The hydrothermal synthesis, single-crystal structure analysis, spectroscopic studies, and thermal stability of the compounds Ca-2(In1-xFex)(PO4)(HPO4)(2). H2O (0 less than or equal to x less than or equal to 1) are reported. The framework of these new phases is based on linear chains (//[101]) formed by (MO6) octahedra and (PO4)/(HPO4) tetrahedra sharing centers. The (HPO4) 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: Ca2In(PO4)(HPO4)(2). H2O, space group C2/c (No. 15), a = 7.573(1) Angstrom, b = 15.838(1) Angstrom, c = 9.3126(7) Angstrom, beta = 113.55(1)degrees; Ca-2(In0.5Fe0.5) (PO4)(HPO4)(2). H2O, C2/c (No. 15), a = 7.548(2) Angstrom, b = 15.670(3) Angstrom, c = 9.241(2) Angstrom, beta = 113.62(3)degrees; Ca2Fe(PO4)(HPO4)(2) H2O, C2/c (No. 15); a = 7.503(2) Angstrom, b = 15.477(2) Angstrom, c = 9.142(1) Angstrom. beta = 113.60(2)degrees. The phases lose two water molecules between 350 and 600 degrees C to form the series Ca-2(In1-xFex)(PO4)(P2O7) (0 less than or equal to x less than or equal to 1), which are isostructural with Ca2V(PO4)(D2O7). Solid state magic angle spinning (MAS) P-31 NMR of Ca2In(PO4)(HPO4)(2). H2O confirms two phosphorous moieties in roughly a 2:1 ratio. A CP-MAS buildup study yielded polarization transfer rates (T-IS(-1)) of 2128 and 1597 s(-1) for the HPO4 (-2.4 ppm) and PO4 (-0.9 ppm) sites, respectively. A H-1-P-31 WISE experiment indicates the presence of motional narrowing and hydrogen exchange between the water molecules and hydroxyl protons.