Unravelling the impact of octahedral distortion and non-covalent interactions on the hyperpolarizabilities of Co(II) and Ni(II) coordination complexes with uridine nucleotide

Designing and synthesizing high-performance nonlinear optical (NLO) crystals is a significant and complex challenge in advancing sophisticated laser technology. This study presents two unique one-dimensional coordination complexes, namely, {[Co(UMP)(bipy)(H₂O)₃]·2H₂O}_n (Complex I) and {[Ni(UMP)(bipy)(H₂O)₃]·H₂O}_n (Complex II) (UMP = Uridine Monophosphate, bipy = 4, 4′-bipyridine), was synthesized effectively by the solvent evaporation technique. Complexes (I) and (II) crystallized in non-centrosymmetric monoclinic and orthorhombic P2₁ and P2₁2₁2₁ space groups, respectively. The stabilization of the complexes crystal packing and intermolecular interactions are investigated by crystallography and Hirshfeld surface analysis (HSA). Complex (II) has superior second harmonic generation (β^SHG) relative to Complex (I) and Potassium dihydrogen phosphate (KDP). The NLO properties including static and dynamic polarizability, electro-optic Pockels effect (β^EOPE), second-harmonic generation (β^SHG), Hyper-Rayleigh Scattering (β_HRS), depolarization ratio (DR), electric field-induced second harmonic generation (γ^ESHG) and nonlinear refractive index (n₂) of both complexes were computed and compared using KDP at six different frequencies. Experimental and theoretical analyses have proven that the enhanced hyperpolarizabilities of Complex (II) are strongly associated with a reduced bandgap (E_g), robust non-covalent interactions and increased octahedral distortion in comparison to Complex (I). This study offers novel structural insights for designing and optimizing NLO capabilities in coordination complexes.