Di-tert-butyl phosphate as synthon for metal phosphate materials via single-source coordination polymers [M(dtbp)₂]_n (M = Mn, Cu) and [Cd(dtbp)₂(H₂O)]_n (dtbp-H = (tBuO)₂P(O)OH)

Abstract

Reaction of M(OAc)₂·xH₂O (M = Mn, Cu, or Cd) with di-tert-butyl phosphate (dtbp-H) in a 1:2 molar ratio in methanol followed by slow crystallization of the resultant solid in MeOH/THF medium results in the formation of three new polymeric metal phosphates [M(dtbp)₂]_n [M = Mn, 1 (beige); M = Cu, 2 (blue)] and [Cd(dtbp)₂(H₂O)]_n, 3 (colorless)] in good yields. The formation of [Mn(dtbp)₂]_n (1) proceeds via tetrameric manganese phosphate [Mn₄(O)(dtbp)₆] (4), which has been isolated in an analytically pure form. Perfectly air- and moisture-stable compounds 1-4 were characterized with the aid of analytical, thermoanalytical, and spectroscopic techniques. The molecular structures of 1-3 were further established by single-crystal X-ray diffraction studies. Crystal data for 1: C₃₂H₇₂Mn₂O₁₆P₄, monoclinic, P2₁/c, a = 19.957(4) Å, b = 13.419(1) Å, c = 18.083(2) Å, β = 91.25(2)°, Z = 4. Crystal data for 2: C₁₆H₃₆CuO₈P₂, orthorhombic, Pccn, a = 23.777(2) Å, b = 10.074(1) Å, c = 10.090(1) Å, Z = 4. Crystal data for 3: C₄₈H₁₁₄Cd₃O₂₇P₆, triclinic, P_↑, a = 12.689(3) Å, b = 14.364(3) Å, c = 22.491(5) Å, α = 84.54(3)°, β = 79.43(3)°, γ = 70.03(3)°, Z = 2. The diffraction studies reveal three different structural forms for the three compounds investigated, each possessing a one-dimensional coordination polymeric structure. While alternating triple and single dtbp bridges are found between the adjacent Mn²⁺ ions in 1, uniform double dtbp bridges across the adjacent Cu²⁺ ions are present in 2. The cadmium ions in the structure of 3 are pentacoordinated. Thermal analysis (TGA and DSC) indicates that compounds 1-3 convert to the corresponding crystalline metaphosphate materials M(PO₃)₂, in each case at temperatures below 500 °C. Similarly, the thermal decomposition of 4 results in the formation of Mn(PO₃)₃ and Mn₂P₂O₇. The final materials obtained by independent thermal decomposition of bulk samples have been characterized using IR spectroscopic, powder diffraction, and N₂ adsorption studies.