Introduction of the citric acid in the borate system generates a new phase, Ca[B(C6H6O7)2](H2O) 4s˙HCl, which is transparent from 195 nm to near infrared region. Single crystals of Ca[B(C6H6O7) 2](H2O)4s˙HCl with dimensions up to 7 × 5 × 2 mm3 were successfully grown by slow evaporation method at room temperature. It has been characterized by single crystal X-ray diffraction, infrared spectroscopy measure and thermogravimetric analysis. Ca[B(C6H6O7)2](H2O) 4s˙HCl crystallizes in the triclinic space group P - 1, with a = 6.3243(18) A˚, b = 8.365(2) A˚, c = 19.042(5) A˚, α = 97.291(3)°, β = 94.535(4)°, γ = 94.165(4)°. It exhibits a unique layered structure, the layers are parallel arrangement of the (0 0 1) plane and stack along the c-axis.
