A one-dimensional barium(II) coordination polymer with a coordinated nitro group of 2-nitrobenzoate

The aqueous reaction of barium carbonate with 2-nitrobenzoic acid (2-nbaH) results in the formation of a one-dimensional coordination polymer, catena-poly[[hexa(aqua)dibarium(II)]bis[(μ ₂-2-nitrobenzoate-O,O,O-NO₂)(μ ₂-2-nitrobenzoate-O,O,O′)]] 1. On heating at 100°C compound 1 is dehydrated to anhydrous barium bis(2-nitrobenzoate) 2. The anhydrous compound can be re-hydrated to 1 on exposure to water vapour. Compounds 1 and 2 were characterized by elemental analysis, IR and UV-Vis spectra, DSC thermograms, weight loss studies and the structure of 1 was determined. 1 and 2 can be thermally decomposed to BaCO₃ by heating at 800°C. The polymer [[Ba(H₂O)₃]₂(μ ₂-2-nba-O,O,O-NO₂)₂ (μ ₂-2-nba-O,O,O′)₂] _n 1 crystallizes in the centrosymmetric triclinic space group Pī and all atoms are located in general positions. The polymeric structure is based on a dimeric unit and consists of three water molecules coordinated to a central Ba(II) and two unique 2-nitrobenzoate (2-nba) anions, one of which (μ ₂-2-nba-O,O,O-NO₂) functions as a tridentate ligand and is linked to a Ba(II) through the oxygen atom of the-NO₂ group and forms a monoatomic μ ₂-carboxylate bridge between two symmetry related Ba(II) ions with a Ba···Ba distance of 4·5726(14) ?. The second unique 2-nba anion (μ ₂-2-nba-O,O,O′) also functions as a tridentate ligand with the carboxylate oxygen atoms linked to a Ba(II) ion in a bidentate fashion and one of the carboxylate oxygen atoms forming a monoatomic bridge between two symmetry related Ba(II) ions resulting in a Ba···Ba separation of 4·5406(15) ?. These differing tridentate 2-nba ligands link {Ba(H₂O)₃} units into a one-dimensional polymeric chain extending along b axis. In the infinite chain each nine coordinated Ba(II) is bonded to three water molecules and further linked to six oxygen atoms of four different 2-nitrobenzoate anions with alternating pairs of Ba(II) ions in the chain bridged by a pair of (μ ₂-2-nba-O,O,O-NO₂) and (μ ₂-2-nba-O,O,O′) ligands resulting in alternating Ba···Ba distances of 4·5406(15) and 4·5726(14) ? across the chain. Dedicated to Prof. S. K. Paknikar on the occasion of his 73rd birthday.     

Synthesis and structural characterization of a barium coordination polymer based on a μ2-monoatomic bridging 4-nitrobenzoate

Abstract

The synthesis, spectral characterization, crystal structure and properties of [Ba(H₂O)₂(NMF)₂(4-nba)₂], 1 (NMF = N-methylformamide; 4-nba = 4-nitrobenzoate), are reported. ¹H and ¹³C NMR spectral data reveal the presence of NMF in 1. A strong band at 1660?cm^?1 in the infrared spectrum indicates the binding of amide oxygen to Ba(II) which is confirmed by the single crystal structure. The unique Ba(II) in 1 situated on a mirror plane exhibits nine coordination and is bonded to two symmetry related monodentate terminal NMF ligands via the amide oxygen, and a terminal aqua ligand. The μ₂-monoatomic bridging binding mode of each of a crystallographically independent 4-nba ligand and a unique water ligand link the Ba(II) cations into an infinite chain extending along a, leading to the formation of a 1D coordination polymer with Ba···Ba separations of 4.2522(3) Å. In the chain, the {BaO₉} polyhedra are linked in a face sharing fashion. Thermal decomposition of 1 results in the formation of BaCO₃ residue. A comparative study of the structural chemistry of several barium coordination polymers is described.     

Solid state synthesis and characterization of a triple chain calcium(II) coordination polymer showing two different bridging 4-nitrobenzoate coordination modes

