Non-coordinated Water Molecules Research Articles

A Gadolinium(III) Complex Based on Pyridoxine Molecule with Single-Ion Magnet and Magnetic Resonance Imaging Properties.

Pyridoxine (pyr) is a versatile molecule that forms part of the family of B vitamins. It is used to treat and prevent vitamin B6 deficiency and certain types of metabolic disorders. Moreover, the pyridoxine molecule has been investigated as a suitable ligand toward metal ions. Nevertheless, the study of the magnetic properties of metal complexes containing lanthanide(III) ions and this biomolecule is unexplored. We have synthesized and characterized a novel pyridoxine-based GdIII complex of formula [GdIII(pyr)2(H2O)4]Cl3 · 2 H2O (1) [pyr = pyridoxine]. 1 crystallizes in the triclinic system and space group Pī. In its crystal packing, cationic [Gd(pyr)2(H2O)4]3+ entities are connected through H-bonding interactions involving non-coordinating water molecules and chloride anions. In addition, Hirshfeld surfaces of 1 were calculated to further investigate their intermolecular interactions in the crystal lattice. Our investigation of the magnetic properties of 1, through ac magnetic susceptibility measurements, reveals the occurrence of a slow relaxation in magnetization in this mononuclear GdIII complex, indicating an unusual single-ion magnet (SIM) behavior for this pseudo-isotropic metal ion at very low temperatures. We also studied the relaxometric properties of 1, as a potential contrast agent for high-field magnetic resonance imaging (MRI), from solutions of 1 prepared in physiological serum (0.0-3.2 mM range) and measured at 3 T on a clinical MRI scanner. The values of relaxivity obtained for 1 are larger than those of some commercial MRI contrast agents based on mononuclear GdIII systems.

Crystal structure and characterization of a new lanthanide coordination polymer, [Pr2(pydc)(phth)2(H2O)3]·H2O

A new lanthanide coordination polymer, poly[[triaquabis(μ4-phthalato)(μ3-pyridine-2,5-dicarboxylato)dipraseodymium] monohydrate], {[Pr2(C7H3NO4)2(C8H4O4)(H2O)3]·H2O} n or {[Pr2(phth)2(pydc)(H2O)3]·H2O} n , (pydc2− = pyridine-2,5-dicarboxylate and phth2− = phthalate) was synthesized and characterized, revealing the structure to be an assembly of di-periodic {Pr2(pydc)(phth)2(H2O)3} n layers. Each layer is built up by edge-sharing {Pr2N2O14} and {Pr2O16} dimers, which are connected through a new coordination mode of pydc2− and phth2−. These layers are stabilized by internal hydrogen bonds and π–π interactions. In addition, a three-dimensional supramolecular framework is built by interlayer hydrogen-bonding interactions involving the non-coordinated water molecule. Thermogravimetric analysis shows that the title compound is thermally stable up to 400°C.

Tetra-aqua-(ethane-1,2-di-amine-κ2N,N')nickel(II) naphthalene-1,5-di-sulfonate dihydrate.

The reaction of ethane-1,2-di-amine (en, C2H8N2), the sodium salt of naphthalene-1,5-di-sulfonic acid (H2NDS, C10H8O6S2), and nickel sulfate in an aqueous solution resulted in the formation of the title salt, [Ni(C2H8N2)(H2O)4](C10H6O6S2)·2H2O or [Ni(en)(H2O)4](NDS)·2H2O. In the asymmetric unit, one half of an [Ni(en)(H2O)4]2+ cation and one half of an NDS2- anion, and one water mol-ecule of crystallization are present. The Ni2+ cation in the complex is positioned on a twofold rotation axis and exhibits a slight tetra-gonal distortion of the cis-NiO4N2 octa-hedron, with an Ni-N bond length of 2.0782 (16) Å, and Ni-O bond lengths of 2.1170 (13) Å and 2.0648 (14) Å. The anion is completed by inversion symmetry. In the extended structure, the cations, anions, and non-coordinating water mol-ecules are connected by inter-molecular N-H⋯O and O-H⋯O hydrogen bonding, as well as C-H⋯π inter-actions, forming a three-dimensional network.

