New Reversible Crystal-to-Crystal Conversion of a Mixed-Ligand Lead(II) Coordination Polymer by De- and Rehydration

Synthesis, crystal structures and reversible solid-state crystal-to-crystal transformation of three isostructural lead(ii) halide coordination polymers with different luminescence properties in bulk and nanoscale

Novel isostructural lead(ii) halide CPs have been synthesized in bulk and nanoscale. The compounds exhibited reversible solid-state CTC transformations under mechanochemical reactions. The CPs displayed different thermal and fluorescence properties.

Solvent-assisted structural conversion involving bimetallic complexes based on the tris(oxalato)ferrate(iii) unit with the green → blue → red crystal color sequence

Three new complexes forming a dynamic system and given by the following formulae: [Cu₂(bpy)₄Fe(ox)₃]NO₃·H₂O 1, [Fe(bpy)₃]₂[Fe(ox)₃]NO₃·10H₂O 2 and [Cu(bpy)₃]₂[Fe(ox)₃]NO₃·10H₂O 3 (bpy - 2,2'-bipyridine, ox - oxalate), were synthesized from a methanol-water mixture or water, and characterized structurally, spectroscopically and magnetically. Compound 1 contains trinuclear [(bpy)₂Cu(μ-ox)Fe(ox)(μ-ox)Cu(bpy)₂]⁺ cations, while 2 and 3 can be classified as isomorphous ionic compounds, with alternately arranged hydrophobic and hydrophilic layers of mononuclear complex ions. The green crystals of 1 are perfectly stable in air, whereas in selected solvents they undergo irreversible solvent-assisted recrystallization towards red crystals of 2, which is also accompanied by the appearance of mononuclear blue copper complexes with oxalate, 2,2'-bipyridine and aqua ligands, already described in the literature. The above crystallization/recrystallization processes indicate variable solution contents. The whole effect is accelerated by both the increased temperature and day light irradiation, however, different products from the pool prevail under various conditions. The observed transformation can be understood in terms of thermodynamic and kinetic control, involving the known photo-activity of [Fe(ox)₃]^3- moieties and the effect of quadruple aryl embrace (QAE) on the stability of the crystal network. Considering the presence of Fe^III-ox-Cu^II connectivity in 1 we performed detailed magnetic studies and theoretical calculations for this compound. Due to the strong asymmetry of Cu-O bonds the antiferromagnetic coupling is rather weak, with J_Cu-Fe being ca. -3.4 cm^-1 (using Hamiltonian of the type H = -J_Cu-Fe(S_Cu1S_Fe + S_FeS_Cu2) -J_Cu-Cu(S_Cu1S_Cu2)). We found that these values are very close to those predicted by B3LYP/6-311G* calculations.

Synthesis and characterization of a new nano lead(II) 0-D coordination supramolecular compound: A precursor to produce pure phase nano-sized lead(II) oxide

Nano-structure of a new 0D Pb(II) coordination supramolecular compound, [Pb₄(8-Quin)₆](ClO₄)₂(1), L=8-HQuin=8-hydroxyquinolin ligand has been synthesized by use of a sonochemical process and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy (FTIR) and elemental analyses. The structure of compound 1 was determined by single-crystal X-ray diffraction. The single crystal X-ray data of compound 1 implies that the Pb⁺² ions are five coordinated. Each lead atom is coordinated to nitrogen and oxygen atoms of 8-hydroxyquinolin ligand. Topological analysis shows that the compound 1 is 1,2,3,4,4M12-1net. Nanoparticles of lead(II) oxide have been prepared by calcination of lead(II) coordination polymer at 500°C that were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRPD) and IR spectroscopy.

In situ recrystallization of lanthanide coordination polymers: from 1D ladder chains to 1D linear chains

A rare SCSC transformation for lanthanide coordination polymers is triggered by solvent-mediated isomerization.

