Identification of a new family of diphosphate compounds, A(2)(I)B(3)(II)(P2O7)(2): Structures of Ag2Co3(P2O7)(2), Ag2Mn3(P2O7)(2), and Na2Cd3(P2O7)(2)

Syntheses and single-crystal X-ray structural results are reported for thre e new mixed diphosphates of the family A(2)(I)B(3)(II)(P2O7)(2); Ag2CO3(P2O 7)(2) (I), Ag2Mn3(P2O7)(2) (II), and Na2Cd3(P2O7)(2) (III). All crystallize in the triclinic system, space group P1 bar: (I) a = 5.351(4), b = 6.375(4 ), c = 16.532(4) Angstrom, alpha = 80.83(6) beta = 81.45(4), gamma = 72.87( 5)degrees, V 528.9(6), Angstrom (3), Z= 2, D-calc = 4.649 mg/m(3), R/Rw = 0 .0428/0.0548 for 3949 obs. reflns; (II) a = 5.432(7), b = 6.619(6), c = 16. 51(3) Angstrom, alpha = 80.78(8) beta = 82.43(9), gamma = 72.82(7)degrees, V = 557.7(13) Angstrom (3), Z = 2, D-calc = 4.338 mg/m(3), R/Rw = 0.0679/0. 1303 for 2100 obs. reflns and (III) a = 5.67(3), b = 7.08(4), c = 7.90(4) A ngstrom, alpha = 77.0(2), beta = 82.5(2), gamma = 67.8(2)degrees, V = 286(3 ) Angstrom (3), Z= 2, D-calc, = 4.249 mg/m(3), R/Rw = 0.0307/0.0342 for 194 5 obs. reflns. (I) and (II) are isostructural but (III) is of a different t ype. All three structures are characterized by layers of P2O7 groups altern ating with layers of mixed metal atoms. Differences are seen in the conglom erate bonding patterns of B atoms and in the irregular geometry of Ag in (I ) and (II) compared to the octahedral bonding seen for Na in (III). The dif ferences in structure may be understood in terms of the ratios of the ionic radii of A and B atoms.