Crystallization Water Molecules Research Articles

PHYSICO-CHEMICAL CHARACTERISTICS OF MATERIALS BASED ON CERIUM AND CHROMIUM LANTHANOIDES

Some physical and chemical characteristics of hexa(thiocyanate-N)chromate complexes of cerium lanthanides with 3-pyridine-3-carboxylic acid are studied. It was shown by IR spectroscopy for displacement of the main absorption bands that the compounds are N-thiocyanate, the organic ligand is bidentate due to the proton transfer of the carboxyl group to atom nitrogen with the formation of a conjugate system: imino-amine tautomerism of organic ligand leads to the occurrence of pyridinium-3-carboxylic ion. It was established by X-ray diffraction analysis of monocrystals that substances have an isle structure, crystallize according the same structural type, and their crystallographic parameters change regularly in accordance with the change in the radii of Ln3+ ions. The obtained substances of the isle type are isostructural. Iintermolecular hydrogen bonds between crystallization water molecules and N–H groups of coordinated molecules of organic ligands are found. The compositions of the substances differ only in the content of crystallization water in the molecules. Studies of the magnetic properties of the samples were carried out taking into account their stability in the range of 80-360 K. The decomposition sequence is established and composition of thermolysis products. The experimental and calculated values effective magnetic moments is in agreement. Values effective magnetic moments characterize the antiferromagnetic nature of the interaction between paramagnetic centers. At temperatures below 100 K, discrepancies between the experimental and calculated values are observed, which may be due to the transition of compounds from the paramagnetic to antiferromagnetic state. The thermal behavior of substances in an inert atmosphere and oxidizing atmospheres to interval of tempetures 293-1273 K are presented. Compounds obtained determine the promising magnetic and thermal properties of substances as precursors for the low-temperature production of heterometallic oxide ceramic materials, as well as molecular magnets and thermoindicators for visual control of temperatures and temperature fields.

Thermal Studies of Aqueous Free-Base Porphyrin and Metalloporphyrins of Cu, Ag and Mn

Present study is intended on the thermal behaviour of the free base aqueous porphyrin and the corresponding metalloporphyrins of some of the transition metal ions such as Cu, Ag and Mn. The respective porphyrins were synthesized and characterized by ultra violet-visible spectroscopy, infrared spectroscopy and high-resolution mass spectrometry. These porphyrins thus obtained were then subjected to thermal analysis from room temperature to 800 ºC. It was observed that free-base porphyrin tetrasodium meso-tetra (p-sulphonatophenyl) porphyrin (TPPS4) is stable up to 360 ºC and remaining metalloporphyrins are stable in the range of 435-460 ºC, respectively. Further, the hygroscopic porphyrins were subjected to fixation of number of water molecules of crystallization and quantitative analysis with respect to % of metal oxide, % of Na+, % SO4 2- and % coal respectively.

Methyl α-l-sorboside monohydrate.

Methyl l-sorboside monohydrate, C7H14O6·H2O, was prepared from the rare sugar l-sorbose, C6H12O6, and crystallized. It was confirmed that methyl l-sorboside formed α-pyran-ose with a 2 C 5 conformation and crystallized with one water molecule of crystallization. In the crystal, mol-ecules are linked by O-H⋯O hydrogen bonds, forming a three-dimensional network. The unit-cell volume of the title compound, methyl l-sorboside monohydrate, is 481.13 (2) Å3 (Z = 2), which is about 108.16 Å3 (29.0%) greater than that of half the amount of the chemical α-l-sorbose [745.94 (2) Å3 (Z = 4)].

