Mariadel Déniz

Metal-organic coordination frameworks based on mixed methylmalonate and 4,4′-bipiridine ligands: synthesis, crystal structure and magnetic properties

Five new complexes of formulae [M2(4,4′-bpy)(Memal)2X2]n [M = Fe(III) (2), Mn(II) (3), Co(II) (4), Ni(II) (5) and Zn(II) (6), and X = Cl−/OH− (2) and H2O (3–6); 4,4′-bpy = 4,4′-bipyridine and Memal = methylmalonate dianion] have been synthesized by following the previously reported procedure for [Cu2(4,4′-bpy)(Memal)2(H2O)2]n (1). Moreover, two new phases of the Cu(II)/Memal/4,4′-bpy system, namely {[Cu(4,4′-bpy)2][Cu(4,4′-bpy)2(Memal)(NO3)(H2O)]}n·nNO3·3.5nH2O (7) and [Cu(4,4′-bpy)2(Memal)(H2O)]n·nH2O (8), were obtained by varying the synthetic conditions. They were all structurally characterized by single crystal X-ray diffraction, and the magnetic properties of 2–5, 7 and 8 were investigated in the temperature range 1.9–295 K. 1–6 are isomorphous compounds whose structure consists of square grids of metal ions linked through anti–syn carboxylate bridges that grow in the crystallographic ac plane. These layers are pillared along the b axis by bis-monodentate 4,4′-bpy ligands to afford a [4466]-sqp three-dimensional net. Ferro- (1 and 5) and antiferromagnetic (2–4) interactions between the metal ions are mediated by the carboxylate bridge in the anti–syn conformation, the bis-monodentate 4,4′-bpy ligand being unable to transmit a significant magnetic coupling. The values of the magnetic coupling (J) for 2–5 are −0.269(3), −0.225(2), −0.05 and +0.272(3) cm−1 respectively, the isotropic spin Hamiltonian being . Complexes 7 and 8 exhibit quite a different structure, as driven by the 4,4′-bpy groups. A square-grid of [Cu(4,4′-bpy)2]2n+n occurs in 7, which grows in the ab plane and is pillared through anti–syn carboxylate bridges from [Cu(Memal)(4,4′-bpy)2(NO3)(H2O)] units along the c axis to build up a [41263]-pcu net. Analysis of the magnetic data for this compound shows an overall antiferromagnetic behaviour with the coexistence of ferro- and antiferromagnetic interactions. The structure of 8 consists of linear chains of copper(II) running along the c axis, where aquabis(4,4′-bipyridine)copper(II) units are connected by bis(monodentate) methylmalonate ligands. A significant intrachain antiferromagnetic interaction is observed in 8 through the extended Cu–OCCCO–Cu exchange pathway [J = −1.38(1) cm−1]. The assembling role of the 4,4′-bpy coligand in 1–8 and in previous malonate-containing complexes is analyzed and discussed.

Photoluminescent and Slow Magnetic Relaxation Studies on Lanthanide(III)-2,5-pyrazinedicarboxylate Frameworks

In the series described in this work, the hydrothermal synthesis led to oxidation of the 5-methyl-pyrazinecarboxylate anion to the 2,5-pyrazinedicarboxylate dianion (2,5-pzdc) allowing the preparation of three-dimensional (3D) lanthanide(III) organic frameworks of formula {[Ln2(2,5-pzdc)3(H2O)4]·6H2O}n [Ln = Ce (1), Pr (2), Nd (3), and Eu (4)] and {[Er2(2,5-pzdc)3(H2O)4]·5H2O}n (5). Single-crystal X-ray diffraction on 1-5 reveals that they crystallize in the triclinic system, P1̅ space group with the series 1-4 being isostructural. The crystal structure of the five compounds are 3D with the lanthanide(III) ions linked through 2,5-pzdc2- dianions acting as two- and fourfold connectors, building a binodal 4,4-connected (4·648)(426282)-mog network. The photophysical properties of the Nd(III) (3) and Eu(III) (4) complexes exhibit sensitized photoluminescence in the near-infrared and visible regions, respectively. The photoluminescence intensity and lifetime of 4 were very sensitive due to the luminescence quenching of the 5D0 level by O-H oscillators of four water molecules in the first coordination sphere leading to a quantum efficiency of 11%. Variable-temperature magnetic susceptibility measurements for 1-5 reveal behaviors as expected for the ground terms of the magnetically isolated rare-earth ions [2F5/2, 2H4, 4I9/2, 7F0, and 4I15/2 for Ce(III), Pr(III), Nd(III), Eu(III), and Er(III), respectively] with MJ = 0 (2 and 4) and ±1/2 (1, 3, and 5). Q-band electron paramagnetic resonance measurements at low temperature corroborate these facts. Frequency-dependent alternating-current magnetic susceptibility signals under external direct-current fields in the range of 100-2500 G were observed for the Kramers ions of 1, 3, and 5, indicating slow magnetic relaxation (single-ion magnet) behavior. In these compounds, τ-1 decreases with decreasing temperature at any magnetic field, but no Arrhenius law can simulate such a dependence in all the temperature range. This dependence can be reproduced by the contributions of direct and Raman processes, the Raman exponent (n) reaching the expected value (n = 9) for a Kramers system.