Synthesis, crystal structure, stereochemical and Hirshfeld surface analysis of trans-di-aqua-bis-(1-phenyl-propane-1,2-di-amine-κ2N,N')nickel(II) dichloride dihydrate.

In the hydrated complex salt, [Ni(C9H14N2)2(H2O)2]Cl2·2H2O, the asymmetric unit comprises of half of the complex cation along with one chloride anion and one non-coordinating water mol-ecule. The central nickel(II) atom is located on an inversion center and is coordinated in a trans octa-hedral fashion by four N atoms from two bidentate 1,2-di-amino-1-phenyl-propane ligands in the equatorial plane, and by two oxygen atoms from two water mol-ecules occupying the axial sites. The five-membered chelate ring is in a slightly twisted envelope conformation. The crystal packing features O-H⋯Cl, N-H⋯O and N-H⋯Cl hydrogen bonds. Hirshfeld surface analysis revealed that the most important contributions to the crystal packing are from H⋯H (56.4%), O⋯H/H⋯O (16.4%) and H⋯Cl (13.3%) inter-actions. The crystal void volume was calculated to be 15.17%.

Pressure-Induced Coordination Number Transition in Lanthanide Mellitate Coordination Polymers: Structure and Spectroscopy.

High external pressure is found to induce a non-coordinated water molecule to bond to cerium in a previously studied mellitate coordination polymer, as determined by high-pressure single-crystal X-ray diffraction, resulting in a coordination number transition at 3.85 GPa from 9 to 9.5 where half the cerium ions are 10-coordinate. Also, bond length changes due to increased pressure are experimentally measured, whereas the cerium-carboxylate bond lengths overall change by -0.004(9) Å/GPa, the cerium-water bonds by -0.016(3) Å/GPa, and cerium-oxygen bonds overall by -0.010(6) Å/GPa, which corresponds well with theoretical bond length decreases determined for similar compounds. The high-pressure absorbance spectra of the analogous neodymium mellitate are examined and compared with the structural changes observed.

A Series of Novel 3D Coordination Polymers Based on the Quinoline-2,4-dicarboxylate Building Block and Lanthanide(III) Ions-Temperature Dependence Investigations.

A series of novel 3D coordination polymers [Ln2(Qdca)3(H2O)x]·yH2O (x = 3 or 4, y = 0-4) assembled from selected lanthanide ions (Ln(III) = Nd, Eu, Tb, and Er) and a non-explored quinoline-2,4-dicarboxylate building block (Qdca2- = C11H5NO42-) were prepared under hydrothermal conditions at temperatures of 100, 120, and 150 °C. Generally, an increase in synthesis temperature resulted in structural transformations and the formation of more hydrated compounds. The metal complexes were characterized by elemental analysis, single-crystal and powder X-ray diffraction methods, thermal analysis (TG-DSC), ATR/FTIR, UV/Vis, and luminescence spectroscopy. The structural variety of three-dimensional coordination polymers can be ascribed to the temperature effect, which enforces the diversity of quinoline-2,4-dicarboxylate ligand denticity and conformation. The Qdca2- ligand only behaves as a bridging or bridging-chelating building block binding two to five metal centers with seven different coordination modes arising mainly from different carboxylate group coordination types. The presence of water molecules in the structures of complexes is crucial for their stability. The removal of both coordinated and non-coordinated water molecules leads to the disintegration and combustion of metal-organic frameworks to the appropriate lanthanide oxides. The luminescence features of complexes, quantum yield, and luminescent lifetimes were measured and analyzed. Only the Eu complexes show emission in the VIS region, whereas Nd and Er complexes emit in the NIR range. The luminescence properties of complexes were correlated with the crystal structures of the investigated complexes.

