Single crystal electron paramagnetic resonance (EPR), powder X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) and UV–Visible (UV–Vis) spectroscopy studies of Cu(II) doped in hexaaquazinc(diaquabismalonto)zincate (HZDMZ) have been investigated at room temperature. Angular variation of copper hyperfine lines in the three orthogonal planes shows the presence of a single site in substitutional position, with spin Hamiltonian parameters calculated from EPR spectra are g<inf>xx</inf> = 2.3940; g<inf>yy</inf> = 2.0919; g<inf>-zz</inf> = 2.0700; A–<inf>xx</inf> = 13.85 mT; A<inf>yy</inf> = 1.79 mT; A<inf>zz</inf> = 1.39 mT. Molecular orbital coefficients β2 = 0.765 and ε2 = 0.275 have been calculated, which reveal a moderately covalent metal–ligand bond. Optical and EPR data have been collaborated to obtain crystal field parameters, admixture and molecular orbital coefficients. Powder XRD, FT-IR and UV–Vis data confirms the structure of host complex and presence of the dopant. Graphic Abstract: [Figure not available: see fulltext.] © 2021 Elsevier B.V., All rights reserved.