Syntheses, crystal structures and magnetic properties of five new manganese(ii) complexes: Influence of the conformation of different alkyl/aryl substituted malonate ligands on the crystal packing

Five new manganese(II)-based complexes of general formula [Mn(Rmal)(H2O)]n with Rmal = methylmalonate (Memal) (1), dimethylmalonate (Me2mal) (2), diethylmalonate (Et2mal) (3), butylmalonate (Butmal) (4) and benzylmalonate (Bzmal) (5) were synthesized and their structures characterized by single crystal X-ray diffraction. 1 and 2 are three-dimensional compounds whereas 3–5 exhibit two-dimensional networks. The structure of 1 consists of chains of μ-κO:κO bridged aquamanganese(II) ions which are interlinked through anti–anti carboxylate bridges. The structure of 2 is built by double μ-κO:κO bridged bis[aquamanganese(II)] entities which are linked to six other dimanganese(II) units through oxo- and anti–syn carboxylate bridges. These dinuclear entities also occur in 4 and 5. They are interconnected by anti–anti and anti–syn carboxylate bridges to four other units, leading to neutral layered structures. Finally, compound 3 consists of aqua-bridged chains of manganese(II) ions connected through tetrakis(monodentate) Et2mal ligands leading to a sheet-like structure. The topological representation of the crystal structures shows the of four different nets: (10,3)-d utp (1), 6-connected crs (2), gek2 (3) and the square-grid sql topology (4–5). The magnetic properties of 1–5 were investigated in the temperature range 2.0–300 K. Overall antiferromagnetic behavior occurs in 1, 2, 4 and 5 with susceptibility maxima in the range 3.6–17.0 K. Compound 3 exhibits an overall antiferromagnetic behaviour in the high temperature range with a weak spin canting in the low temperature domain and magnetic ordering below ca. 32 K.

Solution and solid state studies with the bis-oxalato building block [Cr(pyim)(C2O4)2]− [pyim = 2-(2′-pyridyl)imidazole]

The preparation, X-ray structure, and variable temperature magnetic study of the new compound {Ba(H2O)3/2[Cr(pyim)(C2O4)2]2}n·9/2nH2O (1) [pyim = 2-(2′-pyridyl)imidazole and C2O42− = dianion of oxalic acid], together with the potentiometric and spectrophotometric studies of the protonation/deprotonation equilibria of the pyim ligand and the ternary complex [Cr(pyim)(C2O4)2]−, are reported herein. The crystal structure of 1 consists of neutral chains, with diamond-shaped units sharing barium(II), with the two other corners occupied by chromium(III). The two metal centers are connected through bis(bidentate) oxalate. Very weak antiferromagnetic interactions between the chromium(III) ions occur in 1. The values of the protonation constants of the imidazole and pyridyl fragments of pyim as well as the acidity constant of the coordinated pyim in [Cr(pyim)(C2O4)2]− are determined for the first time by potentiometry and UV–Vis spectroscopy in aqueous solution (25 °C and 0.15 M NaNO3 as ionic strength).

Influence of the coligand in the magnetic properties of a series of copper(II)–phenylmalonate complexes

This work presents a series of layered systems based on phenylmalonate-containing copper(II) complexes and different coligands. Eight compounds [Cu(L)(Phmal)]n where L = pyrimidine (pym, 1) pyrazine (pyz, 2), 3-cyanopyridine (3-CNpy, 3), 4-cyanopyridine (4-CNpy, 4), 3-fluoropyridine (3-Fpy, 5), 3-chloropyridine (3-Clpy, 6), 3-bromopyridine (3-Brpy, 7) and 3-iodopyridine (3-Ipy, 8), have been synthesized and magneto-structurally characterized. The coligands selected not only modify the coordination environment of the metal ion, blocking or extending the polymerization, but also interact with the phenyl ring of the phenylmalonate ligand and dramatically affect the crystal packing through weak interactions. The crystallographic analysis reveals that compounds 1–8 present a corrugated square grid of carboxylate bridged copper(II) atoms where the pyridine ligands are alternatively located above and below each layer and, at the same time, inversely to the position of the phenyl group of the Phmal ligand. It is important to note that the pym and pyz ligands in 1 and 2 do not act as bridges between two copper atoms, whereas weak interactions between the cyano groups are also present in the structures of the complexes 3 and 4. The increase of the Van der Waals radius of the halogen along the series 5–8 accounts for the increase of the interlayer separation. Variable-temperature magnetic susceptibility measurements show the occurrence of different magnetic behaviours. Weak interactions are expected for the anti–syn carboxylate bridge in the out-of-plane configuration, that can be either ferro- or antiferromagnetic. Therefore, in this manuscript we shed light on the influence of the magneto-structural relationship in these square grid layered Cu(II) complexes.

