Ishtvan Boldog

Highly stable nanoporous covalent triazine-based frameworks with an adamantane core for carbon dioxide sorption and separation

Adamantane substituted with two to four 4-cyanophenyl groups was used for preparation of a new series of robust Porous Covalent Triazine-based Framework (PCTF) materials. Novel adamantane PCTFs were synthesized in good yields (>80%) by the trimerization reaction of 1,3-bis-, 1,3,5-tris- and 1,3,5,7-tetrakis(4-cyanophenyl)adamantane, respectively, in the presence of ZnCl2 (Lewis acid condition) and CF3SO3H (strong Bronsted acid condition). From N2 adsorption isotherms, the Lewis acid condition gives higher surface areas than the strong Bronsted acid condition. The amorphous nano- to microporous frameworks (>50% micropore fraction) exhibit excellent thermal stabilities (>450 °C) with BET surface areas up to 1180 m2 g−1. A very similar ultramicropore size distribution between 4 and 10 A was derived from CO2 adsorption isotherms with a “CO2 on carbon based slit-pore model”. At 1 bar the gases H2 (at 77 K), CO2 (at 273 and 293 K) and CH4 (at 273 K) are adsorbed up to 1.24 wt%, 58 cm3 g−1 and 20 cm3 g−1, respectively. Gas uptake increases with BET surface area and micropore volume which in turn increase with the number of cyano groups in the monomer. From single component adsorption isotherms, IAST-derived ideal CO2:N2, CO2:CH4 and CH4:N2 selectivity values of up to 41u2006:u20061, 7u2006:u20061 and 6u2006:u20061, respectively, are calculated for p → 0 at 273 K. The adamantane PCTFs have isosteric heats of adsorption for CO2 of 25–28 kJ mol−1 at zero loading and most of them also >25 kJ mol−1 over the entire adsorption range which is well above the heat of liquefaction of bulk CO2 or the isosteric enthalpy of adsorption for CO2 on activated carbons.

Bifunctional pyrazolate–carboxylate ligands for isoreticular cobalt and zinc MOF-5 analogs with magnetic analysis of the {Co4(μ4-O)} node

The ditopic ligands 3,5-dimethyl-pyrazolate-4-carboxylate, –Me2pzCO2–, and 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoate, –Me2pzC6H4CO2–, combine a pyrazolate and carboxylate functionality in axial orientation and lead to porous cobalt or zinc azolate–carboxylate frameworks that have the same cubic pcu-a topology and {M4(μ4-O)} nodes (M = Co, Zn) as MOF-5 and other IRMOFs. The microporous networks [M4(μ4-O)(Me2pzCO2)3] (M = Co, Zn) with the short linker exhibit a solvent-induced gate effect, evidenced by gas desorption hysteresis due to small pore apertures of 2.8 A diameter together with small amounts of high-boiling solvent remaining in the activated samples. For [Co4(μ4-O)(Me2pzCO2)3], the low-pressure H2 storage capacity (1.7 wt%, 1 bar , 77 K) is higher than for MOF-5, and the CO2 uptake of 20.8 wt% puts it among the top MOFs for low-pressure CO2 sorption even though the BET surface is less than 1000 m2 g−1. The analysis of the magnetic properties of [Co4(μ4-O)(Me2pzCO2)3] takes into account the distribution of tetrahedra resulting from the disorder of the pyrazolate–carboxylate linker. An antiferromagnetic coupling observed for [Co4(μ4-O)(Me2pzCO2)3] arises from the interactions of the cobalt(II) ions through the combined μ4-O + syn–syn carboxylate and μ4-O + pyrazolate bridges.

