Ni-doped titanate CsxTi2-x/2Nix/2O4 and its protonic derivative HxTi2-x/2Nix/2O4 center dot xH(2)O (x = 0.7) were synthesized and charaterized by means of synchrotron X-ray diffraction, Raman scattering, X-ray photoelectron spectroscopy (XPS), and magnetic measurements. CsxTi2-x/2Nix/2O4 crystallizes in an orthorhombic structure (space group Immm), consisting of infinite two-dimensional (2D) host layers of the lepidocrocite (gamma-FeOOH) type. The substitution of Ni atoms for Ti in the 2D octahedral layers results in negative charges that are compensated by intelayer Cs+ ions. Raman scattering and XPS indicate that local structural perturbations are induced upon exchange of interlayer Cs ions with protons H3O+. Magnetic measurements reveal typical paramagnetism induced by Ni substitution; the effective paramagnetic moment mu(eff) = 1.57(1) mu(B) and Curie-Weiss temperature -2.51 (1) K are obtained for HxTi2-x/2Nix/2O4 center dot xH(2)O. Ni- and Mg-codoped titanates CsxTi2-x/2(NiyMg1-y)(x/2)O-4 (x = 0.7, 0 <= y <= 1) were also reported. The crystal structure, interlayer chemistry, and magnetic properties of the titanates depend on the Ni substitution levels, indicating opportunities for tuning of the properties by controlling the nature and level of lattice substitutions.