Carbon-free hydrated cobalt vanadium oxide as a promising anode for lithium-ion batteries

Recently, cobalt vanadium oxide (CoV2O6 or CVO), a transition metal-incorporated vanadium oxide, is proposed as a promising anode material for lithium-ion batteries (LIBs). Although introducing cobalt ions into vanadium oxide improves the electrical conductivity and structural stability, gradual structural deterioration compromises the long-term performance of CVO. In this study, hydrated CVO (CoV2O6·4H2O or CVO4H) is synthesized through a simple coprecipitation method, where Li-ion insertion/deinsertion is facilitated in the hydrated structure and the diffusion kinetics are enhanced relative to those of plain CVO. The presence of crystal water molecules in CVO4H increases the interplanar spacing of CVO, enhances the structural stability, and facilitates Li-ion diffusion. To systematically verify these characteristics, various electrochemical analyses (electrochemical impedance spectroscopy, galvanostatic intermittent titration technique, and cyclic voltammetry) are performed. As-synthesized CVO4H exhibits high electrochemical performance (1141/1157 and 1078/1090 mAh g−1 at current densities of 100 and 500 mA g−1 after 200 and 300 cycles) with stable Li-cycling life and good rate capability (capacity retention of ∼70% at 10 A g−1 relative to 0.1 A g−1), without added carbon in the active material. Consequently, CVO4H is a promising candidate material for next-generation LIB anodes.

Synthesis and Selected Properties of New Complex Cation Decorated Polyoxotantalates

Diffusion-based room temperature syntheses using K8{Ta6O19}·16H2O, d-block metal (M) salts (M = Cu, Zn, or Cd), and the macrocyclic ligand 1,4,8,11-tetraazacyclotetradecane (cyclam) led to crystallization of the three new polyoxotantalates with the composition K4{[Cu(cyclam)]2Ta6O19}·18H2O (I), K4{[Zn(cyclam)]2Ta6O19}·18H2O (II), and {[Cd(cyclam)]4Ta6O19}·19H2O (III). The latter two compounds represent the first polyoxotantalates (POTas) with Zn2+ and Cd2+ centered amine complexes and also the first POTas synthesized using a macrocyclic amine. Compounds I and II are isostructural with two complexes attached to the anionic cluster via Cu–O–Ta respectively Zn–O–Ta bonds. Despite that these two compounds are isostructural, the geometry of the M2+ complexes differs significantly with Cu2+ in a square-pyramidal and Zn2+ in a trigonal-bipyramidal environment. In the structure of III, the Cd2+ cations are in the rare hepta-coordinated monocapped trigonal prismatic geometry covalently linked to the anionic core via Cd–O–Ta bonds. While compounds I and II are quite stable under ambient conditions, III shows a fast loss of crystal water molecules. Temperature-dependent in situ XRD measurements were performed with I demonstrating stepwise structural rearrangements caused by water release.

Synthesis and elucidation of binuclear thiazole-based complexes from Co(II) and Cu(II) ions: Conductometry, cytotoxicity and computational implementations for various verifications

A new thiazole-based ligand was prepared and investigated then used to preparing its Co(II) and Cu(II) complexes. All available analytical (CHN analysis & TGA) and spectral (IR, UV–Vis, 1H NMR, Mass, SEM, XRD & EDX) techniques were applied to elucidate the chemical formulae of new compounds. The ligand behaved as a neutral tetradentate towards binuclear metal ions in the two complex via N-H, two C = N and C-S groups. A tetrahedral geometry was suggested for Co(II) complex according to 4A2(F)→4T1(F)(ʋ3) transition at 15,873 cm−1. While, a square-planer geometry was suggested for Cu(II) complex according to 2B1g →2B2g (ʋ1) and 2B1g → 2Eg transitions. The magnetic moment values of the two complexes were appeared lower than the normal values, due to binuclear presence minimized electron spinning. The mass spectra of the complexes recorded their molecular ion peaks that match to the molecular formula after expel of crystal water molecules. A conductometry study was executed for the complex formed from nano-sized CuCl2 and the ligand in solution to extract the association and formation constants as well as the M : L molar ratio. The stereo structures of the ligand and its binuclear complexes were optimized by DFT method under valence double-zeta basis set. The distribution of N(1)-N(10), C(11)-S(12) and C(15)-N(13) groups is suitable for their coordination with the two metal ions without bond strain. The in vitro assay was performed for the new compounds against HePG2, PC3 and MCF-7 cancer cell lines. The two complexes exhibited high toxicity against breast cancer cells. This result was confirmed interestingly via in silico ways as pharmacophore query and MOE-docking. The interaction parameters and docking patterns reflect the superiority of Co(II) and Cu(II) complexes in controlling breast cancer cell which agree with that obtained in vitro.

