Syntheses, structures and magnetic properties of Mn(II), Co(II) and Ni(II) metal-organic frameworks constructed from 1,3,5-benzenetricarboxylate and formate ligands

Three compounds, [(CH₃)₂NH₂][M₃(BTC)(HCOO)₄(H₂O)]·H₂O (M = Mn (1), Co (2), Ni (3), H₃BTC = 1,3,5-benzenetricarboxylic acid), were synthesized under hydrothermal conditions and were characterized by single crystal and powder X-ray diffraction, IR spectra, elemental analysis, coupled TG-MS and magnetic measurements. Compounds 1-3 are isostructural analogues and crystallize in monoclinic space group P2₁/c. Each metal ion in these compounds connects to six oxygen atoms to form a MO₆ octahedron. Six MO₆ octahedra link to each other to form a corner-shared hexameric M₆ cluster, which is linked by BTC ligands to form two-dimensional layers. The two-dimensional layers are further connected by formic ions to form a three-dimensional network with channels, where (CH₃)₂NH₂⁺ ions and water molecular are located. Magnetic measurements indicate that anti-ferromagnetic ordering occurs at low temperature for these compounds.     

Preparation, crystal structure and luminescent properties of the 3-D netlike supramolecular lanthanide picrate complexes with 2,2′-[1,2-phenylenebis(oxy)]bis(N-benzylacetamide)

Solid complexes of lanthanide picrates with a new podand-type ligand, 2,2′-[(1,2-phenylene)bis(oxy)]bis(N-benzylacetamide) (L) have been prepared and characterized by elemental analysis, conductivity measurements, IR, electronic and ¹H NMR spectroscopies. The crystal and molecular structures of the complex NdL(Pic)₃ have been determined by single-crystal X-ray diffraction. The crystal structure shows that the Nd(III) ion is coordinated with four oxygen atoms of the ligand L and six oxygen atoms of three bidentate picrates. Furthermore, the NdL(Pic)₃ complex units are linked by the intermolecular hydrogen bonds to form a three-dimensional (3-D) netlike supermolecule. Under excitation, Eu complex exhibited characteristic emissions. The lowest triplet state energy level of the ligand indicates that the triplet state energy level of the ligand matches better to the resonance level of Eu(III) than Tb(III) ion.     

Synthesis and characterization of new dinuclear complexes of molybdenum(V) with β′-hydroxy-β-enaminones

New dinuclear molybdenum(V) complexes have been obtained by the reaction of [Mo₂O₃(acac)₄] (acac=acetilacetonate ion) with the polydentate ligands, β′-hydroxy-β-enaminones. All prepared complexes consist of Mo₂O₄ ²⁺ core coordinated by two ligands as in the β-diketonates only through two donor oxygen atoms. Such bonding gives the opportunity for the sixth coordination place around molybdenum to be completed by the monodentate solvent molecule D. All compounds have been characterized by means of elemental analyses, one- and two-dimensional NMR spectroscopy, IR spectroscopy as well as by thermal analyses. The molecular and crystal structures of the molybdenum(V) complexes 1a and 1b coordinated by two different isomeric ligands as well as of the isomer a itself have been determined by a single crystal X-ray diffraction method.     

Hydrothermal syntheses, structural characterizations and magnetic properties of cobalt(II) and manganese(II) coordination polymeric complexes containing pyrazinecarboxylate ligand

Two novel coordination polymeric complexes [Co(pzca)₂(H₂O)]_n (1) and [Mn(pzca)₂]_n (2) (pzca=2-pyrazinecarboxylate) have been synthesized by hydrothermal reaction of M(CH₃COO)₂·4H₂O (M=Co, Mn) and 2-pyrazinecarboxylic acid. The complex 1 displays an infinite zigzag chain structure in which each cobalt(II) center was coordinated by three nitrogen and three oxygen atoms to generate a CoN₃O₃ octahedral geometry. The existence of hydrogen bond leads to the formation of the interpenetrating stacking structure. Complex 2 indicates a two-dimensional layer structure through the linkage of bridging oxygen atom of pzca ligand. Each Mn(II) center exhibits a distorted octahedral coordination environment with four oxygen atoms and two nitrogen atoms. The distances of adjacent Mn(II) atoms are 3.503 and 5.654 Å, respectively. The magnetic property analyses reveal that both complexes show weak antiferromagnetic exchange interactions between the metal centers.     

