Hydrothermal Synthesis, Structure Determination, and Magnetic Properties of Three New Copper(II) Methylenediphosphonates with Hybrid Frameworks (MIL-54, 55, 56), and of the Cu Homologue of Na2Co(O3P-CH2-PO3)·(H2O)

The hydrothermal investigation of the quaternary system CuCl 2 ·2H 2 O/methylenediphosphonic acid/NaOH/H 2 O leads to four compounds. Three of them present a new structural type; the fourth is isostructural with a cobalt compound and is already published. Varying experimental parameters such as the initial pH or the temperature allows isolation of each compound as a pure phase. The exception is Cu 2 (O 3 P-CH 2 -PO 3 ) (labeled MIL-54) which presents a dense three-dimensional framework; the three other compounds are built up from layers between which water molecules and/or Na + cations are intercalated. Both MIL-54 and Na 2 Cu(O 3 P-CH 2 -PO 3 )·(H 2 O) are orthorhombic in the space group Pnma (nο. 62) with lattice parameters a = 13.7056(1) Å, b = 7.9953(2) Å, c = 4.9209(1) Å, and V = 539.23(2) Å 3 for MIL-54; in the space group P 2 1 2 1 2 1 (nο. 19), a = 9.0155(2) Å, b = 10.1795(2) Å, c = 16.2084(3) Å, and V = 1487.50(5) Å 3 for Na 2 Cu(O 3 P-CH 2 -PO 3 )·(H 2 O). The two other phases are monoclinic (SG: C 2/ c (nο. 15)) with lattice parameters a = 19.193(1) Å, b = 8.6892(5) Å, c = 9.1904(5) Å, β = 105.858(2)°, and V = 1474.4(1) Å 3, and a = 17.750(4) Å, b = 6.210(1) Å, c = 23.200(5) Å, β = 94.12(3)°, and V = 2550.7(9) Å 3 for Cu 3 (H 2 O) 2 (O 3 P-CH 2 -PO 3 H) 2 ·(H 2 O) (noted MIL-55) and Na 3 Cu 5 (O 3 P-CH 2 PO 3 H x ) 4 ·(H 2 O) 2 ( x = 0.75) (noted MIL-56), respectively. The magnetic behavior of these solids was studied and explained from structural considerations: the three-dimensional MIL-54 and Na 2 Cu(O 3 P-CH 2 -PO 3 )·(H 2 O) exhibit an antiferromagnetic behavior below T N ≈ 45(2) and 50(2) K, respectively, and the other compounds are paramagnetic. Finally, the structural evolution of the title solids depending on the pH is discussed via the connections of trimeric building units.