Novel Coordination Frameworks Incorporating the 4,4′-Bipyrazolyl Ditopic Ligand

The reaction of the rigid spacer 4,4-bipyrazole (H(2)BPZ) with late transition metals, either following conventional routes or under solvothermal conditions, afforded the coordination polymers [M(BPZ)]·Solv (M = Zn, 1; Co, 2; Cd, 3; Hg, 4; Cu, 5; Ni, 6; Pd, 7; Solv = DMF, 3; MeCN, 5 and 6; H(2)O, 7), [Cu(H(2)BPZ)(2)(NO(3))(2)] (8), and [Cd(H(2)BPZ)(CH(3)COO)(2)] (9). State-of-the-art laboratory powder diffraction methods allowed to disclose the isomorphous character of 1 and 2, as well as of 5 and 6, which feature 3D porous networks containing 1D channels of square and rhombic shape, respectively. 3, crystallizing in the relatively rare P6(1)22 space group, consists of homochiral helices of octahedral Cd(II) ions, packing in bundles mutually linked by radial, nonplanar BPZ ligands. Finally, the dense species 8 and 9 contain parallel 2D layers of square and rectangular meshes, respectively. Thermogravimetric analyses witnessed the relevant thermal robustness of all the [M(BPZ)] materials [except the mercury(II) derivative], which are stable in air at least up to 300 °C, with the zinc(II) derivative decomposing only around 450 °C. Variable-temperature powder diffraction experiments highlighted the permanent porosity of 1-3, 5, and 6, retained along consecutive temperature cycles in all cases but 3. When probed with N(2) at 77 K, 1-3 and 5-7 showed Brunauer-Emmett-Teller and Langmuir specific surface areas in the ranges 314(2)-993(11) and 509(16)-1105(1) m(2)/g, respectively.

A rare alb-4,8-Cmce metal–coordination network based on tetrazolate and phosphonate functionalized 1,3,5,7-tetraphenyladamantane

Symmetric tetrahedral ligands are prominent, but somewhat under-investigated building blocks for the generation of coordination polymeric networks. Coordination networks [Mn5Cl2(L1)2(H2O)4(DMF)4]·3H2O·7DMF, 1 and the [La2(H5L2)2(H2O)6], 2 are synthesized under mild solvothermal methods in DMF from the adamantane-based tetrahedral ligands, 1,3,5,7-tetrakis(4-phenyltetrazol-5-yl)adamantane (H4L1), reported for the first time, and 1,3,5,7-tetrakis(4-phenylphosphonic acid)adamantane (H8L2), respectively. Compounds 1 and 2 are based on completely different pentanuclear and binuclear secondary metal building units, respectively, and have different symmetries, but demonstrate an interesting coincidence of underlying topologies, which could be interpreted as a directing or ‘imprinting’ effect of the symmetry of the rigid tetrahedral ligands. Both structures represent examples of a rarely observed (4,8)-coordinated net. The χMT product for 1 at room temperature is slightly lower than the expected for five Mn(II) ions with S = 5/2 and g ≈ 1.98 and on lowering the temperature χMT approaches the expected value for a single Mn(II) as a result of the antiferromagnetic coupling through the tetrazolate bridges.

Water effect on the spin-transition behavior of Fe(II) 1,2,4-triazole 1D chains embedded in pores of MCM-41

The spin-crossover (SCO) compounds [Fe(Htrz)3](BF4)2·H2O (SCO-1) and [Fe(Htrz)2trz]BF4 (SCO-2) (Htrz = 1,2,4-triazole) were embedded in the pores of mesostructured silica MCM-41 to yield SCO@MCM composites as evidenced by electron microscopy, gas sorption studies, powder X-ray diffractometry, atomic absorption and infrared spectrometry. Studies of the temperature-induced spin crossover behavior of the composites by temperature-variable 57Fe Mossbauer spectroscopy, magnetic and differential scanning calorimetry measurements and optical reflectivity indicate that the spin transition of the composites was significantly shifted for SCO-1@MCM to higher temperature in comparison to bulk SCO-1 compounds while the shift for SCO-2 was negligible. These shifts in the transition temperature for SCO-1@MCM [versus bulk SCO-1] amounted to T↑c = 371/376 K [282/291 K] and T↓c = 340/345 K [276/286 K] (magnetic/optical reflectivity data) with a broadening of the hysteresis by 25–26 K relative to bulk SCO-1 (varying slightly with the used method). The significant difference in the SCO behavior of the similar materials SCO-1 and SCO-2 when embedded in the MCM-41 matrix is assigned to the hydration of the SCO-1@MCM material. Water is apparently crucial in transmitting the confinement pressure or matrix effect on the spin transition when the SCO compound is embedded between the pore walls.

A fluorite isoreticular series of porous framework complexes with tetrahedral ligands: new opportunities for azolate PCPs

Three porous coordination polymers with a simplified formula of [M4(μ4-Cl)L2]·nGuest (M = Cu, Cd) based on two adamantane-derived tetrahedral tetrazolate ligands were synthesized. Along with one known representative, the row of compounds establishes a new isoreticular series with fluorite as the underlying net.