<Emphasis Type="Italic">Ab initio</Emphasis> calculations of ionic hydrocarbon compounds with heptacoordinate carbon

Ionic hydrocarbon compounds that contain hypercarbon atoms, which bond to five or more atoms, are important intermediates in chemical synthesis and may also find applications in hydrogen storage. Extensive investigations have identified hydrocarbon compounds that contain a five- or six-coordinated hypercarbon atom, such as the pentagonal-pyramidal hexamethylbenzene, C₆(CH₃)₆²⁺, in which a hexacoordinate carbon atom is involved. It remains challenging to search for further higher-coordinated carbon in ionic hydrocarbon compounds, such as seven- and eight-coordinated carbon. Here, we report ab initio density functional calculations that show a stable 3D hexagonal-pyramidal configuration of tropylium trication, (C₇H₇)³⁺, in which a heptacoordinate carbon atom is involved. We show that this tropylium trication is stable against deprotonation, dissociation, and structural deformation. In contrast, the pyramidal configurations of ionic C₈H₈ compounds, which would contain an octacoordinate carbon atom, are unstable. These results provide insights for developing new molecular structures containing hypercarbon atoms, which may have potential applications in chemical synthesis and in hydrogen storage.

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Graphical abstract Possible structural transformations of stable configurations of (C₇H₇)³⁺, which may result in the formation of the pyramidal structure that involves a heptacoordinate hypercarbon atom.

     

Polyoxometalate cluster [V12B18O60H6] functionalized with the copper(II) bis-ethylenediamine complex

Three compounds based on the polyoxometalate building block [V₁₂B₁₈O₆₀H₆], (Na)₁₀[(H₂O)V₁₂B₁₈O₆₀H₆]·18H₂O (1), Na₈[Cu(en)₂]₂[V₁₂B₁₈O₆₀H₆](NO₃)₂·14.7H₂O (2), Na₇[Cu(en)₂]₂[V₁₂B₁₈O₆₀H₆](NO₃)·15.5H₂O (3), (en = ethylenediamine), have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analysis and TGA. Compound 1 consists of polyoxovanadium borate [V₁₂B₁₈O₆₀H₆] clusters which are surrounded by sodium countercations in octahedral sites, stabilized by electrostatic interactions with the oxygen atoms of both vanadium and boron centres. However, compounds 2 and 3 correspond to more complicated structures, constructed from the same polyoxometalate clusters, which are interconnected by [Cu(en)₂]²⁺ moieties via the terminal oxygen atoms of the polyoxoanions, generating one-dimensional structures. The functionalization of this polyoxovanadium borate cluster has been obtained by the use of [Cu(en)₂]²⁺ complex ions, thus demonstrating the capacity of the terminal oxygen atoms of the cluster to bind transition metal centres. The structural stability of the [V₁₂B₁₈O₆₀H₆] cluster permits the formation of functionalized polyoxometalate clusters, generating various crystalline lattices.     

Dihydroxyacetone phosphate, DHAP, in the crystalline state: monomeric and dimeric forms

It was shown that dihydroxyacetone phosphate may exist in both monomeric DHAP (C₃H₇O₆P) and dimeric DHAP-dimer (C₆H₁₄O₁₂P₂) form. Monomeric DHAP was obtained in the form of four crystalline salts: CaCl(DHAP)·2.9H₂O (7a), Ca₂Cl₃(DHAP)·5H₂O (7b), CaCl(DHAP)·2H₂O (7c), and CaBr(DHAP)·5H₂O (7d) by crystallization from aqueous solutions containing DHAP acid and CaCl₂ or CaBr₂, or by direct crystallization from a solution containing DHAP precursor and CaCl₂. At least one of the salts is stable and may be stored in the crystalline state at room temperature for several months. The dimeric form was obtained by slow saturation of free DHAP syrup with ammonia at −18 °C and isolated in the form of its hydrated diammonium salt (NH₄)₂(DHAP-dimer)·4H₂O (8). The synthesis of the compounds, their crystallization, and crystal structures determined by X-ray crystallography are described. In all 7a-d monomeric DHAP exists in the monoanionic form in an extended (in-plane) cisoid conformation, with both hydroxyl and ester oxygen atoms being synperiplanar to the carbonyl O atom. The crucial structural feature is the coordination manner, in which the terminal phosphate oxygen atoms act as chelating as well as bridging atoms for the calcium cations. Additionally, the DHAP monoanions chelate another Ca²⁺ by the α-hydroxycarbonyl moiety, in a manner observed previously in dihydroxyacetone (DHA) calcium chloride complexes. In dimeric 8 the anion is a trans isomer with the dioxane ring in a chair conformation with the hydroxyl groups in axial positions and the phosphomethyl group in an equatorial position.     

