Wiesław Łasocha

Double Switching of a Magnetic Coordination Framework through Intraskeletal Molecular Rearrangement

Molecular systems which undergo reversible structural transformations on application of external stimuli and show additional strongly intertwined physical phenomena are fundamental to the generation of nanoscale multifunctional molecular devices. Multifunctional molecular systems are recognized as potentially revolutionary magnetic, electric, and magneto-optical materials with possible applications in data storage/processing at the molecular level, as molecular switching devices in gas processing systems, and molecular sensors. In the field of porous molecular magnetic materials, the structural versatility of coordination chemistry has allowed the engineering of materials having novel topologies and remarkable properties. Magnetic coordination compounds with high magnetic ordering temperatures Tc exceeding the boiling point of liquid nitrogen are achievable in cyanidoor tetracyanoethylenebridged molecular solids. Incorporation of relatively large organic molecules into the structures of the former led to hybrid systems showing multifunctionality but usually with significantly lower Tc due to the lower ratio of bridging/ terminal CN ligands. Controlled dehydration of selected cyanido-bridged hybrids may result in substantial increase of Tc due to structural transformations involving terminal CN groups. However, there have been practically no reports on rational utilization of the terminal CN ligands and large organic molecules incorporated into the molecular framework to impart multifunctionality on these materials. Recently, we recognized the great potential of terminal CN groups and successfully exploited it in an Mn-imidazole– [Nb(CN)8] magnetic spongelike material to reversibly increase its critical temperature from 25 to 62 K. Here we present a cyanido-bridged molecular magnet in which the coordinated organic molecules and terminal CN ligands are appropriately arranged to provide a unique coexistence of molecule-specific porosity and doubly switchable high ordering temperature in one material. Orange platelike crystals of {[Mn(pydz)(H2O)2][Mn (H2O)2][Nb (CN)8]·2H2O}n (1; pydz = pyridazine, C4H4N2) were crystallized from an aqueous solution of MnCl2·4 H2O, pyridazine, and K4[Nb(CN)8]·2H2O (for details, see Supporting Information). Samples of 1 can be stored in a closed vessel for several months without decomposition. The structure of 1 was determined by single-crystal X-ray diffraction analysis (space group P21/c ; for details, see Supporting Information and CCDC 810685). The cyanido-bridged Mn2Nb skeleton of 1 (Figure 1a) consists of Mn2-NC-Nb square-grid motifs (in the bc plane) cross-linked at Nb centers by Mn1-NC-Nb ladders (along the a axis). Both Mn1 and Mn2 centers in 1 are octahedral (coordination number cn = 6), but their coordination spheres are different (Figure S2, top in the Supporting Information). Mn1 is coordinated by three nitrogen atoms of CN ligands (mer), one nitrogen atom of pyridazine (N11), and two aqua ligands in trans geometry. Mn1 belongs exclusively to the ladder motifs. The coordination sphere of Mn2, on the contrary, is purely inorganic and comprises four cyanido ligands in the equatorial plane and two aqua ligands in trans geometry. Mn2 belongs to the square-grid motifs. The only terminal CN ligand of the [Nb(CN)8] moiety (C4N4) is involved in a strong hydrogen bond with oxygen atom O11 of the aqua ligand coordinated to Mn1 (N4 Mn1 4.37 ). The noncoordinating nitrogen atom of the pyridazine ligand (N16) is involved in a hydrogen-bond to the aqua ligand (O22) of Mn2 (N16 Mn2 4.19 ; Figure 1a, bottom and Figure S3a in the Supporting Information). The local hydrogen-bonding system is completed by the H2O molecule of crystallization (O2) bound to O22 and N4. Such an arrangement is very promising from the point of view of topotactic reactivity of the terminal CN and pyridazine ligands. [*] Dr. D. Pinkowicz, Dr. R. Podgajny, Dr. B. Gaweł, Dr. W. Nitek, Prof. Dr. W. Łasocha, M. Oszajca, Prof. Dr. B. Sieklucka Faculty of Chemistry Jagiellonian University Ingardena 3, 30-060 Krak w (Poland) Fax: (+ 48)12-634-0515 E-mail: pinkowic@chemia.uj.edu.pl barbara.sieklucka@uj.edu.pl Homepage: http://www.chemia.uj.edu.pl/znmm/

Magnetic Spongelike Behavior of 3D Ferrimagnetic {[MnII(imH)]2[NbIV(CN)8]}n with Tc = 62 K

Fully reversible room temperature dehydration of 3D {Mn(II)2(imH)2(H2O)4[Nb(IV)(CN)8] x 4 H2O}n (1; imH = imidazole) of Tc = 25 K results in the formation of 3D ferrimagnet {[Mn(II)(imH)]2[Nb(IV)(CN)8]}n (2), with Tc = 62 K, the highest ever known for octacyanometalate-based compounds. The dramatic magnetostructural modifications in 2 provide the first example of magnetic spongelike behavior in an octacyanometallate-based assembly.

