Layered tin (II) oxalates possessing large apertures

Abstract

Two layered tin(II) oxalate structures have been prepared by hydrothermal methods in the presence of structure-directing organic amines. The crystal data for these structures are as follows: oxalate I, [(CH₃)₂NH(CH₂)₂NH(CH₃)₂ ]²⁺[Sn₂(C₂O₄)₃]^{2 -}·H₂O, monoclinic, space group C2/c (no. 15), a = 16.567 (8) Å, b = 10.851 (6) Å, c = 11.652 (6) Å, β = 102.62 (3)°, V = 2039.0 (1) ų, Z = 4, M = 637.4(1), D_calc = 2.825 g cm^-3, Mo Kα, R_F = 0.04; oxalate II, [C(NH₂)₃]⁺₂ [Sn₄(C₂O₄)₅]^2-·2H₂O, orthorhombic, space group Pbca (no. 61), a = 11.390 (1) Å, b = 14.742 (1) Å, c = 16.755 (1) Å, V = 2813a .1 (1) ų, Z = 8, M = 1070.8(1), D_calc = 2.844 g cm^-3, Mo Kα, R_F = 0.06. In I, pseudo-pentagonal-bipyramidal SnO₆ units form a puckered layered structure by sharing oxygens with the oxalate anions. The layers contain 8- and 12-membered apertures, and the amine (protonated N,N,N'N'--tetramethyl-1,2-diaminoethane) and water molecules are in the interlamellar region where they interact with the framework and with each other by hydrogen bonding. The lone pairs of the Sn(II) atoms point into the interlamellar region. Oxalate II contains both square-pyramidal SnO₄ units and SnO₆ units similar to those in I. These units together form a saw-tooth lamellar structure by linking through the oxalates. The sheets contain 20-membered corrugated rings, which hold two amine cations (guanidinium) and two water molecules, which interact with the framework via hydrogen bonding.