Syntheses, structures and luminescence of Europium α-thiophene carboxylates coordination polymer and supramolecular compound

Two europium α-thiophene carboxylic acid (HTPA) compounds, coordination polymer Eu(TPA)₃(HTPA)₂ (1) (TPA=α-thiophene carboxylate) and supramolecular compound Eu(TPA)₃(H₂O)₃ · 0.5H₂O (2) with luminescence and triboluminescence, have been synthesized and structurally characterized. In 1 each europium is bridged by six oxygen atoms from six carboxylates and coordinated with two carboxyl oxygen atoms from two α-thiophene carboxylic acid molecules, resulting in a coordination number of eight to Eu. For 2 each europium is chelated by six oxygen atoms from six carboxylates and coordinated with three oxygen atoms from three coordinated water generating a coordination number nine to Eu; A supramolecular compound is constructed through hydrogen bonds. Both 1 and 2 display strong characteristic emission of Eu³⁺ ion radiated by UV light and produce twinkling red light with an external force.     

One-dimensional helical coordination polymers of cobalt(II) and iron(II) ions with 2,2′-bipyridyl-3,3′-dicarboxylate (BPDC)

One-dimensional (1-D) helical coordination polymers, [M^II(H₂O)₃(BPDC)]_n · nH₂O (M = Co (1), Fe (2)), have been prepared by the self-assembly of cobalt(II) and iron(II) ions, respectively, with 2,2′-bipyridyl-3,3′-dicarboxylic acid (H₂BPDC) in an aqueous solution. X-ray crystal structures of compounds 1 and 2 show that each metal ion displays a distorted octahedral coordination geometry including three water oxygen atoms, one oxygen atom of the carboxylate of a BPDC²⁻ belonging to the adjacent metal ion and two nitrogen atoms from the BPDC²⁻ acting as a chelating ligand. In 1 and 2, one carboxylate oxygen atom of coordinated BPDC²⁻ binds to the neighboring metal ion, which give rise to 1-D helical coordination polymers. The helical chains of 1 and 2 are linked by the hydrogen bonding interactions between the carboxylate oxygen atom of the BPDC²⁻ ion belonging to a chain and the water molecule of the adjacent helical chain, which lead to 2-D networks extending along the ab plane. The supramolecules 1 and 2 show isomorphous structures regardless of the metal ions.     

Lanthanide complexes with disulfide ligand generated in situ: Syntheses, crystal structures and fluorescent properties

Five new lanthanide complexes [Ln₂(DTDN)₄(phen)₄]·7H₂O·2H₃O⁺ (Ln = Nd (1), Sm (2), Eu (3), Tb (4), Dy (5), H₂DTDN = 2,2′-dithiodinicotinic acid, phen = 1,10-phenanthroline) have been solvothermally synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, IR spectra, and TG analyses. By in situ oxidation of 2-mercaptonanicotinic acid (2-H₂MN), the expected ligand H₂DTDN was generated. All crystals are isostructural and crystallize in monoclinic system with space group C2/c. The metal center is eight-coordinated completely by four carboxylic oxygen atoms from four different DTDN²⁻ ligands, and four nitrogen atoms from two phen molecules with a distorted square-antiprismatic geometry. The structures can be considered as two-dimensional (2D) structures and further linked by hydrogen bonds into the final trinodal 4-connected network. Photoluminescence studies revealed that complexes 2-5 exhibit strong fluorescent emission bands in the solid state at room temperature.     

