The first amine-templated layered metal selenates

Although a few open-framework metal sulfates and selenites have been synthesized and characterized recently, it has not been possible to prepare the corresponding selenates, probably because of the instability of the +6 oxidation state of Se in alkaline media. We have been able to synthesize, for the first time, organically templated open-framework rare earth selenates with the general formula 0.5[C2N2H10][Ln(H2O)(2)(SeO4)(2)] (I) (Ln = La, Nd or Pr) and 0.5[C4N2H14][La(SeO4)(2)].0.5H(2)O (II), under hydrothermal conditions in an acidic medium. Crystal data: I (Ln = La): triclinic, space group = P (1) over bar, Mr = 491.91, a = 7.0105(8) Angstrom, b = 7.3772(9) Angstrom, c = 9.526(1) Angstrom, alpha = 82.014(2), beta = 84.514(2), gamma = 84.247(2)degrees, V = 483.76(1) Angstrom(3), Z = 2; H: triclinic, space group P (1) over bar, Mr = 478.91, a = 5.94(2), b = 7.408(3), c = 11.048(2) Angstrom, alpha = 86.899(2), beta = 75.971 (1), gamma = 79.456(2)degrees, V = 463.7 (2) Angstrom(3), Z = 4. Being the first report of complex layered selenates, it is likely to stimulate efforts to synthesize other novel open-framework structures making use of the selenate ion as the building unit. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).