Hybrid open frameworks (MIL-n). Part 4 Synthesis and crystal structure of MIL-8, a series of lanthanide glutarates with an open framework, [Ln(H2O)]2[O2C(CH2)3CO2]3·4H2O

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Abstract
The first series of rare-earth carboxylates with an open framework has been prepared hydrothermally (180°C, 3 days) by the action of glutaric acid on the metal chlorides in the presence of base. The crystal structure of the neodymium compound [Nd III (H 2 O)] 2 [O 2 C(CH 2 ) 3 CO 2 ] 3 ·4H 2 O has been determined by single-crystal X-ray diffraction. The composite material crystallizes in the monoclinic space group C2/c (no. 15) with a=8.1174(1) Å, b=15.1841(3) Å, c=19.8803(3) Å, β=93.762(1)° (final agreement factors R 1 =0.0279, wR 2 =0.0693). The organic-inorganic network is three-dimensional and consists of chains of edge-sharing rare-earth polyedra NdO 8 (H 2 O) along the [100] direction, linked together by the carbon chains along two directions. The connection involves the formation of channels parallel to the rare-earth chains in which weakly bonded water molecules are incorporated. The analogous compounds were obtained with Pr, Sm, Eu, Gd, Dy, Ho and Y.