Sonochemical syntheses of binuclear lead(II)-azido supramolecule with ligand 3,4,7,8-tetramethyl-1,10-phenanthroline as precursor for preparation of lead(II) oxide nanoparticles

The new neutral binuclear lead(II) azido coordination compound, [Pb ₂(tmph) ₂(μ-N₃)₂(CH₃COO) ₂] (1) [tmph = 3,4,7,8-tetramethyl-1,10-phenanthroline], has been synthesized by a sonochemical method. Single crystal X-ray structure shows that the overall structure of 1 is binuclear unit. Complex 1 has a bridging azido pathway, end-to-end bridging azides between a pair of lead(II) centers. This is further extended into a one-dimensional (1D) and three-dimensional (3D) supramolecular structure by Pb⋯C and π–π weak directional intermolecular interactions. The coordination number of lead(II) ions is seven, PbN₄O₃, with two N-donor atoms from tmph ligands and three O-donors from acetate anions and two N-donors from two azide anions. It has a "stereo-chemically active" electron lone pair, and the coordination sphere is hemidirected. The PbO nanoparticles were obtained by thermolysis of 1 at 180 °C with oleic acid as a surfactant. The morphology and size of the prepared PbO samples were further observed using scanning electron microscopy (SEM).

Thermally induced single crystal to single crystal transformation leading to polymorphism

The robust complex [La(1,10-phen)2(NO3)3] (1,10-phen=1,10-phenanthroline) exhibits thermally induced single crystal to single crystal transformation from one polymorphic phase to another. The complex crystallizes in monoclinic C2/c space group with C2 molecular symmetry at 293K while at 100K it shows P21/c space group with C1 molecular symmetry. Supramolecular investigation shows that at 100K the complex forms 2D achiral sheets whereas at 293K forms two different homochiral 2D sheets. Low temperature DSC analysis indicates that this structural transformation occurs at 246K and also this transformation is reversible in nature. We have shown that thermally induced coherent movement of ligands changes the molecular symmetry of the complex and leads to polymorphism. Photoluminescence property of complex has been studied in both solid state and in methanolic solution at room temperature. The effect of the presence low-lying LUMO orbital of π-character in the complex is elucidated by theoretical calculation using DFT method.

Anion influence on transformations of a nonporous 3D to porous 3D coordination polymer

This work is a new strategy for the preparation of a porous metal–organic framework from a nonporous coordination polymer by a solid state reaction.

A new lead(ii) nanoporous three-dimensional coordination polymer: pore size effect on iodine adsorption affinity

A three-dimensional (3D) nanoporous coordination polymer, [Pb(4-bpdb)(μ-NO₃)(μ-SCN)]_n·1.5CH₃OH (TMU-15), was synthesized. In this compound, we successfully loaded the porous crystals with I₂ by suspending them in a solution of I₂ in cyclohexane.

Sonochemical synthesis of a novel nano-rod two-dimensional zinc(II) coordination polymer; preparation of zinc(II) oxide nanoparticles by direct thermolyses

A novel mixed-ligand zinc(II) coordination polymer, {[Zn(μ-4,4'-bipy)(μ-3-bpdh)(H(2)O)(2)](ClO(4))(2)·(4,4'-bipy)(0.5)}(n) (1); 3-bpdh=2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene and 4,4'-bipy=4,4'-bipyridine, has been synthesized and characterized by IR, (1)HNMR and (13)CNMR spectroscopy. The single crystal X-ray data of compound 1 shows that this coordination polymer grows in two dimensions by two different bridging ligands, 4,4'-bipy and 3-bpdh. Also, nano-scale of compound 1 has been synthesized by sonochemical method and characterized by IR, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Thermal stability of compound 1 in single crystalline and nano-scale form was carried out by thermal gravimetric (TG) and differential thermal analysis (DTA). The ZnO nanoparticles were obtained by calcination of compound 1 at 500°C under air atmosphere and by thermolyses in oleic acid at 200°C. The zinc(II) oxide nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).