Three new zinc(II) 4′-chloro-2,2′:6′,2ʺ-terpyridine (4′-Cltpy)-based complexes: synthesis, spectroscopic and structural studies, thermal behavior, and Hirshfeld surface analysis

Three new ZnII complexes with the ligand 4′-chloro-2,2′:6′,2ʺ-terpyridine (4′-Cltpy), [Zn(4′-Cltpy)(N3)2] (1), [Zn(4′-Cltpy)(NCS)2] (2) (two 1:1 metal/ligand complexes) and a 1:2 metal/ligand complex, [Zn(4′-Cltpy)2](NO3)2·2H2O (3), have been synthesized and characterized by elemental analysis, IR, 1H NMR spectroscopy and single-crystal X-ray diffraction. The structures of 1 and 2 contain a ZnN5 coordination sphere, which includes coordination from three nitrogen donors of the 4′-Cltpy ligand and two nitrogen atoms of two terminal azide or two terminal thiocyanate ligands, respectively. Addison’s τ value suggests a distorted square pyramidal coordination of ZnII in 1 and intermediate between square pyramidal and trigonal bipyramidal in 2. In the complex cation of 3, the ZnII center is coordinated by six nitrogen atoms from two 4′-Cltpy ligands in a distorted octahedral coordination geometry. In this structure, two non-coordinating nitrate anions serve as counterions, and there are two non-coordinating solvent water molecules. Hirshfeld surface analysis was employed to clarify the nature and extent of intermolecular interactions. In addition, the thermal stabilities of the compounds were evaluated by thermogravimetric analysis (TGA).

Synthesis, crystal structure and spectroscopic investigations of heteronuclear Co(III)/Cu(II), Co(III)/Cd(II) and Fe(III)/Cd(II) 3D coordination polymers with 4-(2-aminoethyl)pyridine

The cyanide complexes of transition metals with 4-(2-aminoethyl)pyridine (4aepy) of {[Cu(H2O)(µ-4aepy)Cu(µ-4aepy)2Cu(µ-4aepy)Co2(µ-CN)6(CN)6]·3H2O}n (1), (NH4)[Cd(µ-4aepy)2Co(µ-CN)2(CN)4]n (2) and (NH4)[Cd(µ-4aepy)2Fe(µ-CN)2(CN)4]n (3) were synthesized and investigated by vibrational (FT-IR and Raman), powder X-ray diffraction (PXRD), elemental and thermal analysis techniques. The crystal structures of the complexes have been determined by the single crystal X-ray diffraction (SC-XRD) patterns. The crystallographic analysis reveals that complex 1 crystallizes in the monoclinic system, space group P21, whereas; complexes 2 and 3 crystallize in the tetragonal system, space group P42/ncm. The asymmetric unit of heterometallic complex 1 consists of three Cu(II) ions, two Co(III) ions, four 4aepy ligands, twelve cyanide ligands, one aqua ligand and three non-coordinated water molecules. The asymmetric unit of heterometallic complexes 2–3 consists of one Cd(II) ion, one M ion [M = Co(III) in 2 and Fe(III) in 3], two cyanide ligands, half 4aepy ligand and one ammonium ion. Each Cd(II) ion is located at a center of symmetry and is coordinated by two nitrogen atoms by the cyanide ligands and by four nitrogen atoms by the 4aepy ligands. As a result, they show distorted octahedral coordination geometries. In complex 1, the intermolecular O–H⋯N, N–H⋯N, N–H⋯O and C–H⋯N hydrogen bonds and CN⋯π and π⋯π interactions play a crucial role in the architecture of 3D network. The intermolecular CN···π interaction between cyanide ligand and pyridine ring of the 4aepy ligand is the most striking feature of complex 1. Heterometallic complexes 2–3 have 3D coordination polymers.