Synthesis and crystal structure of bis-[μ-N,N-bis-(2-amino-eth-yl)ethane-1,2-di-amine]-bis-[N,N-bis-(2-amino-eth-yl)ethane-1,2-di-amine]-μ4-oxido-hexa-μ3-oxido-octa-μ2-oxido-tetra-oxido-tetra-nickel(II)hexa-tantalum(V) nona-deca-hydrate.

Reaction of K8{Ta6O19}·16H2O with [Ni(tren)(H2O)Cl]Cl·H2O in different solvents led to the formation of single crystals of the title compound, [Ni4Ta6O19(C6H18N4)4]·19H2O or {[Ni2(κ4-tren)(μ-κ3-tren)]2Ta6O19}·19H2O (tren is N,N-bis-(2-amino-eth-yl)-1,2-ethanediamine, C6H18N4). In its crystal structure, one Lindqvist-type anion {Ta6O19}8- (point group symmetry ) is connected to two NiII cations, with both of them coordinated by one tren ligand into discrete units. Both NiII cations are sixfold coordinated by O atoms of the anion and N atoms of the organic ligand, resulting in slightly distorted [NiON5] octa-hedra for one and [NiO3N3] octa-hedra for the other cation. These clusters are linked by inter-molecular O-H⋯O and N-H⋯O hydrogen bonding involving water mol-ecules into layers parallel to the bc plane. Some of these water mol-ecules are positionally disordered and were refined using a split model. Powder X-ray diffraction revealed that a pure crystalline phase was obtained but that on storage at room-temperature this compound decomposed because of the loss of crystal water mol-ecules.

Room Temperature Synthesis of [Pd(cyclam)]5{H3Nb6O19}2 ⋅ 26H2O: a Suitable Precursor for the in‐situ Generation of a Highly Active Catalyst for Light‐Driven Hydrogen Evolution

AbstractThe first Pd2+ containing polyoxoniobate [Pd(cyclam)]5{H3Nb6O19}2 ⋅ 26H2O (I) was prepared at room temperature. In the structure, two hexaniobate clusters are surrounded by a bi‐capped cube formed by Pd2+ centered complexes. This motif is arranged in a layer‐like fashion with crystal water molecules located between cations and anions. Temperature resolved in‐situ X‐ray diffraction experiments demonstrate that successive removal of the crystal water molecules leads to formation of several crystalline intermediate phases. Water sorption investigations show that thermally removed H2O can be successfully reintegrated proceeding via two distinct steps. The catalytic performance for the light‐driven hydrogen evolution reaction (HER) was investigated in a sacrificial system and fluorescein Na+ salt as sensitizer yielding a high value of 90 μmol/h H2. Surprisingly, a composite Pd@Na7[HNb6O19] ⋅ 15H2O is in‐situ formed during the catalytic reaction by cation exchange with simultaneous reduction of Pd2+ nanoparticles decorating the hexaniobate support. The recovered catalyst was even more active producing 157 μmol/h H2 with an apparent quantum efficiency of 1.85 %. Photocatalytic experiments performed with ex‐situ generated Pd nanoparticles deposited on Na7[HNb6O19] ⋅ 15H2O show much lower activities indicating a synergistic effect of the in‐situ generated Pd@Na7[HNb6O19] ⋅ 15H2O catalyst.

