Structural chemistry of sulfonated fluorobenzylphosphonate salts. I

A study of the salts of 4-fluoro-3-sulfobenzylphosphonic acid has resulted in the synthesis of two new compounds with unusual layered structures. The crystal structures of these salts and the parent acid have been determined by single crystal X-ray methods. Crystal data: 4-F-3-SO₃H-C₃H₃CH₂PO ₃H₂ · H₂O: triclinic, space group P1̄, Z=2, a = 8.475(2), b = 11.814(2), c = 5.519(1) Å, α = 93.58(1)°, β = 90.47(1)°, γ=88.73(1)°, V=551.4(2) ų, R(F) = 0.037 for 1519 observations (I> 3σ(I)) and 182 variables; [Ni(NH₃)₂(H₂O)₄] ₃(4-F-3-SO₃-C₆H₃-CH ₂PO₃)₂ · 4H₂O: triclinic, space group P1̄, Z = 1, a = 12.998(3), b = 13.050(2), c = 6.217(4) Å, α = 92.68(2)°, β = 93.52(3)°, γ = 79.40(2)°, V = 1033.9(7) ų, R(F) = 0.037 for 2689 observations (I > 3σ(I)) and 511 variables; Na₃(4-F-3-SO₃-C₆H₃CH ₂PO₃) · 8.5H₂O: monoclinic, C2/c, Z = 8, a = 25.636(4), b = 6.218(4), c = 24.136(2) Å, β = 98.33(1)°, V = 3807(3) ų, R(F) = 0.047 for 2262 observations (I> 3σ(I)) and 254 variables. The parent acid monohydrate crystallizes in layers with the acidic groups directed to the faces of the layer. The water molecules are in between the layers hydrogen-bonded to the sulfonate oxygen atoms. The nickel salt contains three independent cations, each of which is hexacoordinated to a mixture of water and ammonia molecules. Thus, there is no direct coordination of the nickel by either the sulfonate or phosphonate oxygen atoms. The structure has alternating layers, the first formed by the anions and one of the nickel complexes, and the second by the other two complexes and the free water molecules. The sodium salt also has the anions arranged in layers but with an interpenetrating three-dimensional network of ionic and hydrogen bonds involving the cations and water molecules. The sodium ions are coordinated to a mixture of sulfonate oxygen atoms and bridging water molecules in irregular six-fold environments. These structures are discussed in terms of the coordination behavior of the difunctional anions in the context of known monofunctional phosphonate and sulfonate compounds.