Synthesis, characterization, Hirshfeld surface analysis and DFT study of a new ionic Co(II) complex with 2,4,6-tris(2-pyridyl)-1,3,5-triazine

• [Co(tptz) Cl(H 2 O) 2 ]Cl. 5.5 H 2 O where tptz is 2,4,6-tris(2-pyridyl)-1,3,5-triazine has been • synthesized. • Intermolecular interactions were investigated by Hirshfeld surfaces. • Electronic properties such as HOMO and LUMO energies were derived A new complex compound [Co(tptz)Cl(H 2 O) 2 ]Cl.5.5H 2 O where tptz is 2,4,6-tris(2-pyridyl)-1,3,5-triazine has been synthesized in ethanol solution and crystallized by diffusion of ether into ethanol solution of the complex and characterized by X-ray crystallography, spectroscopic methods and elemental analyses. The compound crystallizes in the monoclinic space group I2/a (0.33 mm× 0.25 mm× 0.20 mm) with lattice parameters: a = 14.160(3), b = 14.874(3), c = 24.806(8) Å, α = 90, β = 100.66(3), γ = 90°, V = 5134(2) Å 3 and Z = 4. The Co(II) central ion is in a slightly distorted octahedral coordination geometry formed by three nitrogen atoms of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) ligand, two oxygen atoms of coordinated water molecules and a chloride ion complete the coordination sphere of the Co(II) cation. The O-H…Cl, O-H…O and O-H…N hydrogen bonds, together with the above mentioned π-π stacking interactions stabilize the entire network comprising complex and non-coordinated water molecules. Intermolecular interactions were investigated by Hirshfeld surfaces. Electronic properties such as HOMO and LUMO energies were derived. The vibrational absorption bands were identified by infrared spectroscopy. A new ionic cobalt complex [Co(tptz) Cl(H 2 O) 2 ]Cl. 5.5 H 2 O where tptz is 2,4,6-tris(2-pyridyl)-1,3,5-triazine has been synthesized in ethanol solution. DFT study and intermolecular interactions were investigated by Hirshfeld surfaces.

Synthesis, Spectroscopic and X-Ray Structure Determination of a New Mononuclear Terbium (III) Complex from the Ligand N,N'-1,5-bis(pyridylmethylidene) Carbonohydrazone (H2L)

In the title compound, [Tb(H2L)2(H2O)3].3Cl.4(H2O).(C2H5OH), the Tb3+ is nine-coordinated in a distorted monocapped square antiprismgeometry by four nitrogen atoms, two oxygen atoms from the ligand molecules of the tridentate N,N'-1,5-bis(pyridylmethylidene) carbonohydrazone) (H2L) and three oxygen atoms of coordinating water molecules. The structure of the complex was elucidated by X-ray diffraction analysis. Suitable crystals were grown by slow evaporation of ethanol solution. The compound crystallizes in the triclinic crystal system with a space group of Pī. The asymmetric unit of the compound contains two neutral ligand molecules, oneterbium ion, three coordinated water molecules, five and half uncoordinated water molecules and one uncoordinated ethanol molecule. In the crystal, the complex cations are linked by hydrogen bonds into layers. These layers, chloride anions and non-coordinating water molecules are connected by O—H···O, O—H···N, O—H···Cl, N—H···O, N—H···Cl and C—H···Cl hydrogen bonds into a three-dimensional structure.

Solid-State Self-Assembly of a Linear Hexanuclear Copper(II) Oxamate Complex with Alternating Antiferro- and Ferromagnetic Coupling

