Inclusion of Ln(III) in the Complexes of Co(II) with a Mannich Base Ligand: Development of Atmospheric CO2 Fixation and Enhancement of Catalytic Oxidase Activities.

The reaction of the Mannich base ligand (H2L = N, N'-dimethyl- N, N'-bis(2-hydroxy-3-methoxy-5-methylbenzyl)ethylenediamine) with Co(OAc)2·4H2O and Ln(III) nitrate salts (Ln = Gd, Tb, and Dy) under basic conditions afforded three carbonato-bridged isostructural tetranuclear heterometallic Co(II)-Ln(III) complexes (Co2Gd2L2(µ4-CO3)2(NO3)2] (1), [Co2Tb2L2(µ4-CO3)2(NO3)2] (2), and [Co2Dy2L2(µ4-CO3)2(NO3)2] (3)) by atmospheric CO2 fixation. In all structures, two dinuclear [(CoIIL)LnIII(NO3)] units are linked via two µ4-carbonato groups to form the tetranuclear CoII2LnIII2 core. The geometry around two penta-coordinated Co(II) ions is distorted square pyramid, and that around two nona-coordinated Ln(III) ions is intermediate between "spherical tricapped trigonal prism" and "spherical capped square antiprism" in all complexes. The complexes (1-3) showed catecholase-like and phenoxazinone-synthase-like catalytic activities. The kcat values calculated for the catecholase-like reaction were 254.5, 272.4, and 291.3 h-1, and for the phenoxazinone-synthase-like reaction they were 2930.6, 2965.2, and 2998.5 h-1 for complexes 1-3, respectively. The probable pathways for these two oxidase reactions have been proposed by the analyses of mass spectral data. For all of the compounds, the variable temperature magnetic susceptibility and isothermal magnetization data were investigated. The complexes exhibited overall ferromagnetic behavior, which was evident from the isothermal magnetization curves. AC magnetic susceptibility measurements revealed the slow relaxation of magnetization in complexes 2 and 3 but very negligible in 1. The activation energy barriers ( Ueff) for the slow relaxation process were evaluated and found to be 1.99, 2.79, and 8.98 K for 1, 2, and 3, respectively.

Single crystal to single crystal (SC-to-SC) transformation from a nonporous to porous metal-organic framework and its application potential in gas adsorption and Suzuki coupling reaction through postmodification.

A new amino-functionalized strontium-carboxylate-based metal-organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC-to-SC) transformation upon desolvation. Both structures have been characterized by single-crystal X-ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent -NH2 groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine-2-carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross-coupling reaction. The compound shows high activity towards the C-C cross-coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m(2) g(-1). The material also possesses good CO2 (8 wt %) and H2 (1.87 wt %) adsorption capabilities.

pH-Tuned Modulation of 1D Chain to 3D Metal-Organic Framework: Synthesis, Structure and Their Useful Application in the Heterogeneous Claisen-Schmidt Reaction.

The role of pH in the formation of metal-organic frameworks (MOFs) has been studied on magnesium-based carboxylate framework systems [Mg(Pdc)(H2 O)3 ]n (1) and [Mg(Pdc)(H2 O)]n (2) (Pdc=pyridine-2,3-dicarboxylate). The investigation reveals the formation of two different compounds of one- or three-dimensions starting from the same reaction mixture that differs only in pH. Isolated compounds have been characterized by IR and elemental analysis; both compounds were also successfully characterized by single-crystal X-ray diffraction. This study shows that the gradual increase in pH helps to construct a higher-dimensional network. Catalytic activity of compounds 1 and 2 was tested for the Claisen-Schmidt reaction. Compound 2 was successfully dehydrated to produce a coordinately unsaturated compound 2 a, which shows higher catalytic activity than 1 or 2 in heterogeneous medium.

Layered transition metal carboxylates: synthesis, structural aspects and observation of multi-step magnetic transition through phase diagram.