Preparation, characterisation and crystal structure of two zinc(II) benzoate complexes with pyridine-based ligands nicotinamide and methyl-3-pyridylcarbamate

Two benzoate complexes namely tetrakis(μ₂-benzoato-O,O^′)-bis(μ₂-benzoato-O,O)-bis(nicotinamide-N)-tri-zinc(II), [Zn₃(benz)₆(nia)₂] (I) and bis(benzoato-O)-bis(methyl-3-pyridylcarbamate-N)-zinc(II), [Zn(benz)₂(mpcm)₂] (II) (benz=benzoate anion, nia=nicotinamide, mpcm=methyl-3-pyridylcarbamate) were prepared and characterised by elemental analysis, IR spectroscopy, thermal analysis and X-ray structure determination. The structure of the complex I is centrosymmetric, formed by a linear array of three zinc atoms. The central zinc atom shows octahedral coordination and is bridged to each of the terminal zinc atoms by three benzoate anions. Two of them act as bidentate, one as monodentate ligand. By additional coordination of the nia ligand, the terminal Zn atoms adopt tetrahedral surrounding. The structure of complex II contains two crystallographically independent [Zn(benz)₂(mpcm)₂] molecules. In each molecule, the zinc atom is tetrahedrally coordinated by two monodentate benzoate and two methyl-3-pyridylcarbamate ligands. Intermolecular hydrogen bonds of the N-H?O type connect molecules in the structures of complexes I and II to form a two-dimensional network. The three different types of carboxylate binding found in the complexes were distinguished also by values of carboxylate stretching vibrations in FT-IR spectra as well as by thermal decomposition of the complexes in nitrogen.     

Two novel sandwiched-type polyoxotungstates containing Zn6 transition-metal cluster: Syntheses, structures and luminescent property

Two novel Zn6 sandwiched polyoxometalates, [Zn(phen)₂]₂[Zn₆(phen)₂(AsW₉O₃₃)₂] (1) and K₁₁H₂Zn[(ZnCl)₆(AsW₉O₃₃)₂]Cl · 27H₂O (2), have been synthesized and characterized by X-ray single-crystal analysis, IR, and fluorescence spectrum. The polyoxoanions in both compounds can be characterized as two {As^IIIW₉O₃₃}⁹⁻ moieties linked through Zn6 transition-metal cluster to form the sandwich-type polyoxotungstates. In compound 1, six Zn atoms in the equatorial part of the polyoxoanions have two different coordination environments: four Zn sites exhibit distorted octahedral geometry, and the other two Zn atoms show square pyramidal geometry. In the polyoxoanion of compound 2, all Zn atoms are square pyramidal geometry, and held together to form a hexagonal metallocycle by edge-sharing oxygen atoms. In this Zn6 cluster, the shortest distance of neighboring Zn?Zn is 3.147(1) Å. In addition, compound 2 exhibits purple photoluminescence at room temperature.     

First examples of ternary lanthanide 2,2′-bipyridine-3,3′-dicarboxylate coordination polymers with zigzag chains structures assembled from lanthanide ions, 2,2′-bipyridine-3,3′-dicarboxylate and 1,10-phenanthroline

Four lanthanide coordination polymers, [{Ln₂(bpdc)₃(phen)₂(H₂O)₂} · (H₂O)₆]_n (Ln = Sm (1); Eu (2); Gd (3), Tb (4)), were self-assembled from 2,2′-bipyridine-3,3′-dicarboxylic acid (H₂bpdc),1,10-phenanthroline(phen) and corresponding lanthanide oxides by hydrothermal synthesis. Compounds 1-4 are found to be isomorphous and isostructural. Single-crystal X-ray diffraction studies show that compounds 1-4 are all of one-dimensional zigzag chain structures and extend to two-dimensional networks through π-π interactions and hydrogen bonds. The pyridyl nitrogen atoms of the 2,2′-bipyridyl unit in the bpdc ligand are uncoordinated in an anti-conformation along the central C-C bond of the ligand. Thermogravimetric analysis of 1-4 showed an obvious thermal stability indicating that the coordination habit of the metal ions with bpdc and phen has an effect on the overall framework. Photoluminescence measurement indicates that compound 2 and compound 4 are strong red and green emitters, respectively.     