The solid state reaction of [Ca(H₂O)₄(η¹-4-nba)(η²-4-nba)] 1 (4-nba = 4-nitrobenzoate) with 2-methylimidazole (L²) at 100 °C results in the formation of a Ca(II) coordination polymer [Ca(H₂O)(L²)(4-nba)₂]_n2. Compound 2 was characterized by elemental analysis, spectral and thermal methods, and its structure determined. The coordination polymer 2 crystallizes in the centrosymmetric monoclinic space group P2₁/n with all atoms situated in general positions and its structure consists of a central Ca(II), a monodentate 2-methylimidazole, a bridging water ligand (μ₂-H₂O), a bidentate bridging (μ₂-η¹:η¹) 4-nba ligand and a monoatomic bridging (μ₂-η²) 4-nba ligand. Each seven-fold coordinated Ca(II) in the title compound is bonded to a nitrogen atom of a terminal 2-methylimidazole (L²) ligand, two symmetry related water molecules and four symmetry related 4-nba ligands, resulting in a distorted pentagonal bipyramidal {CaO₆N} polyhedron. Due to the bridging nature of the aqua and 4-nba ligands [(2-methylimidazole)calcium(II)] units in 2 are linked into a one-dimensional coordination polymer consisting of three chains, all of which propagate along b-axis. In the triple chain coordination polymer a Ca···Ca separation of 3.8432(3) Å is observed between neighbouring Ca(II) ions. The oxygen atoms of the carboxylate and nitro functionalities of the 4-nba ligand and the coordinated water are involved in O–H···O, N–H···O and C–H···O interactions. A comparative study of nine alkaline-earth 4-nitrobenzoate compounds is described.     

Molecular sheets in the crystal structure of a Ba(II) complex with imidazole-4,5-dicarboxylate and water ligands

The structure of poly-tetraaquabis(μ-Himidazole-4,5-dicarboxylato-N,O;-O′)barium(II) dihydrate, Ba(C₅H₃N₂O₄)₂(H₂O)₄·2H₂O is built of molecular sheets in which singly-deprotonated imidazole-4,5-dicarboxylate [H(4,5-IDA)] bridges metal ions using its N, O bonding moiety and one oxygen atom of its second carboxylate group. Each barium(II) is coordinated by N, O bonding moieties of two ligands, two carboxylate oxygen atoms of two other ligands and four waters. The coordination number of Ba(II) is ten, and the coordination polyhedron contains fourteen faces. A network of hydrogen bonds is responsible for the stability of the crystal.     

Dimerization and Coordination Properties of Zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine in Relation to DABCO in <Emphasis Type="Italic">o</Emphasis>-Xylene and Chloroform

For the first time the interactions between zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc) and 1,4-diazabicyclo[2.2.2]octane (DABCO) in o-xylene and chloroform have been studied by calorimetric titration and NMR and electron absorption spectroscopic methods. It has been found that in o-xylene at concentrations of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc higher than 6×10⁻⁴ mol⋅L⁻¹ π–π dimers species are formed (λ _max= 685 nm). Additions of DABCO to the solution up to mole ratio 1 : 8 (Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc : DABCO) lead to a shift of the aggregation equilibrium towards monomer species due to formation of monoligand axial complexes. Further increasing the DABCO concentration results in formation of Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc—DABCO—Zn(4—O—CO—C₆H₄—OC₁₁H₂₃)Pc sandwich dimers (λ _max= 675 nm).     

Etude des systemes CaHPO4−MHPO4−H2O (M=Sr,Ba) A 50°C

The systems CaHPO₄−MHPO₄−H₂O (M=Sr, Ba) were studied at 50°C. ForM=Sr, the series of single phases, Ca_1−xSr_xHPO₄ for 0.95<X<0.75 and Ca_xSr_1−xHPO₄ for 0.4<X<1 have been prepared. These solid solution were caracterized by their infrared spectra and their crystallographic unit cell parameters. ForM=Ba a new phase Ca₂Ba(HPO₄)₃ has been determined. It was characterized by DRX, IR, ATD and chemical analyses.

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Zusammenfassung Bei 50°C wurde das System CaHPO₄−MHPO₄−H₂O (mitM=Sr, Ba) untersucht. FürM=Sr wurden Serien von Einzelphasen erhalten: Ca_1−xSr_xHPO₄ für 0.95<X< 0.75 und Ca_xSr_1−xHPO₄ für 0.4<X<1. Diese Mischkristalle wurden anhand ihrer Infrarotspektren und ihrer kristallographischen Elementarzellenparameter charakterisiert. FürM=Ba wurde die neue Phase Ca₂Ba(HPO₄)₃ ermittelt. Sie wurde mittels DRX, IR, ATD und chemischer Analyse charakterisiert.

     

Synthesis, spectroscopy and supramolecular structures of two magnesium 4-nitrobenzoate complexes