In this work, we describe the synthesis, crystal structure and magnetic properties of the neutral hexacopper(II) complex of formula {[Cubpca)]2[Cu(dmopba)(H2O)]}2·4H2O (1), where Hbpca = bis(2-pyridylcarbonyl)-amide and dmopba = 4,5-dimethyl-1,2-phenylenebis(oxamato). Single crystals of 1 were obtained from the stoichiometric reaction (1:2 molar ratio) of the mononuclear copper(II) complexes (n-Bu4N)2[Cu(dmpba)] and [Cu(bpca)(H2O)2]NO3·2H2O through slow diffusion techniques in water as a solvent. The crystal structure of 1 shows that two neutral {[Cu(bpca)]2[Cu(dmopba)(H2O)]} trinuclear units are connected through double out-of-plane copper to outer carboxylate oxygen atoms resulting in a unique oxamate-bridged linear hexanuclear complex. Hydrogen bonds among adjacent entities involving the non-coordinated water molecules result in a supramolecular 3D network. Magnetic measurements on 1 show the occurrence of moderate antiferromagnetic intratrinuclear interactions between the copper(II) ions from the [Cu(bpca)]+ and [Cu(dmopba)(H2O)]2− fragments across the oxamate bridge and a weak intertrinuclear ferromagnetic interaction between the copper(II) ions that occurs between the two central [Cu(bpca)]+ fragments mediated by the carboxylate groups from the oxamate bridge [J = −31.96(2) cm−1 and J′ = +1.34(2) cm−1; H = J (S1·S2 + S2·S3 + S1′·S2′ + S2′·S3′) + J′ (S1·S1′)].

Crystal structures of two new divalent transition-metal salts of carb-oxy-benzene-sulfonate anions.

Hexa-aqua-nickel(II) bis-(3-carb-oxy-4-hy-droxy-benzene-sulfonate) dihydrate, [Ni(H2O)6][C6H3(CO2H)(OH)SO3]2·2H2O, (I), crystallizes in the triclinic space group P with the nickel(II) aqua complexes on centers of inversion. The carboxyl-ate group is protonated and neither it nor the sulfonate group is involved in direct coordination to the metal ions. The structure consists of alternating layers of inorganic cations and organic anions linked by O-H⋯O hydrogen bonds that also include non-coordinated water mol-ecules of crystallization. The first-row divalent transition-metal salts of this anion are reported as both dihydrates and tetra-hydrates, with two distinct structures for the dihydrates that are both layered but differ in the hydrogen-bonding pattern. Compound (I) represents the second known example of one of these structures. Hexa-aqua-cobalt(II) bis-(3-carb-oxy-benzene-sulfonate) dihydrate, [Co(H2O)6][C6H4(CO2H)SO3]2·2H2O, (II), also crystallizes in triclinic P with the cobalt(II) aqua complexes on centers of inversion. The structure is also built of alternating layers of complex cations and organic anions without direct coordination to the metal by the protonated carboxyl-ate or unprotonated sulfonate groups. A robust O-H⋯O hydrogen-bonding network involving primarily the coordin-ated and non-coordinated water mol-ecules and sulfonate groups directs the packing. This is the first reported example of a divalent transition-metal salt of the 3-carb-oxy-benzene-sulfonate anion.

Synthesis and crystal structure of bis-[trans-di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)nickel(II)] trans-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)bis-[4,4',4''-(1,3,5-tri-methyl-benzene-2,4,6-tri-yl)tris-(hydrogen phenyl-phospho-nato-κO)]nickel(II) deca-hydrate.

The components of the title compound, [Ni(C10H24N4)(H2O)2]2[Ni(C10H24N4)(C27H24O9P3)2]·10H2O are two centrosymmetric [Ni(C10H24N4)(H2O)2]2+ dications, a centrosymmetric [Ni(C10H24N4)(C27H24O9P3)2]4- tetra-anion and five crystallographically unique water mol-ecules of crystallization. All of the nickel ions are coordinated by the four secondary N atoms of the macrocyclic cyclam ligands, which adopt the most energetically stable trans-III conformation, and the mutually trans O atoms of either water mol-ecules in the cations or the phospho-nate groups in the anion in a tetra-gonally distorted NiN4O2 octa-hedral coordination geometry. Strong O-H⋯O hydrogen bonds between the protonated and the non-protonated phospho-nate O atoms of neighboring anions result in the formation of layers oriented parallel to the bc plane, which are linked into a three-dimensional network by virtue of numerous N-H⋯O and O-H⋯O hydrogen bonds arising from the sec-NH groups of the macrocycles, phospho-nate O atoms and coordinated and non-coordinated water mol-ecules.

