Beatriz Gil-Hernández

Spontaneous resolution upon crystallization of chiral La(III) and Gd(III) MOFs from achiral dihydroxymalonate

The achiral chelating and bridging dihydroxymalonato (mesoxalato) ligand is a new enantiopurity enforcer in extended structures by yielding the Λ/Δ-metal configured homochiral MOFs 2D-[Ln(2)(μ-mesoxalato)(3)(H(2)O)(6)] (Ln = La(III), Gd(III)) through self-resolution during crystal growth.

Magnetic Ordering in Two Molecule-Based (10,3)-a Nets Prepared from a Copper(II) Trinuclear Secondary Building Unit

Two new molecule-based materials of formulas 3D-{[K(H(2)O)(6)](0.5)[K(18-crown-6)](0.5)[MnCu(3)(Hmesox)(3)].5.25H(2)O} (1) and 3D-{(Ph(4)P)(2)[MnCu(3)(Hmesox)(3)Cl].3.5H(2)O} (2) have been prepared from a tricopper(II) secondary building unit (SBU), [Cu(3)(Hmesox)(3)](3-) (H(4)mesox = mesoxalic acid, 2-dihydroxymalonic acid). Compound 1 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of potassium cations and the 18-crown-6 ether, whereas compound 2 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of Ph(4)PCl. The [MnCu(3)(Hmesox)(3)](-) and [MnCu(3)(Hmesox)(3)Cl](2-) moieties in compounds 1 and 2, respectively, yield chiral 3-connected three-dimensional (3D) anionic (10,3)-a (srs, SrSi(2)) nets. In the cubic and centrosymmetric structures (Pa3) of 1, two inversion-symmetry-related anion nets interpenetrate to a racemic structure. The Ph(4)P(+) cations in 2 are organized in a supramolecular (10,3)-a net through the 6-fold phenyl embrace. In 2, both the cationic and anionic nets are homochiral and enantiopure with opposite handedness and form interpenetrating supramolecular and covalent (10,3)-a nets in the noncentrosymmetric Sohncke space group P 2(1)2(1)2(1). Both compounds display ferrimagnetic interaction with long-range magnetic ordering below 2.5 and 15.2 K for 1 and 2, respectively. A dehydrated phase of 2 exhibits a T(c) of 21.8 K. The saturation of magnetization, M(S), indicates two different ground states, S = (1)/(2) and (3)/(2), for the tricopper(II) units in 1 and 2, respectively. The different spin states of the tricopper(II) unit in 1 and 2 has been explained by means of a density functional theory (DFT) study performed in the [Cu(3)(Hmesox)(3)](3-) and [Cu(3)(Hmesox)(3)Cl](4-) fragments, for 1 and 2, respectively. A further DFT study has allowed one to analyze the structural parameters that lead to the different spin ground states for the trinuclear units in both compounds.

Self-Assembled 3D Heterometallic CuII/FeII Coordination Polymers with Octahedral Net Skeletons: Structural Features, Molecular Magnetism, Thermal and Oxidation Catalytic Properties

The new three-dimensional (3D) heterometallic Cu(II)/Fe(II) coordination polymers [Cu(6)(H(2)tea)(6)Fe(CN)(6)](n)(NO(3))(2n)·6nH(2)O (1) and [Cu(6)(Hmdea)(6)Fe(CN)(6)](n)(NO(3))(2n)·7nH(2)O (2) have been easily generated by aqueous-medium self-assembly reactions of copper(II) nitrate with triethanolamine or N-methyldiethanolamine (H(3)tea or H(2)mdea, respectively), in the presence of potassium ferricyanide and sodium hydroxide. They have been isolated as air-stable crystalline solids and fully characterized including by single-crystal X-ray diffraction analyses. The latter reveal the formation of 3D metal-organic frameworks that are constructed from the [Cu(2)(μ-H(2)tea)(2)](2+) or [Cu(2)(μ-Hmdea)(2)](2+) nodes and the octahedral [Fe(CN)(6)](4-) linkers, featuring regular (1) or distorted (2) octahedral net skeletons. Upon dehydration, both compounds show reversible escape and binding processes toward water or methanol molecules. Magnetic susceptibility measurements of 1 and 2 reveal strong antiferromagnetic [J = -199(1) cm(-1)] or strong ferromagnetic [J = +153(1) cm(-1)] couplings between the copper(II) ions through the μ-O-alkoxo atoms in 1 or 2, respectively. The differences in magnetic behavior are explained in terms of the dependence of the magnetic coupling constant on the Cu-O-Cu bridging angle. Compounds 1 and 2 also act as efficient catalyst precursors for the mild oxidation of cyclohexane by aqueous hydrogen peroxide to cyclohexanol and cyclohexanone (homogeneous catalytic system), leading to maximum total yields (based on cyclohexane) and turnover numbers (TONs) up to about 22% and 470, respectively.

Homochiral lanthanoid(III) mesoxalate metal–organic frameworks: synthesis, crystal growth, chirality, magnetic and luminescent properties

The achiral chelating and bridging mesoxalato ligand (H2mesox2−), the conjugate base of mesoxalic or dihydroxymalonic acid (H4mesox), is a new enantiopurity enforcer in extended structures by yielding the Λ/Δ-metal configured homochiral MOFs 2D-[Ln2(μ-H2mesox)3(H2O)6], [with Ln(III) = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Er (10) and Yb (11)]; through self-resolution during crystallization. Single crystals of the compounds have been grown in agarose gel. All the compounds obtained are isostructural as deduced by means of single crystal and powder X-ray diffraction analysis and exhibit the Ln(III) ions covalently connected by the mesoxalato ligands into a corrugated grey arsenic-type (6,3)-net (or layer) with chair-shaped six-membered rings. Luminescence measurements reveal that the Eu(III) compound (6) exhibits several strong characteristic emission bands for isolated europium(III) ions in the visible region when excited between 350 and 420 nm; similarly the terbium(III) compound (8) displays the characteristic emission bands for isolated terbium(III) ions. Magnetic susceptibility measurements show deviations from the Curie law mainly owing to the split of the ground term due to the ligand field and spin–orbit coupling in the case of Sm(III) (4) and Eu(III) (6) compounds.

