CdB10O14(OH)(4)center dot H2O has been synthesized under boric acid flux condition and characterized by singlecrystal X-ray diffraction, infrared spectra, and UV-vis reflectance spectroscopy. It crystallizes in the monoclinic space group P2(1)/n with a = 7.7277(8), b = 18.95(2), c = 9.8616(10) angstrom, beta = 91.454(1)degrees, V = 1443.7(3) angstrom. The structure consists of [B10O16(OH)(4)] layers of 9-membered borate rings enclosing Cd2+ cations. Adjacent borate layers are interconnected via hydrogen bonding to form a 3D network. It possesses an unprecedented decaborate fundamental building block B10O20. The structure details are discussed together with Sr[B6O9(OH)(2)]center dot 3H(2)O, Pb[B8O11(OH)(4)], Pr[B8O11(OH)(5)], and Nd[B9O13(OH)(4)]center dot H2O, which have correlated FBBs. The band structure calculations show its direct energy band gap of similar to 4.68 eV, in consistent with the estimated value (4.77 eV) from UV-vis. In addition, dielectric constants and refractive indexes are also calculated. (c) 2012 Elsevier Ltd. All rights reserved.