Tin(II) Oxalates Synthesized in the Presence of Structure-Directing Organic Amines: Members of a Potentially Vast Class of New Open-Framework and Related Materials

Three new tin(II) oxalate materials, of which one has an open-framework layered structure, have been synthesized hydrothermally in the presence of structure-directing organic amines. Crystal data: oxalate 1, [(CH3)2NH(CH2)4NH(CH3)2]2+[Sn2(C2O4)3]2-, monoclinic, space group P21/c (No. 14) a = 8.427(2) Å, b = 14.257(1) Å, c = 8.868(2) Å, β = 100.3(1)°, V = 1048.3(2) Å3, Z = 4, M = 738.6(1), Dcalc = 2.06(1) g cm-3, Mo Kα, RF = 0.05; oxalate II, [Sn2(C2O4)3]2-·2H2O, triclinic, space group P1̄ (No. 2), a = 7.564(1) Å, b = 10.633(1) Å, c = 12.050(1) Å, α = 87.9(1)°, β = 85.2(1)°, γ = 85.9(1)°, V = 962.8(1) Å3, Z = 2, M = 699.6(1), Dcalc = 2.25(1) g cm-3, Mo Kα, RF = 0.06; oxalate III, [C5N2H16]2+[Sn2(C2O4)3]2-, orthorhombic, space group Pmmn (No. 59), a = 8.281(2) Å, b = 17.828(4) Å, c = 4.585(1) Å, V = 678.4(2) Å3, Z = 4, M = 605.4(1), Dcalc = 2.37(1) g cm-3, Mo Kα, RF = 0.03. In I, the Sn atoms are hexacoordinated with oxygen and form porous tin oxalate sheets with the protonated diamine sitting in the middle of the pore, while, in II, four-coordinated Sn atoms form tin oxalate monomer units which are held together by the protonated guanidium cations. In III, we again see the presence of the anionic tin oxalate monomer units hydrogen bonded to the protonated 1,5-diaminopentane cations giving rise to one-dimensional ribbons. These amine-containing oxalate materials constitute a new family of structures where hydrogen bonding interactions, involving the amines, play an important role. The observation of six-coordination for tin in I which forms a pseudo pentagonal bipyramid akin to that in a 14 electron system in noteworthy. The novel features of oxalate I−III suggest that exploration of various metal dicarboxylates prepared in the presence of structure-directing agents may indeed yield new types of interesting structures with unusual coordination.