Synthesis, crystal structure, Hirshfeld surface analysis and theoretical investigation of polynuclear coordination polymers of cobalt and manganese complexes with nitrobenzene and pyrazine

•Synthesis of novel compounds by using synthetic approach.•Characterization of novel compounds were done through UV–Vis and Hirshfeld surface (HS) analysis.•Frontier molecular orbital energies and MEPs were calculated.•Exploration of NLO properties were performed. Herein, two new cobalt and manganese-based polymers named as catena‑Poly[[diaquabis(4-nitrobenzoato-κO1)cobalt(II)]-µ-pyrazine-κ2N:Nʹ] (COPNO2) and catena‑Poly[[diaquabis(4-nitrobenzoato-κO1)manganese(II)]-µ-pyrazine–κ2N:Nʹ] (MNPNO2) were synthesized. The crystal structure of COPNO2 and MNPNO2 was determined and explored by X-rays diffraction method. OH⋯O, CH⋯π, NO⋯π, and π⋯π stacking interactions were the key aspects of the crystal packing of COPNO2, whereas for MNPNO2, OH⋯O, CH⋯π, and π⋯π stacking interactions were the key aspects of the crystal packing. The Hirshfeld surface (HS) studies were accomplished for further investigation of the intermolecular interactions. In addition to that, density functional theory (DFT) computations for COPNO2 and MNPNO2 had been carried out at M06 functional, to obtain optimized geometries and double-check the experimental results. Moreover, DFT calculations at the M06 level manifest excellent correlation with the experimental data, which validates the clarity of cobalt and manganese-based polymers. Frontier molecular orbital (FMO) findings were explored to describe nonlinear optical (NLO) properties. The energy gap of COPNO2 was 0.81 eV, while MNPNO2 was examined as 2.16 eV. The global reactivity parameters of COPNO2 and MNPNO2 were determined from the FMO energies. The global reactivity parameters showed that COPNO2 and MNPNO2 have the more donating ability. The NLO results of MNPNO2 (βtot = 1259.17178a.u.) were observed better than COPNO2 (βtot = 34,678.44833a.u.). We propose that this synergistic (experimental-computational) study of COPNO2 and MNPNO2 may deliver new ways for its exploitation as NLO material for hi-tech applications.