A novel crystalline complex of benzoic acid with barium has been successfully grown in sodium metasilicate gel and its structure has been determined by single crystal X-ray diffraction technique. The crystal belongs to triclinic system with space group P-1 having unit cell parameters a = 7.7064(3)Å, b = 12.8642(5)Å, c = 15.4986(7)Å, α = 86.456(2)° β = 87.080(2)° and γ = 89.835(2)°. The complex exhibits a 3D polymeric structure. This polymeric structure is formed by tetradentate chelating and bidentate bridging of carboxylic oxygens of benzoic acid ligand. Another interesting feature of this polymer is the involvement of deprotonated coordinated aqua molecules in bridging the two metal atoms. The TGA/DTA studies reveal that the complex is thermally stable up to 170 °C. The kinetic and thermodynamic parameters at different decomposition stages were also calculated. FT-IR spectral studies were used to identify the functional groups and the bonding sites of the ligand with the metal atoms. UV-Vis spectroscopy revealed the transparency of the crystal. The optical band gap was found to be 4.1 eV. © 2013 Published by Elsevier Masson SAS.