Three new europium(III) methanetriacetate metal‐organic frameworks: the influence of synthesis on the product topology

Three new metal-organic framework structures containing Eu(III) and the little explored methanetriacetate (C7H7O6(3-), mta(3-)) ligand have been synthesized. Gel synthesis yields a two-dimensional framework with the formula [Eu(mta)(H2O)3]n·2nH2O, (I), while two polymorphs of the three-dimensional framework material [Eu(mta)(H2O)]n·nH2O, (II) and (III), are obtained through hydrothermal synthesis at either 423 or 443 K. Compounds (I) and (II) are isomorphous with previously reported Gd(III) compounds, but compound (III) constitutes a new phase. Compound (I) can be described in terms of dinuclear [Eu2(H2O)4](6+) units bonded through mta(3-) ligands to form a two-dimensional framework with topology corresponding to a (6,3)-connected binodal (4(3))(4(6)6(6)8(3))-kgd net, where the dinuclear [Eu2(H2O)4](6+) units are considered as a single node. Compounds (II) and (III) have distinct three-dimensional topologies, namely a (4(12)6(3))(4(9)6(6))-nia net for (II) and a (4(10)6(5))(4(11)6(4))-K2O2; 36641 net for (III). The crystal density of (III) is greater than that of (II), consistent with the increase of temperature, and thereby autogeneous pressure, in the hydrothermal synthesis.

Cadmium(II) coordination polymers based on substituted malonic acid: synthesis, characterization and photoluminescence properties

Four novel complexes of cadmium(II) with alkyl/aryl-substituted malonate ligands of formulae {[Cd(Memal)(H2O)]6·0.5H2O}n (1), [Cd(Etmal)(H2O)]n (2), [Cd(Butmal)(H2O)]n (3) and [Cd(Bzmal)(H2O)]n (4), (Memal = methylmalonate, Etmal = ethylmalonate, Butmal = butylmalonate and Bzmal = benzylmalonate) have been prepared and characterized by single crystal X-ray analysis. Their luminescence, UV-Vis absorption properties and thermal behaviour were also investigated. Complex 1 is a three-dimensional compound where each metal centre is connected to four other ones leading to a sodalite network with the point symbol {42·64}. Each cadmium(II) ion in 1 is seven-coordinate with a water molecule and six oxygen atoms from three Memal ligands building a somewhat distorted pentagonal bipyramidal surrounding. The Memal ligand in 1 adopts a μ3–κO:κ2O′:κ2O′′:κO′′′ coordination mode. 2–4 are isomorphous compounds with a two-dimensional structure where centrosymmetric double oxo(carboxylate-substituted malonate)-bridged dicadmium(II) units are linked to four other dinuclear entities through anti–anti and anti–syn carboxylate bridges to form a Shubnikov tetragonal layered [4462]-sql net. Each cadmium(II) ion in 2–4 is six-coordinate in a distorted octahedral environment with four carboxylate-oxygen atoms building the basal plane and a water molecule plus another carboxylate-oxygen atom in the axial positions. The substituted malonate ligands in 2–4 exhibit the μ4–κO:κ2O′:κ2O′′:κO′′′ coordination mode. The tests of the emission spectra of 1–4 show that the length of the side chain influences the photoluminescence properties of the complexes. Finally, the decays of the luminescence of 1–4 and the respective free substituted malonic acids reveal that the same value of the average life time is observed for 1 (H2Memal), whereas in the case of 2–4, they are greater than that of 1 and those of their corresponding acids. The longer decay rates in 2–4 are consistent with the lack of water molecules in the environment of the cadmium(II) ion in these complexes, indicating that the sheet-like structure of 2–4 provides a chemical surrounding with less non-radiative relaxation processes.

Dynamic behavior in a dryness sensitive 3d-4fmetal–organic framework

Dynamic behavior in a dryness sensitive 3d-4f metal–organic framework Oscar Fabelo,a,b,c Pau Díaz-Gallifa,c Laura Cañadillas-Delgado,a,b,c Jorge Pasán,c Carla Martinez-Benito,c Mariadel Déniz,c Diego Lozano,c Ana Labrador,d Catalina Ruiz-Pérez,c aInstituto de Ciencia de Materiales de Aragón. CSIC-Universidad de Zaragoza. (Spain). bInstitute Laue Langevin. Grenoble (France). cLaboratorio de Rayos X y Materiales Moleculares, Depto. Física Fundamental II, Universidad de La Laguna. Tenerife. (Spain). dBM16 – LLS. European Synchrotron Radiation Facility. Grenoble (France). E-mail: fabelo@ill.fr