Mono- and dinuclear Fe(III) complexes with the N2O2 donor 5-chlorosalicylideneimine ligands; synthesis, X-ray structural characterization and magnetic properties

Two novel monomeric [C₁₈H₁₇Cl₃N₂O₂Fe] (1) and dimeric [C₃₈H₃₆N₄O₄Cl₆Fe₂] (2) Fe(III) tetradentate Schiff base complexes have been synthesized and their crystal structures have been determined by single crystal X-ray diffraction analysis. In complex (1) the Schiff base ligand coordinates toward one iron atom in a tetradentate mode and each iron atom is five coordinated with the coordination geometry around iron atom which can be described as a distorted square pyramid. The presence of a short (2.89 Å) non-bonding interatomic Fe···O distances between adjacent monomeric Fe(III) complexes results in the formation of a dimer. Structural analysis of compound (2) shows that the structure is a centrosymmetric dimer in which the six coordinated Fe(III) atoms are linked by μ-phenoxo bridges from one of the phenolic oxygen atoms of each Schiff base ligand to the opposite metal center. The variable-temperature (2-300 K) magnetic susceptibility (χ) data of these two compounds have been investigated. The results show that for both complexes Fe(III) centers are in the high spin configuration (S = 5/2) and indicate antiferromagnetic spin-exchange interaction between Fe(III) ions. The obtained results are briefly discussed using magnetostructural correlations developed for other class of iron(III) complexes.     

A tridentate bis(pyrazolyl) ligand binds to Cu(II), without using the pyrazole group: a very unusual coordination mode of the ligand Hbdmpb, 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-butanoic acid

A new pyrazole-based ligand, namely 1,3-bis(3,5-dimethylpyrazol-1-yl)-2-butanoic acid (Hbdmpb) was synthesised together with its copper complex Na[Cu(bdmpb)₂(OOCCH₃)H₂O] · 4H₂O. Both the free ligand and its Cu compound were fully characterised and their crystal structures were determined by X-ray analysis. The free-ligand molecular structure is uneventful. The Cu compound is highly unusual, as the pyrazole nitrogen atoms do not bind to the Cu ion. The copper(II) ion is coordinated by four nearly coplanar oxygen atoms from two dehydronated ligands bdmpb (CuO(1a) 1.942(4), CuO(1b) 1.933(4) Å), a monodentate acetate group (CuO(1) 1.927(3) Å) and a water molecule (CuO(1w) 1.937(4) Å). The nitrogen atoms of the pyrazole rings do not coordinate to the metal center, but instead are involved in strong intramolecular hydrogen bonds. The coordinated water molecule is strongly H-bonded to two pyrazole N atoms from two bdmpb ligands (N(12a) ? HO(1w) 2.762(7), N(12b) ? HO(1w) 2.774(7) Å). The other two pyrazole N atoms with a lone pair are hydrogen-bonded to water molecules in the lattice (N(22a) ? HO(2w) 2.763(7), N(22b) ? HO(6w) 2.892(7) Å). The sodium ion is six-coordinated by the oxygen atom O(2) of the acetato ligand and by five water molecules. The EPR spectrum recorded in the solid state shows a characteristic signal for an axial anisotropic S = 1/2 species. The spectrum recorded in methanol glass confirms the absence of the coordination of pyrazole nitrogen atoms to the copper centers.     

Synthesis, crystal structure and photoluminescent properties of an aromatic bridged Schiff base ligand and its zinc complex

An aromatic bridged Schiff base ligand, N,n′-bis((4,4′-diethylamino)salicylidene)-1,2-phenylenediamine (H₂L³), and its trinuclear Zinc(II) complex, , were synthesized and characterized by means of elemental analyses, FT-IR and UV-Vis absorption spectra, and single crystal X-ray crystallography. The X-ray crystal structure of the complex reveals that the zinc ion (Zn1 or Zn1A) is coordinated by two oxygen atoms in phenolate and two nitrogen atoms in imines of the ligand and one oxygen atom of the acetate, the zinc ion (Zn2) is coordinated by four oxygen atoms in phenolate of the ligands and two oxygen atoms of the acetates. Two acetates coordinate to three zinc ions through Zn-O-C-O-Zn bridges. The complex exhibits blue-green emission as the result of the fluorescence from the intraligand emission excited state. In addition, the ground-state geometries, the lowest energy transition and the UV-Vis spectrum of the ligand have been studied with density functional theory (DFT) and time-dependent density functional theory (TD-DFT) at B3LYP/6-31G(d) level, showing that the calculation outcomes are in good agreement with experimental data.     

