1D Cobalt-Cytidine Monophosphate Coordination Polymer Exhibiting Efficient Ultraviolet Second-Harmonic Generation

In pursuit of new ultraviolet (UV) nonlinear optical (NLO) materials, a novel cobalt-based hydrogen-bonded coordination complex, [complex (1)], is synthesized via a slow evaporation method. Complex (1) crystallizes in the noncentrosymmetric (NCS) space group P2₁ and features a distorted octahedral Co(II) coordination environment that extends into a 3D framework. Remarkably, complex (1) exhibits a strong second-harmonic generation (SHG) response, approximately 7.4 times greater than that of KH₂PO₄ (KDP). The pronounced activity arises from robust hydrogen-bonding interactions that suppress antiparallel packing, as well as from the highly distorted, polarizable Co(II) coordination geometry. In addition, complex (1) exhibits an optical bandgap (3.41 eV), indicating UV transparency. These findings make a complex (1) Co(II)-based framework that can be used in UV NLO applications and emphasize it as an effective synthetic approach to the design of polar metal-organic systems with improved optical properties.