Copper(II) complexes with a new carboxylic-functionalized arylhydrazone of β-diketone as effective catalysts for acid-free oxidations

The aquasoluble [Cu(H2O)((CH3)2NCHO)(HL)] (2) and [Cu2(CH3OH)2(μ-HL)2] (3) CuII complexes were prepared by reaction of CuII nitrate hydrate with the new 3-(2-hydroxy-4-carboxyphenylhydrazone)pentane-2,4-dione (H3L, 1), in the presence (for 2) or absence (for 3) of (n-C4H9)2SnO, and characterized by elemental analysis, IR spectroscopy and X-ray single crystal diffraction. Magnetic susceptibility measurements, in compound 3, reveal strong antiferromagnetic coupling between the CuII ions through the μ2-phenoxido-O atoms, J = −203(1) cm−1. Complexes 2 and 3 act as catalyst precursors for the acid-free peroxidative oxidation of cyclohexane to the mixture of cyclohexyl hydroperoxide (primary product), cyclohexanol and cyclohexanone (TONs and yields up to 163 and 14.4%, respectively), as well as for the selective aerobic oxidation of benzyl alcohols to benzaldehydes in aqueous solution, mediated by a TEMPO radical, under mild conditions (TONs and yields up to 390 and 94%, respectively). In the alkane oxidations, 2 and 3 appear to behave as “dual role catalysts” combining, in one molecule, an active metal centre and an acidic promoting group, to provide a high activity of the system even without any acid promoter.

Proton Conduction and Long-Range Ferrimagnetic Ordering in Two Isostructural Copper(II) Mesoxalate Metal–Organic Frameworks

Two compounds of formula {(H3O)[Cu7(Hmesox)5(H2O)7]·9H2O}n (1a) and {(NH4)0.6(H3O)0.4[Cu7(Hmesox)5(H2O)7]·11H2O}n (1b) were prepared and structurally characterized by single-crystal X-ray diffraction (H4mesox = mesoxalic acid, 2-dihydroxymalonic acid). The compounds are crystalline functional metal-organic frameworks exhibiting proton conduction and magnetic ordering. Variable-temperature magnetic susceptibility measurements reveal that the copper(II) ions are strongly ferro- and antiferromagnetically coupled by the alkoxide and carboxylate bridges of the mesoxalate linker to yield long-range magnetic ordering with a Tc of 17.6 K, which is reached by a rare mechanism known as topologic ferrimagnetism. Electric conductivity, measured by impedance methods, shows values as high as 6.5 × 10(-5) S cm(-1) and occurs by proton exchange among the hydronium/ammonium and water molecules of crystallization, which fill the voids left by the three-dimensional copper(II) mesoxalate anionic network.

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.

Two-dimensional (6,3) networks obtained with the {Cu3(Hmesox)3}3− secondary building unit (H4mesox = mesoxalic acid)

The compounds [La(H2O)3Cu3(Hmesox)3(H2O)5]·8H2O (1) and [La(H2O)2Cu3(Hmesox)3(H2O)3]·7H2O (2) have been prepared by the reaction of mesoxalic acid with basic copper(II) carbonate and lanthanum nitrate (H4mesox = mesoxalic acid, dihydroxymalonic acid). The compounds have been characterized by single crystal X-ray diffraction, magnetic susceptibility measurements and DFT calculations. The structure of both compounds is built up by [Cu3(Hmesox)3(H2O)5]3− and [Cu3(Hmesox)3(H2O)3]3− trinuclear entities (for 1 and 2, respectively) linked to La(III) ions to yield 2D sheets with the (6,3) topology if the lanthanum atom and the Cu3 centroids are considered as nodes. Due to the diamagnetic character of the La(III) ion the magnetic behaviour of both compounds is related to the copper(II) trinuclear entities, which display antiferromagnetic coupling making one of the S = 1/2 spin states to be the spin ground state. The magnetic coupling constants of the trinuclear units are determined by means of magnetic susceptibility measurements and they exhibit the expected trend showing strong antiferromagnetic couplings for large Cu–O–Cu bridging angles. Additionally, DFT calculations performed on these complexes agree with the experimental values obtained.

Mesoxalate as Cu(II)–Ln(III) linker in the construction of MOFs in DMSO/water medium

Five new heterometallic 3d–4f metal–organic frameworks with the general formula [Ln(H2O)zCu3(Hmesox)3DMSO]·xH2O·yDMSO (Ln(III) = La, Ce, Pr, Nd and Eu; H4mesox = mesoxalic or dihydroxymalonic acid; and DMSO = dimethylsulfoxide) have been prepared by crystal growth in agarose gel in a mixed solvent (DMSO/water) medium. LaCu3, CeCu3, PrCu3 and NdCu3 yield prismatic well-formed chiral crystals, whereas EuCu3 produces laminar and badly-shaped crystals. The structural analysis shows cubic neutral chiral (10,3)-a networks for the former four compounds. On the other hand, EuCu3 yields neutral chains with lower connectivity, crystallizing in a monoclinic space group. The magnetic susceptibility study reveals antiferromagnetic coupling among the copper(II) ions through the mesoxalate-alkoxo exchange pathway. Theoretical DFT studies agree with the magnetic susceptibility investigations and show a correlation between the intensity of the magnetic coupling and the bridging Cu–O–Cu angles.