Synthesis and Characterization of a Copper(II) Complex with 6-Hydroxypicolinic Acid and 3-Picoline

A copper(II) complex with 6-hydroxypicolinic acid (6-OHpicH) and 3-picoline (3-pic), [Cu(6-OHpic)2(3-pic)2] (1), was prepared by recrystallization of [Cu(6-OHpic)2(H2O)2] from 3-picoline and characterized by IR spectroscopy and thermal methods (TGA/DTA and DSC). The molecular and crystal structure of 1 was determined by single-crystal X-ray structural analysis. The copper(II) ion in 1 has a tetragonally compressed octahedral coordination environment, achieved by two N,O-bidentate 6-hydroxypicolinate ligands and by two 3-picoline molecules in trans positions. The crystal structure of 1 exhibits one strong intermolecular O–HO hydrogen bond, one weak intermolecular C–HO hydrogen bond and one C–Hπ interaction. Molecules of 1 are assembled into a 2D network in the (1 0 –1) plane, giving rise to C11(8) graph-set motif. These 2D networks are further assembled into 3D architecture only by weak Van der Waals interactions. A thermogravimetric study showed the initial loss of two coordinated 3-picoline molecules in 1, followed by a complete decomposition of the compound. (doi: 10.5562/cca2119

Hardy's Inequality for the fractional powers of Grushin operator

We prove Hardy's inequality for the fractional powers of the generalized sublaplacian and the fractional powers of the Grushin operator. We also find an integral representation and a ground state representation for the fractional powers of generalized sublaplacian

Chalcogen S∙∙∙S Bonding in Supramolecular Assemblies of Cadmium(II) Coordination Polymers with Pyridine-Based Ligands

Two cadmium(II) coordination polymers, with thiocyanate and pyridine-based ligands e.g., 3- acetamidopyridine (3-Acpy) and niazid (nicotinic acid hydrazide, nia), namely one- dimensional {; ; [Cd(SCN)2(3-Acpy)]}; ; n (1) and two- dimensional {; ; [Cd(SCN)2(nia)]}; ; n (2), are prepared in the mixture of water and ethanol. The adjacent cadmium(II) ions in 1 are bridged by two N, S-thiocyanate ions and an N, O-bridging 3-Acpy molecule, forming infinite one- dimensional polymeric chains, which are assembled by the intermolecular N–H∙∙∙S hydrogen bonds in one direction and by the intermolecular S∙∙∙S chalcogen bonds in another direction. Within the coordination network of 2, the adjacent cadmium(II) ions are bridged by N, S-thiocyanate ions in one direction and by N, O, N’-chelating and bridging nia molecules in another direction. The coordination networks of 2 are assembled by the intermolecular N–H∙∙∙S and N–H∙∙∙N hydrogen bonds and S∙∙∙S chalcogen bonds. Being the only supramolecular interactions responsible for assembling the polymer chains of 1 in the particular direction, the chalcogen S∙∙∙S bonds are more significant in the structure of 1, whilst the chalcogen S∙∙∙S bonds which act in cooperation with the N–H∙∙∙S and N–H∙∙∙N hydrogen bonds are of less significance in the structure of 2

Structural and Electrochemical Studies of Cobalt(II) and Nickel(II) Coordination Polymers with 6-Oxonicotinate and 4,4′-Bipyridine

The 6-oxonicotinate (6-Onic) salts of a one-dimensional cationic cobalt(II) or nickel(II) coordination polymers with 4,40 -bipyridine (4,40 -bpy), namely {[Co(4,40 -bpy)(H2O)4 ](6-Onic)2 ·2H2O}n (1) and {[Ni(4,40 -bpy)(H2O)4 ](6-Onic)2 ·2H2O}n (2), were prepared hydrothermally by reactions of cobalt(II) nitrate hexahydrate or nickel(II) nitrate hexahydrate, respectively, 6-hydroxynicotinic acid and 4,40 -bipyridine in a mixture of ethanol and water. In the hydrogen-bonded frameworks of 1 and 2, the one-dimensional polymeric chains of {[M(4,40 -bpy)(H2O)4 ] 2+}n (M = Co, Ni), the 6-oxonicotinate anions and the lattice water molecules were assembled via strong intermolecular O–H···O and N–H···O hydrogen bonds and π–π interactions, leading to the formation of the representative hydrogen-bond ring motifs: trimeric R 2 3 (10) motif, the centrosymmetric tetrameric R 2 4 (8) and R 2 4 (12) motifs and the pentameric R 4 5 (12) motif. The isostructural coordination polymers 1 and 2 exhibited a different electrochemical behavior, as observed by cyclic voltammetry, which can be attributed to the nature of the metal ions (cobalt(II) vs. nickel(II))

The Solvent Effect on Composition and Dimensionality of Mercury(II) Complexes with Picolinic Acid

