| Coordination polymers of lanthanides have been synthesized by using various ligands such as tartaric acid, oxalic acid, squaric acid (SA) and isonicotinic acid (INA). Oxalate ligand was introduced in the coordination polymers directly as well as through in-situ derivation from tartaric acid by using iodide ion as the reducing agent. When mixed ligands were introduced with the lanthanides, the D and L varieties of tartaric acid exhibit partial separation in the crystal lattice around the other ligand. INA ligand having both N and O sites for coordination facilitates the bonding of lanthanides with transition metals on the basis of HSAB theory. All the coordination polymers have been synthesized by hydrothermal method and characterized by single crystal X-ray diffraction analysis. The IR spectra and thermogravimetric behavior of the compounds have also been studied.Five coordination polymers with the formula [Ln2(C4H4O6)3(H2O)3]·1.5H2O, where Ln = La (1), Ce (2), Pr (3), Nd (4) and Sm (5), have been synthesized in the category of lanthanide tartrate compounds. These compounds are isomorphic and crystallize in monoclinic crystal system with P21/n space group. The metal center is trivalent and coordinated to nine oxygen atoms. The crystal structure has three-dimensional framework, which has open channels containing non-coordinated water molecules. This structure of coordination polymers of lanthanides with tartaric acid have been reported for the first time.Three coordination polymers have been prepared in the category of lanthanide oxalates. Compound 6, [Pr2(C2O4)3(H2O)4]·2H2O, and compound 7, [Nd2(C2O4)3(H2O)4]·2H2O, crystallize in monoclinic crystal system with P21/c space group and triclinic crystal system with Pīspace group respectively. Both have three-dimensional crystal lattice and their structures vary in presence of different number of oxo bridges and the position of the coordinated water molecules bonded to the metal atoms. Compound 8, [Pr2(C2O4)3(H2O)6]·3H2O, has well known two-dimensional honey-comb crystal lattice and crystallizes in monoclinic crystal system with P21/c space group. This compound has been produced in an unusual way by the in-situ hydrothermal degradation of tartaric acid to oxalate ions in presence of KI. The role of iodide anion as reducing agent towards the reductive coupling of CO2 has not been reported yet.Five new compounds have been prepared by using lanthanides and mixed ligands having carbonyl functionality. Two combinations of oxalic acid with D-L tartaric acid and squaric acid with D-L tartaric acid were selected to coordinate with lanthanides. The motive to separate the D and L varieties of tartaric acid has been partially successful as the two enantiomers of tartaric acid have been arranged in different layers separated by the oxalate or SA ligands in the coordination polymers. Compound 9, [Pr(C4H4O6)(C2O4)1/2(H2O)]·1.5H2O crystallize in monoclinic crystal system, P21/c space group having three-dimensional crystal lattice. Compound 10, [Nd(C4H4O6)(C2O4)1/2(H2O)2], and 11, [Sm(C4H4O6)(C2O4)1/2(H2O)]·1.5H2O, are isomorphous and crystallizes in triclinic crystal system, Pīspace group having two-dimensional crystal lattice. Compound 12, [Pr(C4H4O6)(C4O4)1/2(H2O)3]·H2O, and Compound 13, [Nd(C4H4O6)(C4O4)1/2(H2O)3]·H2O, are also isomorphous to each other and crystallize in triclinic crystal system, Pīspace group having one-dimensional crystal lattice. It has been seen that the dimensionality of this series of compounds is influenced by the involvement of the terminal carboxylate oxygen atoms of tartaric acid in coordinating with metal.A new coordination polymer of the category of coordination polymers having hetero metal atoms with mixed ligands has been synthesized. Pr and Cu metals have been coordinated together through the linking of oxalate and INA ligands. The basic idea of HSAB theory has been implemented to join the transition metals like Cu through N site with the lanthanides like Pr through O site of the ligands. The compound 14, [PrCu(C6H4NO2)2(C2O4)]·H2O, has been synthesized in this way. It crystallizes in monoclinic crystal system, C2/c space group having three-dimensional crystal lattice. Cu has 1+ oxidation state and the crystals have orange yellow color. An important feature of the compound is the formation of double bridges between two Pr atoms through the oxygen atoms of INA ligands. Formation of such bridges and involvement of Cu in the Pr network have potential applications towards the magnetic behavior of the coordination polymers.
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