Alkaline earth metal complexes of 1,3-bis(carboxymethyl)benzimidazolium (HL) including [Mg(L) 2 (H 2 O) 4 ]·2H 2 O (1), [Ca(L) 2 (H 2 O) 4 ]·2H 2 O (2) and [Ba(L) 2 (H 2 O) 2 ·2H 2 O] n (3) have been synthesized by a hydrothermal procedure and characterized by X-ray crystallography, spectroscopy and thermoanalysis. The results of X-ray crystallography revealed that complexes 1 and 2 are neutral monomers, while complex 3 is a polymeric species, and the carboxymethyl moiety of the deprotonated ligand (L − ) acts as a bridge between metal ions. The spectroscopic properties of the complexes were evaluated through density functional theory (DFT) and time-dependent density functional theory (TD DFT) calculations. The results revealed that the absorption peaks in UV–Vis spectra were derived from ligand to ligand charge-transfer transitions (LLCT) and/or (p, π)→(σ ∗ , π ∗ ) intraligand charge-transfer (ILCT). HL and HL-based complexes displayed similar emission peaks in the near-UV region due to ligand-based LLCT. The results of the Fukui index of the complexes supported LLCT and ILCT mechanisms. In addition, the calculated value of the luminescence oscillator strength displayed a linear relationship with the charge distribution, and the DFT chemical reactivity index, and correlation coefficients (R 2 ) of 0.999 and 0.996 were obtained, respectively. Thus, the results revealed that the emission strength of the complex can be controlled by coordinating the ligand to different metal ions.