Crystal structure of [{[Ni(C10H24N4)][Ni(CN)4]}·2H2O] n , a one-dimensional coordination polymer formed from the [Ni(cyclam)]2+ cation and the [Ni(CN)4]2- anion.

The asymmetric unit of the title compound, catena-poly[[[(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)nickel(II)]-μ-cyanido-κ2 N:C-[bis-(cyanido-κC)nickel(II)]-μ-cyanido-κ2 C:N] dihydrate], {[Ni2(CN)4(C10H24N4)]·2H2O] n or [{[Ni(C10H24N4)][Ni(CN)4]}·2H2O] n , consists of a pair of crystallographically non-equivalent macrocyclic cations and anions. The nickel(II) ions (all with site symmetry ) are coordinated by the four secondary N atoms of the macrocyclic ligands, which adopt the most energetically stable trans-III conformation, and the mutually trans N atoms of the tetra-cyano-nickelate anion in a slightly tetra-gonally distorted NiN6 octa-hedral coordination geometry. The [Ni(CN)4)]2- anion exhibits a bridging function, resulting in the formation of parallel polymeric chains running along the [10] direction. The water mol-ecules of crystallization play a pivotal role in the three-dimensional supra-molecular organization of the crystal. Acting as acceptors, they form N-H⋯Ow (w = water) hydrogen bonds with the secondary amino groups of the macrocycles, forming layers oriented parallel to the (001) plane. At the same time, as donors, they inter-act with the non-coordinated cyano groups of the anion via Ow-H⋯Nc (c = cyanide) hydrogen bonds, giving two-dimensional layers oriented parallel to the (100) plane and thus generating a three-dimensional network.

Ammonium Metatungstate, (NH4)6[H2W12O40]: Crystallization and Thermal Behavior of Various Hydrous Species

Various hydrous ammonium metatungstate phases (NH4)6[H2W12O40]·XH2O (AMT-X) have been obtained in the form of single crystals, using supersaturated solutions, antisolvent crystallization, and partial dehydration as strategies for crystal growth. On the basis of laboratory X-ray diffraction data, the crystal structures of the hydrous phases with X = 22, 12.5, 9.5, 8.5, 6, 4, and 2 as well of the cocrystals with X = 12-ethanol and X = 4-2acetone have been determined for the first time. AMT-22 forms the solid solution series (NH4)6–xKx[H2W12O40]·22H2O with the potassium salt (PMT-22) without a miscibility gap. Its tetragonal crystal structure shows a distorted cubic close-packed arrangement of the spherical α-Keggin-type [H2W12O40]6– anions with disordered ammonium N and water O atoms in the voids. The crystal structures of the other, less-hydrated AMT phases can be derived from distorted hexagonal rod packings of the α-Keggin anions, likewise with the cations and crystal water molecules in the voids. The thermal behavior of AMT-22 crystals reveals a quick dehydration, with AMT-9.5 as an intermediate and AMT-4 as a stable hydrate phase under ambient conditions. Upon further heating, the material decomposes with stepwise formation of AMT-2, AMT-1, AMT-0, and an amorphous phase, before orthorhombic WO3 forms above 400 °C. One of the commercially available AMT phases, “(NH4)6[H2W12O40]·XH2O” (with X = unspecified) has a water content of X = 4 but crystallizes in a structure other than AMT-4. Consequently, the 4-hydrate shows polymorphic behavior.

