ORIGINAL PAPER A new neodymium(III)–calcium(II) one-dimensional coordination polymer constructed from dipicolinic acid: synthesis, crystal structure, spectroscopic and thermal analysis, and solution studies Mohammad Ghadermazi • Zohreh Derikvand • Arezoo Zahedi • Ardeshir Shokrollahi • Sara Nasiri • Hadi Amiri Rudbari Received: 20 April 2014 / Accepted: 30 November 2014 Ó Springer-Verlag Wien 2014 Abstract A new heterometallic supramolecular coordi- nation polymer, namely [(1-mimH)[Nd(pydc) 3 Ca(pydcH 2 ) (H 2 O) 2 ]4H 2 O] n (where pydcH 2 = pyridine-2,6-dicarbox- ylic acid (dipicolinic acid), 1-mim = 1-methylimidazole) has been prepared and characterized by elemental analysis, spectral (IR, UV–Vis), 1 H NMR and 13 C NMR spectros- copy, thermal analysis as well as single-crystal X-ray diffraction. The X-ray diffraction study demonstrates that the compound has a 1D network; the layers of this com- pound are connected by complicated hydrogen bonds to form 3D supramolecular architecture. The polymeric chain contains Nd(III) ions and Ca(II) ions bridged by (pydc) 2- ligands. Each (pydc) 2- ion is connected to one neodym- ium(III) ion as a tridentate ligand and one calcium ion via bridging carboxylate group. The equilibrium constants of dipicolinic acid and 1-methylimidazole, pydc/1-mim pro- ton transfer system, as well as those of the complexes (binary, ternary, and quaternary) were investigated by potentiometric pH titration method. Keywords Nd–Ca compound  Coordination polymer  Crystal structure  Methylimidazole Introduction Metal-organic frameworks (MOFs) constructed from metal ions and organic bridging ligands under appropriate con- ditions, are of interest due to their tremendous potential applications in many fields, such as luminescence, cataly- sis, nonlinear optics, gas storage, ion exchange, and molecular magnetism [1–12]. In general, the construction of charming structural topologies immensely depends on the organic ligands and the coordination geometry of central metal ions [13–16]. The bidentate or multidentate bridging ligands containing N- or O-donors are used to bind metal centers, generating 1D, 2D, and 3D coordina- tion polymers. Hence, the selection of suitable organic ligands is critical for constructing coordination architec- tures. Among the organic ligands, the versatile multicarboxyl compounds [17, 18] especially the dipicoli- nic acid and its deprotonated anions (Hpydc - and pydc 2- appropriate pH value) which adopt flexible, mul- tidentate coordination sites, and therefore may potentially provide various coordination modes which are beneficial to the construction of higher-dimensional Ln-MOFs [19–25]. In our ongoing investigation on the coordination chemistry of dipicolinic complexes, herein we describe the synthesis, spectroscopic, elemental and thermal analysis, crystal structures, and solution studies of a novel one-dimensional Electronic supplementary material The online version of this article (doi:10.1007/s00706-014-1377-4) contains supplementary material, which is available to authorized users. M. Ghadermazi (&)  A. Zahedi Department of Chemistry, Faculty of Science, University of Kurdistan, Sanandaj, Iran e-mail: mghadermazi@yahoo.com Z. Derikvand Department of Chemistry, Faculty of Science, Khorramabad Branch, Islamic Azad University, Khorramabad, Iran A. Shokrollahi Department of Chemistry, Yasouj University, Yasouj, Iran H. A. Rudbari Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran S. Nasiri Department of Science and Research branch, Islamic Azad University, Fars, Iran 123 Monatsh Chem DOI 10.1007/s00706-014-1377-4