Towards high Tc octacyanometalate-based networks

We present an overview of very recent advances in the engineering of magnetic networks based on octacyanometalates. The selected magnetic networks of CuIIWV, NiIIWV and MnIILNbIV (L – organic bridging linker) illustrate the possible strategies for tuning of the magnetic characteristics. The combination of magnetic ordering for 2D (two-dimensional) and 3D (three-dimensional) networks together with the solvent sensitivity of a cyano-bridged framework resulted in the development of a novel 3D {[MnII(imH)]2[NbIV(CN)8]} assembly with magnetic sponge character, characterized by Tc of 62 K, the highest ever observed for octacyanometalate-based networks.

Exploring the formation of 3D ferromagnetic cyano-bridged CuII2+x{CuII4[WV(CN)8]4−2x[WIV(CN)8]2x}·yH2O networks

Two novel non-stoichiometric 3D cyano-bridged coordination networks of general formula CuII2+x{CuII4[WV(CN)8]4−2x[WIV(CN)8]2x}·yH2O were obtained according to two different synthetic strategies. The heterogeneous reaction between solid 2D cyano-bridged network (dienH3){CuII[WV(CN)8]}3·4H2O (1) (dienH33+ = protonated diethylenetriamine) and an aqueous solution of DyIII(NO3)3 results in the removal of dienH33+ cations and the formation of a 3D cyano-bridged CuII2.44{CuII4[WV(CN)8]3.12[WIV(CN)8]0.88}·5H2O (2) network. The direct combination of [CuII(H2O)6]2+ and [WV(CN)8]3− in aqueous media leads to the structurally related CuII2.97{CuII4[WV(CN)8]2.06[WIV(CN)8]1.94}·4H2O (3) assembly. The assemblies 2 and 3 were characterised by X-ray powder diffraction along with IR, X-ray absorption spectroscopy (XAS), proton induced X-ray emission (PIXE) and magnetic measurements. 2 and 3 crystallise in a tetragonal system, space group I4/mmm with cell parameters a = b = 7.2695(9) A; c = 28.268(5) A; Z = 2 (2) and a = b = 7.2858(9) A, c = 28.282(5) A, Z = 2 (3). Both networks are characterised by the increase of TC from 33 K to 40 K and coercivity from 0.2 to 2–2.5 kOe compared to 1. Despite their general structural and magnetic similarity, 2 and 3 reveal significant differences in magnetic dimensionality: compound 2 exhibits the features of a metamagnet with a threshold field of 1.8 kOe at 4.2 K, while compound 3 resembles a classical magnet with 3D ordering. This difference is discussed in terms of non-stoichiometry of the networks accompanied by the appearance of different numbers of non-magnetic “defects” due to the formation of diamagnetic W(IV) centres.

Release of boron during conversion of MFI boralite to ammonium and hydrogen forms

Conversion of synthetic boralites with the MFI struture to ammonium and hydrogen forms is accompanied by release of skeletal boron — up to 50% of initial content — without changes in the crystallinity (determined by XRD). The deboronation level β of the hydrogen form is greater than that of the ammonium variety, and for both types it increases with increasing B/u.c., i.e., with decreasing SiO2/B2O3 molar ratio. As a result of hydrolysis, ammonolysis, and dehydroxylation reactions, boron vacancies occur that loosen the structure and cause the u.c. volume of the hydrogen forms to be greater than are the corresponding “as-made” boralites. Aluminium impurities (from the synthesis raw materials) are significant for the modified forms with B/u.c. ≤ 0.78 (SiO2/B2O3 ≥ 245) and can generate Bronsted acidity. The boron content (B/u.c.), the deboronation level (β), the content of vacancies per unit cell, and the unit cell content of the modified forms depends on a single synthesis parameter, viz. the SiO2/B2O3 of the reaction mixture.

KAgF3, K2AgF4 and K3Ag2F7: important steps towards a layered antiferromagnetic fluoroargentate(II),

Crystal structure and magnetic properties of K2AgF4, related to recently studied Cs2AgF4, have been scrutinized. It crystallizes orthorhombic (Cmca No.64) with a = 6.182(3) A, b = 12.632(5) A, c = 6.436(3) A (Z = 4, V = 502.6(7) A3). K2AgF4 exhibits slightly puckered [AgF2] sheets and a compressed octahedral coordination of Ag(II) and it is not isostructural to related Cs2AgF4. Violet–coloured K2AgF4 orders ferromagnetically below 26 K. The DFT calculations reproduce semiconducting properties and ferromagnetism of K2AgF4 at the LSDA + U level but only if substantial values of Mott–Hubbard on-site electron–electron repulsion energies for Ag and F are used in calculations. We have also succeeded to solve the crystal structure of a brown KAgF3 (1D antiferromagnet below 64 K; GdFeO3–type, PnmaNo. 62, a = 6.2689(2) A, b = 8.3015(2) A, c = 6.1844(2) A, Z = 4, V = 321.84(2) A3) and to prepare K3Ag2F7, a novel KAgF3/K2AgF4 intergrowth phase and a member of the Ruddlsden–Popper KnAgFn+2 series (n = 1.5). Dark brown K3Ag2F7 crystallizes orthorhombic (K3Cu2Cl7-type, CccaNo. 68, setting 2) with a = 20.8119(14) A, b = 6.3402(4) A, c = 6.2134(4) A (Z = 4, V = 819.87(9) A3).