Three new mercury(II) coordination compounds, {[HgCl(pic)]}n (1), [HgCl(pic)(picH)] (2), and [HgBr(pic)(picH)] (3) (picH = pyridine-2-carboxylic acid, picolinic acid) were prepared by reactions of the corresponding mercury(II) halides and picolinic acid in an aqueous (1) or alcohol–methanol or ethanol (2 and 3) solutions. Two different types of coordination compounds were obtained depending on the solvent used. The crystal structures were determined by the single-crystal X-ray structural analysis. Compound 1 is a one-dimensional (1-D) coordination polymer with mercury(II) ions bridged by chelating and bridging N,O,O′-picolinate ions. Each mercury(II) ion is four-coordinated with a bidentate picolinate ion, a carboxylate O atom from the symmetry-related picolinate ion and with a chloride ion; the resulting coordination environment can be described as a highly distorted tetrahedron. Compounds 2 and 3 are isostructural mononuclear coordination compounds, each mercury(II) ion being coordinated with the respective halide ion, N,O-bidentate picolinate ion, and N,O-bidentate picolinic acid in a highly distorted square-pyramidal coordination environment. Compounds 1–3 were characterized by IR spectroscopy, PXRD, and thermal methods (TGA/DSC) in the solid state and by 1H and 13C NMR spectroscopy in the DMSO solution

The Anion Impact on Dimensionality of Cadmium(II) Complexes with Nicotinamide

Three novel cadmium(II) coordination compounds, the dimeric [Cd(CH3COO)2(nia)2]2 (1), the polymeric {[Cd(nia)4](ClO4)2}n (2), and the monomeric [Cd(H2O)3(nia)3](ClO4)2·nia (3), were prepared in the reactions of the nicotinamide (pyridine-3-carboxamide, nia) with the corresponding cadmium(II) salts. All prepared compounds were characterized by elemental analyses, FT-IR spectroscopy, TGA/DTA, and single crystal X-ray analysis. The impact of anions (acetate, perchlorate) and solvent used on the dimensionality of cadmium(II) complexes and the cadmium(II) coordination environment was investigated. The bridging capabilities of acetate ions enabled the formation of dimers in the crystal structure of 1. It was shown that the dimensionality of perchlorate complexes depends on the solvent used. The coordination polymer 2 is isolated from an ethanol solution, while monomeric compound 3 was obtained by using a water/ethanol mixture as a solvent. The pentagonal-bipyramidal coordination of cadmium(II) was found in the presence of chelating and bridging acetate ions in 1. In the presence of non-coordinating perchlorate anions in 2 and 3, the coordination geometry of cadmium(II) is found to be octahedral. The supramolecular amide-amide homosynthon R22(8) was preserved in the hydrogen-bonded frameworks of all three compounds

Structural and DFT Studies on the Polymorphism of a Cadmium(II) Dipicolinate Coordination Polymer

The coordination polymer [Cd₂(dipic)₂(H₂O)₃]_<i>n</i> was prepared by the reaction of cadmium­(II) chloride or bromide and dipicolinic acid (dipicH₂) at 60 °C under autogenous pressure. The <i>C</i>2/<i>c</i> polymorph (<b>1</b>) was almost exclusively obtained. However, a few crystals of the <i>P</i>2/<i>c</i> polymorph (<b>2</b>) were occasionally found in the mixture with the <i>C</i>2/<i>c</i> polymorph, thus making it a disappearing and concomitant polymorph. The polymeric chains in <b>1</b> are connected into dimers by π–π interaction and O–H···O hydrogen bonds. These dimers are in turn connected by intermolecular O–H···O hydrogen bonds into a 2D network. The polymeric chains in <b>2</b> are connected by intermolecular O–H···O hydrogen bonds into a zigzag chain along the [001] direction. According to DFT calculations, the hydrogen bonding is of similar order in both polymorphs (∼7.5 kcal mol^–1 per hydrogen bond). However, there is additional stability imparted in <b>1</b>, as shown by dispersion-corrected DFT, through π–π stacking between polymeric chains, making <b>1</b> the thermodynamically favored polymorph. Polymorph <b>1</b> was characterized by IR spectroscopy, PXRD analysis, and TGA and DSC methods. The DSC analysis did not show any sign of phase transition between <b>1</b> and <b>2</b>. This was also confirmed by variable temperature PXRD, since the pattern of <b>1</b> remained unchanged until the decomposition of <b>1</b>

Structural and DFT Studies on the Polymorphism of a Cadmium(II) Dipicolinate Coordination Polymer

The coordination polymer [Cd₂(dipic)₂(H₂O)₃]_<i>n</i> was prepared by the reaction of cadmium­(II) chloride or bromide and dipicolinic acid (dipicH₂) at 60 °C under autogenous pressure. The <i>C</i>2/<i>c</i> polymorph (<b>1</b>) was almost exclusively obtained. However, a few crystals of the <i>P</i>2/<i>c</i> polymorph (<b>2</b>) were occasionally found in the mixture with the <i>C</i>2/<i>c</i> polymorph, thus making it a disappearing and concomitant polymorph. The polymeric chains in <b>1</b> are connected into dimers by π–π interaction and O–H···O hydrogen bonds. These dimers are in turn connected by intermolecular O–H···O hydrogen bonds into a 2D network. The polymeric chains in <b>2</b> are connected by intermolecular O–H···O hydrogen bonds into a zigzag chain along the [001] direction. According to DFT calculations, the hydrogen bonding is of similar order in both polymorphs (∼7.5 kcal mol^–1 per hydrogen bond). However, there is additional stability imparted in <b>1</b>, as shown by dispersion-corrected DFT, through π–π stacking between polymeric chains, making <b>1</b> the thermodynamically favored polymorph. Polymorph <b>1</b> was characterized by IR spectroscopy, PXRD analysis, and TGA and DSC methods. The DSC analysis did not show any sign of phase transition between <b>1</b> and <b>2</b>. This was also confirmed by variable temperature PXRD, since the pattern of <b>1</b> remained unchanged until the decomposition of <b>1</b>