FeIII in a high-spin state in bis(5-bromosalicylaldehyde 4-ethylthiosemicarbazonato-κ3O,N1,S)ferrate(III) nitrate monohydrate, the first example of such a cationic FeIII complex unit.

The synthesis and crystal structure (100 K) of the title compound, [Fe(C10H11BrN3OS)2]NO3·H2O, is reported. The asymmetric unit consists of an octahedral [FeIII(HL)2]+ cation, where HL- is H-5-Br-thsa-Et or 5-bromosalicylaldehyde 4-ethylthiosemicarbazonate(1-) {systematic name: 4-bromo-2-[(4-ethylthiosemicarbazidoidene)methyl]phenolate}, a nitrate anion and a noncoordinated water molecule. Each HL- ligand binds via the thione S, the imine N and the phenolate O atom, resulting in an FeIIIS2N2O2 chromophore. The ligands are orientated in two perpendicular planes, with the O and S atoms in cis and the N atoms in trans positions. This [Fe(HL)2](anion)·H2O compound contains the first known cationic FeIII entity containing two salicylaldehyde thiosemicarbazone derivatives. The FeIII ion is in the high-spin state at 100 K. In addition, a comparative IR spectroscopic study of the free ligand and the ferric complex is presented, demonstrating that such an analysis provides a quick identification of the degree of deprotonation and the coordination mode of the ligand in this class of metal compounds. The variable-temperature magnetic susceptibility measurements (5-320 K) are consistent with the presence of a high-spin FeIII ion with a zero-field splitting D= 0.439 (1) cm-1.

Synthesis, characterization and catalytic studies of chromium(III) porphyrin complex with axial cyanate ligands

We report the synthesis and the spectroscopic, structural and electrochemical characterization of a new chromium(III) coordination compound namely the bis(cyanato-κN)[meso-tetratolylporphyrinato]chromate(III) (cryptand-222)potassium dihydrate [K(crypt-222)][CrIII(TTP)(NCO)2]·2H2O (complex I). This compound crystallizes in the orthorhombic crystal system with the non-centrosymmetric space group C2221. The chromium and the potassium atoms are located at special positions in a two-fold axis. The crystal lattice of complex I is stabilized by O__H…O, C__H…O, C__H…N and C__H…π intermolecular contacts involving the negatively charged [CrIII(TTP)(NCO)2]− species, the [K(crypt-222)]+ counterions and the two non-coordinated water molecules. Further insights on these weak intermolecular contacts are provided by the Hirshfeld surface analysis. Molecular electrostatic potential (MEP) theoretical calculation on [K(crypt-222)][CrIII(TTP)(NCO)2]·2H2O are reported. The new Cr(III) complex was efficient as a catalyst in the decomposition of the Rhodamine B (RbH) dye by hydrogen peroxide. This coordination compound was also tested as a photocatalyst of the photodecomposition of the RbH dye by molecular oxygen.

Crystal structures of catena-poly[[μ-aqua-di-aqua(μ3-2-methyl-propano-ato-κ4 O:O,O':O')calcium] 2-methyl-propano-ate dihydrate], catena-poly[[μ-aqua-di-aqua-(μ3-2-methyl-propano-ato-κ4 O:O,O':O')strontium] 2-methyl-propano-ate dihydrate] and catena-poly[[μ-aqua-di-aqua-(μ3-2-methyl-propano-ato-κ4 O:O,O':O')(calcium/strontium)] 2-methyl-propano-ate dihydrate