Synthesis, crystal structure and selected properties of K2[Ni(dien)2]{[Ni(dien)]2Ta6O19}·11 H2O

Abstract The new compound K2[Ni(dien)2]{[Ni(dien)]2Ta6O19}·11 H2O crystallized at room temperature applying a diffusion based reaction in a H2O/DMSO mixture using K8{Ta6O19}·16 H2O, Ni(NO3)2·6H2O and dien (diethylenetriamine). In the crystal structure, the Lindqvist-type anion [Ta6O19]8– is structurally expanded by two octahedrally Ni2+-centered complexes via three Ni–µ 2-O–Ta bonds thus generating the new {[Ni(dien)]2Ta6O19}4– anion. Two KO8 polyhedra share a common edge to form a K2O14 moiety, which connects the {[Ni(dien)]2Ta6O19}4– cluster shells into chains. The isolated [Ni(dien)2]2+ complexes are located in voids generated by the structural arrangement of the chains. An extended hydrogen bonding network between the different constituents generates a 3D network. The crystal water molecules can be thermally removed to form a highly crystalline dehydrated compound. Partial water uptake leads to the formation of a crystalline intermediate with a reduced unit cell volume compared to the fully hydrated sample. Water sorption experiments demonstrate that the fully dehydrated sample can be fully reconverted to the hydrated compound. The crystal field splitting parameters for the octahedrally coordinated Ni2+-centered complexes have been evaluated from an UV/Vis spectrum yielding D q = 1056 cm−1 and B = 887 cm−1.

The Crystal Structures of Two Hydro-closo-Borates with Divalent Tin in Comparison: Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O

Single crystals of Sn(H2O)3[B10H10] · 3 H2O and Sn(H2O)3[B12H12] · 4 H2O are easily accessible by reactions of aqueous solutions of the acids (H3O)2[B10H10] and (H3O)2[B12H12] with an excess of tin metal powder after isothermal evaporation of the clear brines. Both compounds crystallize with similar structures in the triclinic system with space group Pbar{1 } and Z = 2. The crystallographic main features are electroneutral {}_{infty }^{1} {Sn(H2O)3/1[B10H10]3/3} and {}_{infty }^{1} { Sn(H2O)3/1[B12H12]3/3} double chains running along the a-axes. Each Sn2+ cation is coordinated by three water molecules of hydration (d(Sn–O) = 221–225 pm for the B10 and d(Sn–O) = 222–227 pm for the B12 compound) and additionally by hydridic hydrogen atoms of the three nearest boron clusters (d(Sn–H) = 281–322 pm for the B10 and d(Sn–H) = 278–291 pm for the B12 compound), which complete the coordination sphere. Between these tin(II)-bonded water and the three or four interstitial crystal water molecules, classical bridging hydrogen bonds are found, connecting the double chains to each other. Furthermore, there is also non-classical hydrogen bonding between the anionic [BnHn]2− (n = 10 and 12) clusters and the crystal water molecules pursuant to B–Hδ−cdotsδ+H–O interactions often called dihydrogen bonds.

Crystal structure, spectral investigation, thermal properties and evaluation of the antimicrobial behavior of a new 2D polymeric Mn(II): (C6H9N2)2[Mn(C2O4)2].H2O

A new 2D polymeric Mn(II) has been prepared by self-assembly of manganese acetate with oxalic acid and 2-amino-4-picolineand elucidated through single-crystal X-ray diffraction. The complex (C6H9N2)2[Mn(C2O4)2].H2O was considered as a single-chain magnet based on the oxalate linker, intercalated by [C6H9N2]2+ organic cations and one crystallization water molecule that are entrapped between the layers. The Mn(II) ion is coordinated in a slightly distorted octahedral environment by six oxygen atoms belonging to three chelating oxalates. Thermal analysis, FTIR and UV–Vis diffuse reflectance spectroscopy from which the optical properties were determined. The described complex gave antibacterial activity especially against gram-positive bacteria tested species, antifungal activity against Candida albicans specie, as well as lysozyme and anti-biofilm activities.

