No abstract

In coordination chemistry and crystal engineering, many factors influence the construction of coordination polymers and the final frameworks depend greatly on the organic ligands used. The diverse coordination modes of N-donor ligands have been employed to assemble metal-organic frameworks. Carboxylic acid ligands can deprotonate completely or partially when bonding to metal ions and can also act as donors or acceptors of hydrogen bonds; they are thus good candidates for the construction of supramolecular architectures. We synthesized under reflux or hydrothermal conditions two new alkaline earth(II) complexes, namely poly[(1,10-phenanthroline-κN,N')bis(μ-3-phenylprop-2-enoato-κO,O':O)calcium(II)], [Ca(CHO)(CHN)], (1), and poly[(1,10-phenanthroline-κN,N')(μ-3-phenylprop-2-enoato-κO:O,O':O')(μ-3-phenylprop-2-enoato-κO,O':O)barium(II)], [Ba(CHO)(CHN)], (2), and characterized them by FT-IR and UV-Vis spectroscopies, thermogravimetric analysis (TGA) and single-crystal X-ray diffraction analysis, as well as by powder X-ray diffraction (PXRD) analysis. Complex (1) features a chain topology of type 2,4 C4, where the Ca atoms are connected by O and N atoms, forming a distorted bicapped trigonal prismatic geometry. Complex (2) displays chains of topology type 2,3,5 C4, where the Ba atom is nine-coordinated by seven O atoms of bridging/chelating carboxylate groups from two cinnamate ligands and by two N atoms from one phenanthroline ligand, forming a distorted tricapped prismatic arrangement. Weak C-H...O hydrogen bonds and π-π stacking interactions between phenanthroline ligands are responsible to the formation of a supramolecular three-dimensional network. The thermal decompositions of (1) and (2) in the temperature range 297-1173 K revealed that they both decompose in three steps and transform to the corresponding metal oxide.

In the title compound, (Ba0.741Sr0.259)C2O4 or C2Ba0.741O4Sr0.259, the asymmetric unit consists of one disordered barium/strontium ion lying on a crystallographic twofold rotation axis and half of a centrosymmetric oxalate ion (one C and two O atoms). The crystal structure can be described as double parallel zigzag chains runnning along the c axis and linked together by additional monodentate oxalate‐metal bonding. The distance between two chains is b/2. Each metal ion has six O‐atom neighbours and they are linked together via the different coordination modes of the oxalate groups, resulting in the formation of a three‐dimensional network.

Considering the low dimensionality of the crystal structure of the known lead squarate tetrahydrate, Pb(C 4 O 4 ).4H 2 O, the thermal reactivity of the powdered compound and structural studies of lower hydrates have been investigated from X-ray single-crystal and powder diffraction data, solid state NMR and thermal analyses. It is shown that Pb(H 2 O)(C 4 O 4 ) and two polymorphs of anhydrous PbC 4 O 4 can be formed within different conditions. Crystal data of the new phases are: Pb(H 2 O)(C 4 O 4 ) (1), S.G. P2 1 /c, a = 7.3650(5) Å, b = 11.302(1) Å, c = 6.6822(4) Å, β= 102.501(6)°, Z = 4; PbC 4 O 4 (2), orthorhombic crystal system, a = 24.276(6) Å, b = 15.261(3) Å, c = 7.850(2) Å, Z = 4; PbC 4 O 4 (3), S.G. I4/mcm, a = 6.1640(2) Å, c = 12.0526(8) Å, Z = 4. The departure of the water molecules leads to the condensation of initial inorganic chains into 2D or 3D-type crystal structures. The full decomposition of the squarate ligand provides successive lead oxides.

In the title coordination polymer, {[Sr(C4HO4)2(H2O)5]·0.5H2O}n, the Sr2+ ion is coordinated by three monodentate hydrogensquarate (hsq) anions and six aqua ligands in a distorted SrO9 monocapped square-anti­prismatic geometry. The hsq anions and water mol­ecules bridge the metal ions into infinite sheets lying parallel to (100). The O atom of the uncoordinated water mol­ecule lies on a crystallographic twofold axis. The packing is stabilized by numerous O—H⋯O hydrogen bonds.