The crystal structures of catena-poly[[μ-aqua-di-aqua-(μ3-2-methyl-propano-ato-κ4 O:O,O':O')calcium] 2-methyl-propano-ate dihydrate], {[Ca(C4H7O2)(H2O)3](C4H7O2)·2H2O} n , (I), catena-poly[[μ-aqua-di-aqua-(μ3-2-methyl-propano-ato-κ4 O:O,O':O')strontium] 2-methyl-propano-ate dihydrate], {[Sr(C4H7O2)(H2O)3](C4H7O2)·2H2O} n , (II), and catena-poly[[μ-aqua-di-aqua-(μ3-2-methyl-propano-ato-κ4 O:O,O':O')(calcium/strontium)] 2-methyl-propano-ate dihydrate], {[(Ca,Sr)(C4H7O2)(H2O)3](C4H7O2)·2H2O} n , (III), are related. (III) can be considered as an Sr-containing solid solution of (I), with Ca2+ and Sr2+ occupationally disordered in the ratio 0.7936 (16):0.2064 (16). (I)/(III) and (II) are homeotypic with different space groups of Pbca and Cmce, respectively. All the title crystal structures are composed of hydro-philic sheets containing the cations, carboxyl-ate groups as well as water mol-ecules. The hydro-phobic layers, which consist of 2-methyl-propano-ate chains, surround the hydro-philic sheets from both sides, thus forming a sandwich-like structure extending parallel to (001). The cohesion forces within these sheets are the cation-oxygen bonds and O-H⋯O hydrogen bonds of moderate strength. Stacking of these sandwiches along [001] is consolidated by van der Waals forces. The structures contain columns defined by the cation-oxygen inter-actions in which just one symmetry-independent 2-methyl-propano-ate anion is included, together with three water mol-ecules. These mol-ecules participate in an irregular coordination polyhedron composed of eight O atoms around the cation. Additional water mol-ecules as well as the second 2-methyl-propano-ate anion are not part of the coordination sphere. These mol-ecules are connected to the above-mentioned columns by O-H⋯O hydrogen bonds of moderate strength. In (II), the Sr2+ cation, two of the coordinating water mol-ecules and both anions are situated on a mirror plane with a concomitant positional disorder of the 2-methyl-propyl groups; the non-coordinating water mol-ecule also shows positional disorder of its hydrogen atom.

Proton Conduction in a Single Crystal of a Phosphonato-Sulfonate-Based Coordination Polymer: Mechanistic Insight.

The proton conduction properties of a phosphonato‐sulfonate‐based coordination polymer are studied by impedance spectroscopy using a single crystal specimen. Two distinct conduction mechanisms are identified. Water‐mediated conductance along the crystal surface occurs by mass transport, as evidenced by a high activation energy (0.54 eV). In addition, intrinsic conduction by proton ′hopping′ through the interior of the crystal with a low activation energy (0.31 eV) is observed. This latter conduction is anisotropic with respect to the crystal structure and seems to occur through a channel along the c axis of the orthorhombic crystal. Proton conduction is assumed to be mediated by sulfonate groups and non‐coordinating water molecules that are part of the crystal structure.

A new hydrate of magnesium carbonate, MgCO3·6H2O.

During investigations of the formation of hydrated magnesium carbonates, a sample of the previously unknown magnesium carbonate hexahydrate (MgCO3·6H2O) was synthesized in an aqueous solution at 273.15 K. The crystal structure consists of edge-linked isolated pairs of Mg(CO3)(H2O)4 octahedra and noncoordinating water molecules, and exhibits similarities to NiCO3·5.5H2O (hellyerite). The recorded X-ray diffraction pattern and the Raman spectra confirmed the formation of a new phase and its transformation to magnesium carbonate trihydrate (MgCO3·3H2O) at room temperature.