HYDROGEN BONDS IN THE FORMATION OF COPPER(II) 1,10-PHENANTHROLINE HYDROXYCARBOXYLATOGERMANATE CRYSTALS USING HIRSHFELD SURFACE ANALYSIS

This article is dedicated to the investigation of crystalline structure in the complex cation-anionic compounds Cu(Phen)2Cl]2[Ge(HCit)2]⋅6H2O (I), [Cu(Phen)3]2[Ge2(OH)(HTart)(μ-Tart)2]·11H2O (II), [CuCl(Phen)2]4[{Ge2(OH)2(μ-Tart)2}Cl2]·4Н2О (III), [Cu(Phen)3]2[(OH)2Ge2(μ-HXylar)4Ge2(μ-OH)2]·8H2O (IV), [CuCl(Phen)2]4[(OH)2Ge2(μ-HXylar)4Ge2(μ-OH)2]·8H2O (V) using Hirshfeld surface analysis. This method has showed itself as an effective tool for analysis of intermolecular interactions, such as hydrogen bonds or weaker C…H and С…Н…p connections. Three-dimensional picture of close interactions in the crystal was built for each of the compounds I–V, where short connections are red-colored, while others – weaker and shorter – are light areas and small spots. It was established that in the structures of all compounds different types of hydrogen bonds are presented: bifurcate connections, symmetrical О-Н…О, С-Н…С and asymmetrical ones with water molecules. Two-dimensional histograms – 2D-fingerprint plots, allowed to evaluate quantitively connections in the crystals and establish that H…O/O…H and H…H interactions make the biggest contribution to the total surface area. The presence of the big number of crystallization water molecules is determinant for the formation of complex system of hydrogen bonds and strengthening of the structure, that otherwise would be unstable because of the big size of cations and anions. Due to the fact, that all compounds have the same complexing agent Ge(IV), structure of the anion is determined by polydentate ligand. Obtained results are important for the further development of the water role in the processes of crystallization, crystal formation, electrical dissociation and, especially, dissolving of coordination compounds in biological systems.

Crystal structures of two copper(I)-6,6'-dimethyl-2,2'-bipyridyl (dmbpy) compounds, [Cu(dmbpy)2]2[MF6]·xH2O (M = Zr, Hf; x = 1.134, 0.671).

The syntheses and crystal structures of two bimetallic mol-ecular compounds, namely, bis[bis-(6,6'-dimethyl-2,2'-bi-pyridine)-copper(I)] hexa-fluorido-zir-con-ate(IV) 1.134-hydrate, [Cu(dmbpy)2]2[ZrF6]·1.134H2O (dmbpy = 6,6'-di-methyl-2,2'-bipyri-dyl, C12H12N2), (I), and bis[bis-(6,6'-dimethyl-2,2'-bi-pyr-idine)-copper(I)] hexa-fluorido-hafnate(IV) 0.671-hydrate, [Cu(dmbpy)2]2[HfF6]·0.671H2O, (II), are reported. Apart from a slight site occupany difference for the water mol-ecule of crystallization, compounds (I) and (II) are isostructural, featuring isolated tetra-hedral cations of copper(I) ions coordinated by two dmbpy ligands and centrosymmetric, octa-hedral anions of fluorinated early transition metals. The tetra-hedral environments of the copper complexes are distorted owing to the steric effects of the dmbpy ligands. The extended structures are built up through Coulombic inter-actions between cations and anions and π-π stacking inter-actions between heterochiral Δ- and Λ-[Cu(dmbpy)2]+ complexes. A comparison between the title compounds and other [Cu(dmbpy)2]+ compounds with monovalent and bivalent anions reveals a significant influence of the cation-to-anion ratio on the resulting crystal packing architectures, providing insights for future crystal design of distorted tetra-hedral copper compounds.

Polymorphism of Calcium Decahydrido-closo-decaborate and Characterization of Its Hydrates.