Two new layered transition metal carboxylate frameworks, [Co3(L)2(H2O)6]·2H2O () and [Ni3(L)2(H2O)6]·2H2O () (L = tartronate anion or hydroxymalonic acid), have been synthesized and characterized by X-ray single crystal analysis. Both compounds have similar 2D structures. In both compounds there are two types of metal centers where one center is doubly bridged by the alkoxy oxygen atoms through µ2-O bridging to form a 1D infinite chain parallel to the crystallographic b-axis with the corners shared between the metal polyhedra. Magnetic susceptibility measurements revealed the existence of antiferromagnetic short range correlations between Co(Ni) intra-chain metal centers (with exchange constants JCo = -22.6 and JNi = -35.4 K). At low temperatures, long range order is observed in both compounds at Néel temperatures of 11 (for ) and 16 (for ) K, revealing that other exchange interactions, rather than the intra-chain ones, play a role in these systems. Whereas compound has an antiferromagnetic ground state, compound exhibits a ferromagnetic component, probably due to spin canting. Isothermal magnetization data unveiled a rich phase diagram with three metamagnetic phase transitions below 8 K in compound .

Anchoring of palladium onto surface of porous metal-organic framework through post-synthesis modification and studies on Suzuki and Stille coupling reactions under heterogeneous condition.

An ecofriendly solid catalyst has been synthesized by anchoring palladium(II) into post synthetically modified metal organic framework IRMOF-3. The pore of IRMOF-3 was first modified with pyridine-2-aldehyde. The amine group of IRMOF-3 upon condensation with pyridine-2-aldehyde afforded a bidentate Schiff base moiety in the porous matrix. The Schiff base moieties were used to anchor palladium(II) ions. The prepared catalyst has been characterized by UV-vis, IR spectroscopy, X-ray powder diffraction, and nitrogen sorption measurements. Framework structure of the catalyst is not being destroyed in the multistep synthesis procedure as evidenced in X-ray powder diffraction studies. The catalyst has shown high activity toward the Suzuki and Stille cross-coupling reaction in 20% H2O/EtOH and EtOH medium, respectively, at 80 °C. The immobilized complex did not leach or decompose during the catalytic reactions, showing practical advantages over the homogeneous catalysis.

Porous magnesium carboxylate framework: synthesis, X-ray crystal structure, gas adsorption property and heterogeneous catalytic aldol condensation reaction.

A new three-dimensional alkaline-earth metal-organic framework (MOF) compound, [Mg(Pdc)(H(2)O)](n) (1) (H(2)Pdc = pyridine-2,5-dicarboxylic acid), has been synthesized and structurally characterized by single crystal X-ray diffraction analysis. Compound 1 features a 3D porous framework afforded by the Mg(2)-diad centers through formation of interconnected chair like structural motifs. A nitrogen adsorption study confirms the microporosity of compound 1 with a BET surface area of 211 ± 12 m(2) g(-1). Upon dehydration, the BET surface area of 1 is enhanced to a value of 463 ± 36 m(2) g(-1) due to removal of coordinated water molecule. After rehydration, the compound reverts to its original form as evidenced by powder X-ray diffraction and IR spectroscopic analysis and N(2) sorption measurement. Compound 1 retains its pore structure with a variable BET surface area in several cycles of dehydration and rehydration processes indicating robustness of the framework in [Mg(Pdc)(H(2)O)](n) (1). Compound 1 catalyzes the aldol condensation reactions of various aromatic aldehydes with acetone and cyclohexanone in heterogeneous conditions. Notably, the catalytic activity of the compound is enhanced upon dehydration. The catalyst can be recycled and reused several times without significant loss of activity.

Controlled construction of metal-organic frameworks: hydrothermal synthesis, X-ray structure, and heterogeneous catalytic study.

The role of pH in the formation of metal-organic frameworks (MOFs) has been studied for a series of magnesium-based carboxylate framework systems. Our investigations have revealed the formation of five different zero-dimensional (0D) to three-dimensional (3D) ordered frameworks from the same reaction mixture, merely by varying the pH of the medium. The compounds were synthesized by the hydrothermal method and characterized by single-crystal X-ray diffraction. Increase of the pH of the medium led to abstraction of the imine hydrogen from the ligand and a concomitant increase in the OH(-) ion concentration in the solution, facilitating the construction of higher dimensional framework compounds. A stepwise increase in pH resulted in a stepwise increase in the dimensionality of the network, ultimately leading to the formation of a 3D porous solid. A gas adsorption study of the 3D framework compound confirmed its microporosity with a BET surface area of approximately 450 m(2) g(-1). Notably, the 3D framework compound catalyzes aldol condensation reactions of various aromatic aldehydes with acetone under heterogeneous conditions.

