Three-dimensional metal piperazinyldiphosphonate phases with ellipsoidal cavities defined by 44-membered rings: Crystal structures of [M{O₃PCH₂NH(C₂H₄) ₂NHCH₂PO₃}] · H₂O, M = Mn and Co

The hydrothermal reaction of a mixture of (Et₄N)₂MnCl₄, N, N′-piperazinebis(methylenephosphonic acid), Et₄NCl · H₂O, and H₂O in the mole ratio 1:1:5:300, adjusted to pH 5 with 40% aqueous (Bu₄N)OH, at 160°C for 63 h yielded [Mn{O₃PCH₂NH(C₂H₄) ₂NHCH₂PO₃}] · H₂O (1) in 60% as offwhite platelets. The analogous reaction using (Et₄N)₂CoCl₄ produced [Co{O₃PCH₂NH(C₂H₄) ₂NHCH₂PO₃}] · H₂O (2). The isomorphous materials 1 and 2 display three-dimensional network structures, based on binuclear units of corner-sharing metal and phosphorus tetrahedra, forming eight membered {-Co-O-P-O-}₂ rings. The diphosphonate groups serve to tether the binuclear units into large ellipsoidal 44-membered rings. As the piperazinyl nitrogen atoms are protonated, the organic moiety of the disphosphonate group serves as both tether and charge compensating site. Compound 1 exhibits Curie-Weiss paramagnetism with weak antiferromagnetism between Mn centers. In contrast, the susceptibility of 2 exhibits a broad maximum at low temperatures consistent with short range antiferromagnetic coupling. Crystal data: 1, C₆H₁₆MnN₂O₇P₂, triclinic P1, a = 8.393(2)Å, b = 9.043(2)Å, c = 9.125(2)Å, a = 62.88(3)°, β= 86.36(3)°, γ = 78.96(3)°, V = 604.8(3)ų; R = 0.056 for 1663 reflections. 2, C₆H₁₆ CoN₂O₇P₂, triclinic P1, a = 8.340(2)Å, b = 8.917(2)Å, c = 9.018(2)Å, α = 64.11(3)°, γ= 86.24(3)°, γ = 78.87(3)°, V = 591.9(2)ų; R = 0.083 for 1917 reflections.