.123114 Received 11 March 2023; Received in revised form 4 July 2023; Accepted 6 July 2023