A series of microporous coordination polymers of adipic (H 2 ad) and pimelic acids (H 2 pim) with rare earth metals have been synthesized and structurally characterized. In the case of adipic acid, two distinct structure types were isolated: structure type I with formula [Ln 2 -(ad) 3 (H 2 O) 4 ]6H 2 O, Ln ) Ce 3+ , Pr 3+ , Nd 3+ , and strucure type II with formula [Ln 2 (ad) 3 (H 2 O) 4 ]-xH 2 O, Ln ) Nd 3+ , Sm 3+ , Gd 3+ , Er 3+ , Yb 3+ . Type I compounds are isostructural to lanthanum adipate (Inorg. Chem. 1998, 37, 3407) and contain interconnected channels filled with hydrogen-bonded water molecules. The structure of type II polymers consists of interpenetrated (4,4) metal-organic networks. Channels along one crystallographic direction are created by the interpenetration. The minimum width of the channels depends on the nature of the metal incorporated in the framework. The passage from type I to type II structure is ascribed to the well-known effect of lanthanide contraction. In the case of H 2 pim, one compound of formula [La(pim)(Hpim)(H 2 O)]H 2 O was isolated. Channels, filled with water molecules, are formed along one crystallographic direction. In all compounds, the water molecules can be reversibly removed.

The crystal structures have been determined and the magnetic properties investigated for four novel] n 4 the combination of the metal cation with the dicarboxylate ligand leads to the formation of infinitive chains; still the co-ordinated water molecules and the carboxylate oxygen atoms collaborate to hydrogen-bond the chains into 3-D structures. Each cadmium() and nickel() ion in 1 and 4 is coordinated in an octahedral geometry to carboxylate and water molecules. The coordination sphere around copper() ions in 2 is square planar. The structure of 3, [Cu 3 (A) 2 (OH) 2 (H 2 O) 4 ] n , is made up of ribbons linked to neighboring ones by hydrogen bonds. Each ribbon is composed of 2 crystallographically independent metal centers, Cu(1) and Cu(2), which exhibit octahedral and square pyramidal coordination geometries, respectively. Weak antiferromagnetic interactions were observed for 2, and 3 (singlet-triplet energy gap values of Ϫ2.3 and Ϫ54.5 cm Ϫ1 , respectively) and isolated nickel() ions for 4. An interpretation of the magnetic behavior was attempted. The strategy for the assembly of 1-D metal-organic chains into 3-D structures, with the use of coordinated water molecules as hydrogen bond donors and carboxylate oxygens as hydrogen bond acceptors, is also discussed.

Single crystals of [Cd(terephthalate)(H 2 O) 3 ].4H 2 O (1), triaquo(1,4-benzenecarboxylato-O)cadmium tetrahydrate, are grown in a silica gel column. Crystal structure analysis shows that (1) is a polymer with metal-organic chains stacked along the a axis forming layers parallel to the ab plane. These layers are linked by an unusual hydrogen-bonded network formed by the water molecules (both`free' and coordinated ones) and the carboxylate O atoms. This network comprises tridymite-like O 8 cages which`propagate' in the direction of the a axis, mimicking the way they`propagate' along the c axis in hexagonal ice.