The hydrothermal synthesis, single-crystal structure analysis, spectroscopic studies, and thermal stability of the compounds Ca(2)(In(1)(-)(x)()Fe(x)())(PO(4))(HPO(4))(2).H(2)O (0 = x = 1) are reported. The framework of these new phases is based on linear chains (//[101]) formed by (MO(6)) octahedra and (PO(4))/(HPO(4)) tetrahedra sharing corners. The (HPO(4)) groups and water molecules link the chains through hydrogen bonding to form layers stacked perpendicular to the c axis. The calcium cations are located between the layers and are coordinated by nine oxide anions. Crystal data Ca(2)In(PO(4))(HPO(4))(2).H(2)O, space group C2/c (No. 15), a = 7.573(1) Å, b = 15.838(1) Å, c = 9.3126(7) Å, beta = 113.55(1) degrees; Ca(2)(In(0.5)Fe(0.5))(PO(4))(HPO(4))(2).H(2)O, C2/c (No. 15), a = 7.548(2) Å, b = 15.670(3) Å, c = 9.241(2) Å, beta = 113.62(3) degrees; Ca(2)Fe(PO(4))(HPO(4))(2).H(2)O, C2/c (No. 15), a = 7.503(2) Å, b = 15.477(2) Å, c = 9.142(1) Å, beta = 113.60(2) degrees. The phases lose two water molecules between 350 and 600 degrees C to form the series Ca(2)(In(1)(-)(x)()Fe(x)())(PO(4))(P(2)O(7)) (0 = x = 1), which are isostructural with Ca(2)V(PO(4))(P(2)O(7)). Solid state magic angle spinning (MAS) (31)P NMR of Ca(2)In(PO(4))(HPO(4))(2).H(2)O confirms two phosphorous moieties in roughly a 21 ratio. A CP-MAS buildup study yielded polarization transfer rates (T(IS)(-)(1)) of 2128 and 1597 s(-)(1) for the HPO(4) (-2.4 ppm) and PO(4) (-0.9 ppm) sites, respectively. A (1)H-(31)P WISE experiment indicates the presence of motional narrowing and hydrogen exchange between the water molecules and hydroxyl protons.