Synthesis, X-ray crystal structure and properties of a novel tetranuclear unsymmetrical (μ-SO4) copper(II) complex: relevance to SO2 fixation

The synthesis, by fixation of SO₂, the unusual crystal structure, and the spectral and redox properties of the new compound [Cu₄(TPPNOL)₂(μ-SO₄)₂](ClO₄)₂ (1) [HTPPNOL (N,N,N′-tris-(2-pyridylmethyl)-1,3-diaminopropan-2-ol)] are reported. In 1, the copper(II) ions are bridged by the alkoxo oxygen atoms of the HTPPNOL ligand and by exogenous sulfate bridges. The structure of 1 consists of a centro-symmetric tetranuclear core or a “Dimer of Dimers” complex, in which a μ-O,O′ sulfate oxygen atom is further coordinated to the copper centre of another similar dinuclear unit through a μ-O,O, sulfate bridge resulting in a tetranuclear arrangement. Thus, the dinuclear units are linked by two μ-O,O sulfate bridges. The simultaneous presence of two distinct coordination modes for the sulfate group in this structure is rare and 1 represents the first coordination compound presenting μ-O,O′ and μ-O,O type structures. The SO₂ fixation was monitored by changes in the electronic spectra which indicated the formation of the intermediate hydroxo complex [Cu₂(TPPNOL)(OH)₂]⁺, in basic medium, which, we propose, acts as the nucleophile in the SO₂ fixation mechanism.     

BODIPY for photodynamic therapy applications: computational study of the effect of bromine substitution on <Superscript>1</Superscript>O<Subscript>2</Subscript> photosensitization

Density functional theory and its time-dependent extension (DFT, TDDFT) were employed to establish the feasibility of using a series of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs) in photodynamic therapy. Their absorption electronic spectra, singlet–triplet energy gaps, and spin–orbit matrix elements were computed and are discussed here. The effects of bromine substitution on the photophysical properties of BODIPY were elucidated. The investigated compounds were found to possess different excited triplet states that lie below the energy of the bright excited singlet state (S₁ or S₂), depending on the positions occupied by the bromine atoms. The computed spin–orbit matrix elements for the radiationless intersystem crossing S_n?→ ?T_m and the relative singlet–triplet energy gaps allowed the prediction of plausible nonradiative decay pathways for the production of singlet excited molecular oxygen, the key cytotoxic agent in photodynamic therapy.

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Graphical Abstract The photophysical properties affected by the presence of bromine atoms in different positions of a BODIPY core have been here elucidated. In particular it has been found that SOC values strongly depend on the position of heavy atoms into the BODIPY core, suggesting positions 1 and 7 as the best ones to enhance the ISC kinetics

     

A molecular dynamics simulation of crystalline α-cyclodextrin hexahydrate

The structure of crystalline -cyclodextrin (-CD) hexahydrate, form I (C₃₆H₆₀O₃₀·6H₂O, space group P2₁2₁2₁) is experimentally so well determined by X-ray and by neutron diffraction analyses that the positions of all the hydrogen atoms are available. This provides an opportunity for testing an empirical force field that is currently used in simulations of protein and nucleic acid structures by performing molecular dynamics studies employing the GROMOS program package on a system of 4 unit cells containing 16 -CD molecules and 96 water molecules.A detailed comparison of the simulated and experimentally determined crystal structures shows that the experimental positions of the -CD atoms are reproduced within 0.025 nm, well within the overall experimental accuracy of 0.036 nm; that the water molecules are on average within 0.072 nm from their experimental sites, with two thirds reproduced within experimental accuracy by the calculations; that high correlation is produced, between the occurrence of simulated and experimentally observed hydrogen bonds.The good agreement between simulated and experimental results suggests that the tested force field is reliable.