Metal closo-borates and their derivatives have shown promise in several fields of application from cancer therapy to solid-state electrolytes partly owing to their stability in aqueous solutions and high thermal stability. We report the synthesis and structural analysis of α- and β-CaB10H10, which are structurally and energetically similar, both showing a tetrahedral coordination of Ca2+ to four closo-borate cages. The main distinctions between the α- and β-polymorph are found in the crystal system (monoclinic or orthorhombic), topology (wurtzite or cag), and the degree of displacement of Ca2+ from the center of the coordination tetrahedron. Neutron vibrational spectroscopy measurements further revealed distinct perturbations in the cation-anion interactions arising from the different crystal structures. We also synthesized and structurally investigated five stoichiometric hydrates, CaB10H10·xH2O, x = 1, 4, 5, 6, and 7, and discovered an order-disorder polymorphic transition, α- to β-CaB10H10·6H2O. The hydrates reveal a rich structural diversity with ordered structures, CaB10H10·xH2O, x = 1, 4, 5, 6, and 7, as well as disordered structures, x = 6 and 8. The latter allow for a continuum of compositions within 7-8 molecules of crystal water. The DFT-optimized experimental crystal structures reveal complex networks of three types of hydrogen interactions: dihydrogen bonds, B-Hδ-···+δH-O; hydrogen-hydrogen interactions, B-H···H-B; and hydrogen bonds, O-Hδ+···-δO-H. A rather short B-H···H-B (2.14 Å) interaction is observed for CaB10H10·5H2O, which is locally stabilized by four hydrogen bonds.

Puerarin-Na Chelate Hydrate Simultaneously Improves Dissolution and Mechanical Behavior.

Puerarin monohydrate (PUEM), as the commercial solid form of the natural anti-hypertension drug puerarin (PUE), has low solubility, poor flowability, and mechanical properties. In this study, a novel solid form as PUE-Na chelate hydrate was prepared by a reactive crystallization method. Crystal structure analysis demonstrated that PUE-Na contains PUE-, Na+, and water in a molar ratio of 1:1:7. It crystallizes in the monoclinic space group P21, and Na+ is linked with PUE- and four water molecules through Na+ ← O coordination bonds. Another three crystal water molecules occupy channels along the crystallographic b-axis. Observing along the b-axis, the crystal structure features a distinct tubular helix and a DNA-like twisted helix. The complexation between Na+ and PUE- in aqueous solution was confirmed by the Na+ selective electrode, indicating that PUE-Na chelate hydrate belongs to a type of chelate rather than organic metal salt. Compared with PUEM, PUE-Na exhibited a superior dissolution rate (i.e., ∼38-fold increase in water) owing to its lower solvation free energy and clear-enriched exposed polar groups. Moreover, PUE-Na enhanced the tabletability and flowability of PUEM, attributing to its better elastoplastic deformation and lower-friction crystal habit. The unique PUE-Na chelate hydrate with significantly enhanced pharmaceutical properties is a very promising candidate for future product development of PUE.

Synthesis and crystal structures of 3,6-di-hydroxy-picolinic acid and its labile inter-mediate dipotassium 3-hy-droxy-6-(sulfonato-oxy)pyridine-2-carboxyl-ate monohydrate.

A simplified two-step synthesis of 3,6-di-hydroxy-picolinic acid (3-hy-droxy-6-oxo-1,6-di-hydro-pyridine-2-carb-oxy-lic acid), C6H5NO4 (II), an inter-mediate in the metabolism of picolinic acid, is described. The crystal structure of II, along with that of a labile inter-mediate, dipotassium 3-hy-droxy-6-(sulfonato-oxy)pyridine-2-carboxyl-ate monohydrate, 2K+·C6H3NO7S2-·H2O (I), is also described. Compound I comprises a pyridine ring with carboxyl-ate, hydroxyl (connected by an intra-molecular O-H⋯O hydrogen bond), and sulfate groups at the 2-, 3-, and 6-positions, respectively, along with two potassium cations for charge balance and one water mol-ecule of crystallization. These components are connected into a three-dimensional network by O-H⋯O hydrogen bonds arising from the water mol-ecule, C-H⋯O inter-actions and π-π stacking of pyridine rings. In II, the ring nitro-gen atom is protonated, with charge balance provided by the carboxyl-ate group (i.e., a zwitterion). The intra-molecular O-H⋯O hydrogen bond observed in I is preserved in II. Crystals of II have unusual space-group symmetry of type Abm2 in which extended planar networks of O-H⋯O and N-H⋯O hydrogen-bonded mol-ecules form sheets lying parallel to the ac plane, constrained to b = 0.25 (and 0.75). The structure was refined as a 50:50 inversion twin. A minor disorder component was modeled by reflection of the major component across a mirror plane perpendicular to c.

