Preparation and Structural Characterization of Two Metallophosphate Frameworks Clathrating Diprotonated Ethylenediamine: AlP0₄-12(en) and GaP0₄-₁₂(en)

Two isostructural framework structures of empirical formula M3(PO4)3-H2O.en, with M = Al, Ga and en = ethylenediamine, have been synthesized as single crystals and characterized by X-ray crystallography. Both compounds crystallize in space group P21/c, Z = 4, with a = 14.542 (2) Å, b = 9.430 (2) Å, c = 9.630 (2) Å, β = 98.21 (1)° and a = 14.656 (2) Å, b = 9.625 (1) Å, c = 9.672 (1) Å, β = 97.90 (1)°, for A1PO4-12 and GaPO4-12, respectively. The structure type is characterized by the intergrowth of sheets, containing alternating corner-linked A1O4 (or GaO4) and PO4 tetrahedra, with slabs containing tetramers composed of Al- (or Ga-) centered trigonal bipyramids cross-linked by PO4 tetrahedra. These building units, infinite in (100), alternate along the a axis and sandwich molecules of diprotonated ethylenediamine between them. Hydrogen atoms are located only on the diprotonated en molecule, C2N2H102+. All oxygen atoms, save one, are linked to at least two (or, in the case of O10 in the tetramer, three) metal atoms. The exception is Ol, bonded to P3 in the sheet. The P3-01 bond is directed toward the en molecule in the cavity between the sheet and the slab and is considerably shorter than other P-O bonds (1.502 (3) Å for GaPO4-12) due to its direct bonding to only P3. Strong hydrogen bonds bind the en molecule to the framework via interactions such as the following: Nl-Hl-Ol, Hl-Ol, 1.78 (1) Å; N1-H2-O7, H2-O7, 1.83 (1) Å.