Modular construction of 3D coordination frameworks incorporating SiF62− links: Accessing the significance of [M(pyrazole)4{SiF6}] synthon

Rational combination of Cd2+ cations, bitopic pyrazole ligands, bridging SiF62− and terminal NCS− anions provide generation of 3D frameworks and precise control over connectedness of the net nodes: two-fold interpenetrated 4-connected NbO-like net (nbo) in [Cd(Me4bpz)2{NCS}2]·⅔CH2Cl2 (1), uninodal 5-connected noz framework in [Cd2(Me4bpz)4{SiF6}{NCS}2]·6CHCl3 (2), novel 5-connected binodal topology (with a point symbol of {42.55.62.7}{42.56.62}) in [Cd2(Me4bpz)4{SiF6}{NCS}2]·2CH2Cl2 (3) and 6-connected α-Po cubic nets (pcu) in [Cd(Me4bpz)2{SiF6}]·6H2O (4) and [Cd(Me4bpz)2{SiF6}]·1.5CH2Cl2 (5) (Me4bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole). Hexafluorosilicate anions act as bridges between Cd ions yielding further linkage of 4-connected [Cd(Me4bpz)2] subtopologies. Characteristic and specific interaction between SiF62− and the metal–organic portion is conditioned by a synergy of coordination and multiple strong NH⋯F bonds, which suggests perfect compatibility of the bipyrazole and SiF62− linkers for the construction of 3D structures, either by pillaring of 2D layers or cross-linking of 3D frameworks. Two observed motifs, 1D [M(pyrazole)4{μ-SiF6}]n (in 4 and 5) and discrete [{M{NCS}(pyrazole)4}2{μ-SiF6}] (in 2 and 3) are discussed as special supramolecular synthons for the framework solids. An improved large-scale and cost-effective procedure for the synthesis of the organic ligand Me4bpz is also described.

A view on systematic truncation of tetrahedral ligands for coordination polymers

Bis-, tris- and tetrakis(carboxyphenyl)adamantanes were probed for the synthesis of coordination polymers of d-metals, with a successful outcome for Mn, Co, and Cd. Formation of sql, hcb and dia frameworks based on small clusters demonstrates the dominant role of the ligand shape in defining the outcome of crystallization.

1,3,5-Triphenyladamantane and 1,3,5,7-tetraphenyladamantane.

In 1,3,5-triphenyladamantane, C(28)H(28), (I), and 1,3,5,7-tetraphenyladamantane, C(34)H(32), (II), the molecules possess symmetries 3 and 4, and are situated across threefold and fourfold improper axes, respectively. The molecules aggregate by means of extensive C-H...pi interactions. In (I), the pyramidal shape of the molecules dictates the formation of dimers through a ;sixfold phenyl embrace pattern. The dimers are linked to six close neighbors and constitute a primitive cubic net [H...pi = 2.95 (2) and 3.02 (2) A]. Compound (II) is isomorphous with tetraphenyl derivatives EPh(4) of group 14 (E = C-Pb) and ionic salts [EPh(4)][BPh(4)] (E = P, As and Sb). The multiple C-H...pi interactions arrange the molecules into chains, with a concerted action of CH (phenyl) and CH(2) (adamantane) groups as donors [H...pi = 3.15 (2) and 3.44 (2) A, respectively]. The additional interactions with the methylene groups (four per molecule) are presumably important for explaining the high melting point and insolubility of (II) compared with the EPh(4) analogs.

Coordination polymers of CoII and 3,3′,5,5′-tetramethyl-4,4′-bipyrazolyl: a novel metal–organic three-dimensional network with four-coordinated planar vertices

The bitopic exodentate ligand 3,3′,5,5′-tetramethyl-4,4′-bipyrazolyl (4,4′-bpz), designed as an angular bridging unit capable of formation of a set of coordination and hydrogen bonds, gave the coordination polymers [Co(4,4′-bpz)2{C6H5CO2}2]·2C6H5Br 1 and [Co(4,4′-bpz){C6H5CO2}{CH3CO2}]·2C6H5Br 2. Complex 1 exhibits a 3-D structure containing rectangular channels. The topology of the array has no precedents in crystal engineering of linear spacer ligands of the 4,4′-bipyridine type and may be a prototype for engineering of a novel family of functional solids. Complex 2 exists as a hybrid coordination/hydrogen-bonded porous network which incorporates two guest bromobenzene molecules per metal atom.