Magnetic Switching in Vapochromic Oxalato-Bridged 2D Copper(II)-Pyrazole Compounds for Biogenic Amine Sensing

A new two-dimensional (2D) coordination polymer of the formula {Cu(ox)(4-Hmpz)·1/3H2O}n (1) (ox = oxalate and 4-Hmpz = 4-methyl-1H-pyrazole) has been prepared, and its structure has been determined by single-crystal X-ray diffraction. It consists of corrugated oxalato-bridged copper(II) neutral layers featuring two alternating bridging modes of the oxalate group within each layer, the symmetric bis-bidentate (μ-κ2O1,O2:κ2O2′,O1′) and the asymmetric bis(bidentate/monodentate) (μ4-κO1:κ2O1,O2:κO2′:κ2O2′,O1′) coordination modes. The three crystallographically independent six-coordinate copper(II) ions that occur in 1 have tetragonally elongated surroundings with three oxygen atoms from two oxalate ligands, a methylpyrazole-nitrogen defining the equatorial plane, and two other oxalate-oxygen atoms occupying the axial positions. The monodentate 4-Hmpz ligands alternatively extrude above and below each oxalate-bridged copper(II) layer, and the water molecules of crystallization are located between the layers. Compound 1 exhibits a fast and selective adsorption of methylamine vapors to afford the adsorbate of formula {Cu(ox)(4-Hmpz)·3MeNH2·1/3H2O}n (2), which is accompanied by a concomitant color change from cyan to deep blue. Compound 2 transforms into {Cu(ox)(4-Hmpz)·MeNH2·1/3H2O}n (3) under vacuum for three hours. The cryomagnetic study of 1–3 revealed a unique switching from strong (1) to weak (2 and 3) antiferromagnetic interactions. The external control of the optical and magnetic properties along this series of compounds might make them suitable candidates for switching optical and magnetic devices for chemical sensing.

Effects of water removal on the structure and spin-crossover in an anilato-based compound

The crucial role played by a crystallization water molecule in the spin crossover (SCO) temperature and its hysteresis is described and discussed in compound [NBu4][Fe(bpp)2][Cr(C6O4Br2)3]⋅2.5H2O (1), where bpp = 2,6-bis(pyrazol-3-yl)pyridine and (C6O4Br2)2− = dianion of the 3,6-dibromo-2,5-dihydroxy-1,4-benzoquinone. The compound has isolated [Fe(bpp)2]2+ cations surrounded by chiral [Cr(C6O4Br2)3]3− anions, NBu4+ cations, and a water molecule H-bonded to one of the non-coordinated N–H groups of one bpp ligand. This complex shows a gradual almost complete two-step spin transition centered at ca. 180 and 100 K with no hysteresis. The loss of the water molecules results in a phase transition from a P21/n phase with only one independent [Fe(bpp)2]2+ cation to a chiral Pn phase with two independent [Fe(bpp)2]2+ cations. Besides, there is an increase in the SCO temperature to 195/202 K with a hysteresis of ca. 7 K. In the dehydrated phase, only one of the two independent [Fe(bpp)2]2+ cations shows the SCO, whereas the second one remains in a high spin configuration at any temperature. In addition, compound 1 exhibits the LIESST (light-induced excited spin-state trapping) effect with a TLIESST of ca. 70 K.