Bis(2,2'-bipyridine-κ(2)N,N')bis-(dicyan-amido-κN(1))cadmium.

In the title compound, [Cd(C(2)N(3))(2)(C(10)H(8)N(2))(2)], the Cd(II) ion is coordinated in a distorted octa-hedral environment by four N atoms from two chelating 2,2'-bipyridine ligands and two N atoms from two monodentate dicyanamide ligands. The dihedral angle between the mean planes of the two bipyridine ligands is 87.67 (6)°.

Tetra-aqua-bis-[2-(pyridin-4-yl-κN)pyrimidine-5-carboxyl-ato]zinc.

In the title complex, [Zn(C(10)H(6)N(3)O(2))(2)(H(2)O)(4)], the Zn(II) ion lies on an inversion center and is coordinated in a slightly distorted octa-hedral geometry by two N atoms from two 2-(pyridin-4-yl)pyrimidine-5-carboxyl-ate ligands and four water mol-ecules. In the symmetry-unique part of the mol-ecule, the pyridine and pyrimidine rings form a dihedral angle of 7.0 (1)°. In the crystal, the coordinating water mol-ecules act as donor groups and carboxyl-ate O atoms act as acceptors in O-H⋯O hydrogen bonds, forming a three-dimensional network.

Entrapment of [Ru(bpy)3]2+ in the anionic metal-organic framework: novel photoluminescence behavior exhibiting dual emission at room temperature.

[Ru(bpy)(3)](2+) (bpy = 2,2'-bipyridine) ions were entrapped into the cavities of two-dimensional anionic sheet-like coordination polymeric networks of [M(dca)(3)](-) (dca = dicyanamide; M = Mn(II) and Fe(II)). The prepared compounds, {[Ru(bpy)(3)][Mn(dca)(3)](2)}(n) (1) and {[Ru(bpy)(3)][Fe(dca)(3)](2)}(n) (2), were structurally characterized by X-ray single crystal analysis. The spectroscopic properties of the [Ru(bpy)(3)](2+) ion dramatically changed on its entrapment in [M(dca)(3)](-). The [Ru(bpy)(3)](2+) moiety present in 1 and 2 exhibits novel dual photo-emission at room temperature.

Layered transition metal carboxylates: efficient reusable heterogeneous catalyst for epoxidation of olefins.

Layered metal carboxylates [M(malonato)(H(2)O)(2)](n) (M = Ni(II) and Mn(II)) that have a claylike structure have been synthesized hydrothermally and characterized. The interlayer separation in these layered carboxylates is comparable to that of the intercalation distance of the naturally occurring clay materials or layered double hydroxides (LDHs). In this study, we have demonstrated that, instead of intercalating the metal complex into layers of the clay or LDH, layered transition metal carboxylates, [M(malonato)(H(2)O)(2)](n), as such can be used as a recyclable heterogeneous catalyst in olefin epoxidation reaction. Metal carboxylates [M(malonato)(H(2)O)(2)](n) exhibit excellent catalytic performance in olefin epoxidation reaction.

Oxo-vanadium(IV) dihydrogen phosphate: preparation, magnetic study, and heterogeneous catalytic epoxidation.

A layered oxo-vanadium(IV) dihydrogen phosphate, {VO(H2PO 4)2} n has been synthesized hydrothermally and characterized by several physicochemical methods. Single-crystal X-ray analysis (crystal system, tetragonal; space group, P4/ ncc; unit cell dimensions, a = b = 8.9632(4), c = 7.9768(32) A) of {VO(H2PO4) 2} n reveals that the compound has an extended two-dimensional structure. The VO2+ moieties are connected through bridging H 2PO4 (-) ions, and this type of connection propagates parallel to the crystallographic ab plane which gives rise to a layered structure. The layers are staked parallel to the crystallographic c axis with a separation between the layers of ca. 4.0 A. Magnetic susceptibility of {VO(H2PO4)2} n has been measured in the temperature range 2-300 K on a SQUID magnetometer. The magnetic property of {VO(H2PO4)2} n is explicable in the light of a two-dimensional quantum Heisenberg antiferromagnet model. Magnetic pathways are available through the dihydrogen-phosphato bridges within the layer and provide for weak antiferromagnetic interactions. Notably {VO(H2PO4)2} n catalyzes the epoxidation reaction of alkenes with tert-BuOOH in acetonitrile medium under heterogeneous condition.