Investigation of electrical conductance properties, non-covalent interactions and TDDFT calculation of a newly synthesized copper(II) metal complex

[Cu(pydc)(apy)]·3H2O (1) (pydcH2 = pyridine-2,6-dicarboxylic acid; apy = 2- aminopyridine) has been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction techniques. Crystallographic analysis tells that the complex 1 has distorted square pyramid geometry with pydcH2 coordinated as a tridentate ligand to each metal ion through two oxygen atoms of each carboxylate group and the nitrogen atom of the pyridine moiety. Three non-coordinated water molecules are present in the asymmetric unit and all are involved in constructing a (H2O)6 cluster with chair conformation like cyclohexane. Interestingly, The average O⋯O distance of 2.759 Å in water hexamer of Complex 1 is closer to the respective distance of ice (2.76 Å for ice Ih at 90 K) than to that of bulk liquid water (2.85 Å). Also, the average O–O–O bond angle of 107.96° is close to the tetrahedral angle in ice Ih form. Apart from water cluster, the aromatic molecules are engaged in several non-covalent interactions like NH … π, lone pair … π, π … π and hydrogen bonds. These types of non-covalent interactions attribute to the supramolecular framework of the studied molecule. The electrical conductivity in terms of current was measured at room temperature before and after annealed of the synthesized complex compound on thin film specimen of order 230 and 240 μA respectively with bias voltage 1 V. In addition, the electronic transitions of 1 were recorded and the electronic distribution of HOMO-LUMO was rationalized theoretically (through time-dependent density functional theory (TDDFT)).

Crystal structures of two coordination isomers of copper(II) 4-sulfo-benzoic acid hexa-hydrate and two mixed silver/potassium 4-sulfo-benzoic acid salts.

A reaction of copper(II) carbonate and potassium 4-sulfo-benzoic acid in water acidified with hydro-chloric acid yielded two crystalline products. Tetra-aqua-bis-(4-carb-oxy-benzene-sulfonato)-copper(II) dihydrate, [Cu(O3SC6H4CO2H)2(H2O)4]·2H2O, (I), crystallizes in the triclinic space group P with the Cu2+ ions located on centers of inversion. Each copper ion is coordinated to four water mol-ecules in a square plane with two sulfonate O atoms in the apical positions of a Jahn-Teller-distorted octa-hedron. The carboxyl-ate group is protonated and not involved in coordination to the metal ions. The complexes pack so as to create a layered structure with alternating inorganic and organic domains. The packing is reinforced by several O-H⋯O hydrogen bonds involving coordinated and non-coordinated water mol-ecules, the carb-oxy-lic acid group and the sulfonate group. Hexa-aqua-copper(II) 4-carb-oxy-benzene-sulfonate, [Cu(H2O)6](O3SC6H4CO2H)2, (II), also crystallizes in the triclinic space group P with Jahn-Teller-distorted octa-hedral copper(II) aqua complexes on the centers of inversion. As in (I), the carboxyl-ate group on the anion is protonated and the structure consists of alternating layers of inorganic cations and organic anions linked by O-H⋯O hydrogen bonds. A reaction of silver nitrate and potassium 4-sulfo-benzoic acid in water also resulted in two distinct products that have been structurally characterized. An anhydrous silver potassium 4-carb-oxy-benzene-sulfonate salt, [Ag0.69K0.31](O3SC6H4CO2H), (III), crystallizes in the monoclinic space group C2/c. There are two independent metal sites, one fully occupied by silver ions and the other showing a 62% K+/38% Ag+ (fixed) ratio, refined in two slightly different positions. The coordination environments of the metal ions are composed primarily of sulfonate O atoms, with some participation by the non-protonated carboxyl-ate O atoms in the disordered site. As in the copper compounds, the cations and anions cleanly segregate into alternating layers. A hydrated mixed silver potassium 4-carb-oxy-benzene-sulfonate salt dihydrate, [Ag0.20K0.80](O3SC6H4CO2H)·2H2O, (IV), crystallizes in the monoclinic space group P21/c with the Ag+ and K+ ions sharing one unique metal site coordinated by two water mol-ecules and six sulfonate O atoms. The packing in (IV) follows the dominant motif of alternating inorganic and organic layers. The protonated carboxyl-ate groups do not inter-act with the cations directly, but do participate in hydrogen bonds with the coordinated water mol-ecules. (IV) is isostructural with pure potassium 4-sulfo-benzoic acid dihydrate.