Crystal structure of potassium and ammonium tetraperoxovanadates (V)

Powder diffraction measurements are fast, and sample preparation does not require time consuming manipulations what is very important for toxic, unstable or explosive samples. In addition, very good results can be also obtained at structure solution level by nowadays methods. Unfortunately, structure solution results can sometimes be biased towards assumed structure models in most popular nowadays ‘direct space search procedures’. However, in typical applications crystal structure studies can be performed using ‘ab initio’ methods. Using this approach the crystal structures of two very unstable tetraperoxovanadates (V) — (NH4)3[V(O2)4] and K3[V(O2)4] — have been ab initio solved from powder diffraction data by direct methods. The two ammonium and potassium salts are isotypic with lattice parameters: a = 6.9769(5), c = 8.211(1) and a = 6.6861(4), c = 7.708(2) Å, V = 399.68(7) Å3 and 344.6(6) Å3, respectively. The space group is I-42m (No. 121) with Z = 2 for both compounds.

Prospective Catalytic Structured Converters for NH3-SCR of NOx from Biogas Stationary Engines: In Situ Template-Free Synthesis of ZSM-5 Cu Exchanged Catalysts on Steel Carriers

The main objective of this study is to develop highly active catalyst and its preparation method that would meet the requirements of steel carriers for short-channel structured converters for NOx abatement from stationary biogas engines. The in situ synthesis was applied to deposit a series of Cu-exchanged MFI zeolite (ZSM-5) on kanthal sheets. The samples differ in preparation conditions: organic template assisted and template-free synthesis, Si/Al ratio and catalyst carrier pretreatment (calcined vs. non-calcined). Dip-coating method was used as a reference to compare loading efficiency. In order to evaluate preparation quality and purity of resulting structure the samples were examined by XRD and SEM/EDS at various stages of preparation. For the assessment of mechanical endurance of the deposited catalyst layers the ultrasonication method was used. The results demonstrated high depositing efficiency of the in situ synthesis as well as high activity and selectivity of the Cu-exchanged MFI samples prepared without costly organic template.

Thermally Induced Changes in the Structure, Composition, and Chemical Properties of LiMn2O4 ±x Spinel Prepared by Sol–Gel Method

Sol–gel method followed by calcination at temperatures of 300–900 °C was used to obtain a series of LiMn2O4 samples with varying amounts of chemical and structural defects while preserving a constant Li:Mn atomic ratio. The physicochemical and structural properties of the samples were characterized by X-ray diffraction (XRD), thermal gravimetry analysis–mass spectrometry (TGA–MS), differential scanning calorimetry (DSC), and Raman spectroscopy techniques. These results were correlated with separately performed high-frequency EMR measurements on the same samples. The oxidation number of Mn ions changes as compared with the stoichiometric spinel composition LiMn2O4. These changes, induced by the removal or incorporation of oxygen, were analyzed and correlated with the appearance or disappearance of the cubic to orthorhombic phase transition at around room temperature. The phase transition occurs only if the concentration of vacancies (cationic or anionic) is below the limit necessary to form sufficient majority of perfect MnO6 octahedra of the high symmetry, Oh7. Disturbance of this high local symmetry, being a condition for Jahn–Teller distortion, seems to also be the decisive factor in suppressing the phase transition that is regarded to be responsible for electrical capacity fading during cell cycling.

Molybdenum Complexes as Catalysts for the Oxidation of Cycloalkanes with Molecular Oxygen

A group of new polymolybdates was synthesized and tested in the catalytic oxidation of cycloalkanes. Investigated compounds exhibit broad structural diversity including polymolybdates with isolated anionic clusters (0-dim), polymeric anions (1-dim), Mo–O layers (2-dim) as well as hexagonal and orthorhombic molybdenum oxides (3-dim). All studied molybdenum complexes were found to be active in the reaction conditions yielding ketones and alcohols as main products. In the case of layered compounds (2-dim), dicarboxylic acid was detected in the mixture of reaction products. The structure of investigated molybdenum compounds was shown to have influence on yields and selectivities of the investigated reactions. Anionic layers separation (in 2-dim materials) as well as type and charge of organic cations present in the compounds are prime examples of structural factors influencing the oxidation reactions efficiencies. On the basis of obtained results and literature reports a mechanism for the oxidation of cycloalkanes by polymolybdates has been proposed.Graphical Abstract