The aqueous reaction of [Mg(H₂O)₆]Cl₂ with the in situ generated sodium salt of 4-nitro-benzoic acid (4-nbaH) and N-methylimidazole (N-MeIm) results in the formation of the dinuclear complex [Mg(H₂O)(N-MeIm)₂(4-nba)₂]₂ 1 (4-nba = 4-nitro benzoate), while the direct reaction of [Mg(H₂O)₆]Cl₂ with sodium 4-nba leads to the formation of the mononuclear complex, [Mg(H₂O)₆](4-nba)₂·2H₂O 2. In the centrosymmetric dimer 1, each Mg atom is coordinated to an aquo ligand, two monodentate N-MeIm ligands and a monodentate 4-nba ligand. The second 4-nba ligand functions as a bridging bidentate ligand, linking the metal centers and completes the hexacoordination around each Mg(II). The dimeric molecules of 1 are linked into a one-dimensional chain along b with the aid of intra-as well as intermo-lecular H-bonding interactions between the coordinated water and the free oxygen atom of the monodentate 4-nba ligand. In the mononuclear complex [Mg(H₂O)₆](4-nba)₂·2H₂O 2, the Mg(II) is located on an inversion center and its structure consists of an octahedral [Mg(H₂O)₆]²⁺ dication, a free uncoordinated 4-nba anion and a lattice water molecule. One of the H atoms attached of the lattice water is disordered over two positions. The hexaaquomagnesium(II) dication, the 4-nba anion and the lattice water molecule are linked by intra- and intermolecular H-bonding interactions resulting in the formation of alternating layers of [Mg(H₂O)₆]²⁺ dications and 4-nba anions in the crystallographic bc plane. The lattice water molecules are situated between the cations, while the 4-nba anions are arranged antiparallel to each other along b. Dedicated to Prof. Dr. Werner Weisweiler on the occasion of his 69th birthday     

Synthesis, spectroscopy, thermal studies and supramolecular structures of two new alkali-earth 4-nitrobenzoate complexes containing coordinated imidazole

The reaction of hydrated magnesium or calcium 4-nitrobenzoate (4-nba) generated in situ, with imidazole (Im) results in the formation of the complexes [Mg(H₂O)₂(Im)₂(4-nba)₂] 1 and [Ca(H₂O)₃(Im)(4-nba)₂]·Im 2, which exhibit the same metal:4-nba:Im ratio but different degrees of hydration. Complex 1 crystallizes in the triclinic Pī space group and the Mg atom is located on an inversion centre, while 2 crystallizes in the monoclinic P2₁/c space group and all atoms are located in general positions. In 1 the Im ligands, which are trans to each other, are coordinated to Mg, while 2 contains coordinated as well as free Im. The monodentate 4-nba ligands are disposed trans to each other in 1, while they adopt a cis orientation in 2 resulting in different supramolecular structures. Complex 1 exhibits two types of H-bonding interactions namely O-H···O and N-H···O, while in 2 three varieties of H-bond, viz. O-H···O, N-H···O and O-H···N are observed. The Im ligand ligand functions as a bifurcated H-bond donor in 1 while the O atom of the nitro group functions as a H-bond acceptor. In contrast, the nitro group in 2 is not involved in any H-bonding interactions. The free Im in 2 functions as a bifurcated acceptor and forms an extended chain linking adjacent complex molecules. The chains thus formed are further cross-linked with the aid of H-donor bonds from both the free as well as the coordinated Im. Both 1 and 2 exhibit π-π stacking interactions. Complex 1 is thermally more stable as compared to 2, and both complexes can be dehydrated to the corresponding anhydrous complexes by heating at 140 and 100°C respectively. At elevated temperatures, both the complexes can be pyrolysed to the corresponding oxide. The anhydrous complexes can be rehydrated to obtain the starting hydrated materials.     

Low-temperature heat capacities and standard molar enthalpy of formation of the complex

Low-temperature heat capacities of a solid complex Zn(Val)SO₄·H₂O(s) were measured by a precision automated adiabatic calorimeter over the temperature range between 78 and 373 K. The initial dehydration temperature of the coordination compound was determined to be, T _D=327.05 K, by analysis of the heat-capacity curve. The experimental values of molar heat capacities were fitted to a polynomial equation of heat capacities (C _p,m) with the reduced temperatures (x), [x=f (T)], by least square method. The polynomial fitted values of the molar heat capacities and fundamental thermodynamic functions of the complex relative to the standard reference temperature 298.15 K were given with the interval of 5 K. Enthalpies of dissolution of the [ZnSO₄·7H₂O(s)+Val(s)] (Δ_sol H _m,l ⁰) and the Zn(Val)SO₄·H₂O(s) (Δ_sol H _m,2 ⁰) in 100.00 mL of 2 mol dm^–3 HCl(aq) at T=298.15 K were determined to be, Δ_sol H _m,l ⁰=(94.588±0.025) kJ mol^–1 and Δ_sol H _m,2 ⁰=–(46.118±0.055) kJ mol^–1, by means of a homemade isoperibol solution–reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as: Δ_f H _m ⁰ (Zn(Val)SO₄·H₂O(s), 298.15 K)=–(1850.97±1.92) kJ mol^–1, from the enthalpies of dissolution and other auxiliary thermodynamic data through a Hess thermochemical cycle. Furthermore, the reliability of the Hess thermochemical cycle was verified by comparing UV/Vis spectra and the refractive indexes of solution A (from dissolution of the [ZnSO₄·7H₂O(s)+Val(s)] mixture in 2 mol dm^–3 hydrochloric acid) and solution A’ (from dissolution of the complex Zn(Val)SO₄·H₂O(s) in 2 mol dm^–3 hydrochloric acid).