Influence of the cation size on the formation of alluaudite-type manganesearsenates: synthesis and characterization of Tl2Mn2(As2O7)(2)center dot 2H(2)O, CsMn3(AsO4)(HAsO4)(2)center dot 3H(2)O, and XMn3(AsO4)(HAsO4)(2) (X =Na, K)

Two isotypic manganese-arsenates, XMn3(AsO4)(HAsO4)(2) (X = K(1),Na(2)), wi th a structure related to the mineral alluaudite, have been synthesized and characterized by single crystal X-ray diffraction. Crystal data: (1) KMn3( ASO(4))(HAsO4)(2), monoclinic, C2/c, a = 12.706(3), b = 12.731(3), c = 6.93 7(2), beta = 113.175(5), Z = 4; (2) NaMn3(AsO4)(HAsO4)(2), monoclinic, C2/c , a = 12.299(3), b = 12.735(3), c = 6.893(2), beta = 113.587(4), Z = 4. The use of larger cations under similar synthesis conditions led to the format ion of two layered compounds, CsMn3(AsO4)(HAsO4)(2). 3H(2)O (3) and Tl2Mn3( As2O7)(2). 2H(2)O (4), which were also obtained in the form of single cryst als and characterized by single crystal X-ray diffraction. Crystal data: (3 ) CsMn3(AsO4)(HAsO4)(2). 3H(2)O, monoclinic, P2(1)/c, a = 16.3389(11), b = 6.6912(4), c = 13.2538(9), beta = 98.666(1), Z = 4; (4) Tl2Mn3(As2O7)(2). 2 H(2)O, monoclinic, P2(1)/c, a = 9.576(7), b = 8.478(6), c = 9.735(7), beta = 99.117(13), Z = 2. TGA/MS, IR and magnetic susceptibility measurements on powder samples of 1, 2, and 3 were performed. (C) 2001 Published by Elsevi er Science Ltd.