Bartłomiej Gaweł

Sol-Gel Synthesis of Non-Silica Monolithic Materials

Monolithic materials have become very popular because of various applications, especially within chromatography and catalysis. Large surface areas and multimodal porosities are great advantages for these applications. New sol-gel preparation methods utilizing phase separation or nanocasting have opened the possibility for preparing materials of other oxides than silica. In this review, we present different synthesis methods for inorganic, non-silica monolithic materials. Some examples of application of the materials are also included.

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.

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).

Unusual Thermal Decomposition of AgIISO4 Yielding AgI2S2O7: Bending Hammond’s Rule

“It could be said that among the coinage metals (Cu, Ag, Au), only silver is normal . (...) gold is anomalous due to large relativistic effects. Copper is anomalous as it has a nodeless and therefore very compact d shell, with strong electron–electron repulsion (...)”. The “normality” of elemental silver, is reflected in the prevalence of its monovalent oxidation state, +1 (as expected for a Group 11 element), which also has severe consequences for its second oxidation state—it renders Ag an extremely powerful oxidizer. The standard redox potential for the Ag/Ag redox pair equals +1.98 V versus NHE and it is surpassed only by those of FC/F , F2/2F , ClC/Cl and OHC/OH . Thus Ag is stabilized in connections with fluoride ligands, whereas its oxo and aza compounds are rare and are quite unstable thermodynamically and thermally. Here we investigate in detail the thermal decomposition of recently synthesized Ag sulfate, AgSO4. [4] The activation energy for decomposition turns out to be substantial ( 127 kJmol ) rendering this compound metastable at ambient (p, T) conditions. We show, based on literature about thermal decomposition for over 50 different sulfates and oxo-sulfates (see the Supporting Information), that solely AgSO4 s low-temperature thermal decomposition is associated with the reduction of a metal cation (“reductive decomposition”). We consider the reaction pathway for decomposition and we point out structural links between AgSO4 and crystalline product of its decomposition, AgSO3.5 Ag2S2O7. Ag sulfate was reported to decompose thermally in a single step while yielding Ag disulfate and releasing O2 [Eq. (1)]:

Exploration of a new building block for the construction of cyano-bridged solvatomagnetic assemblies: [Ni(cyclam)]3+

Two 1D CN-bridged coordination polymers based on the cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) complex of nickel in an unusual oxidation state III have been characterised in terms of structure and solvatomagnetic properties. The {[Ni(cyclam)][Cr(CN)6]·6H2O}n (1) and {[Ni(cyclam)][Fe(CN)6]·6H2O}n (2) chains are isostructural and crystallise in space group C2/m. They undergo reversible partial dehydration at 40 °C to {[Ni(cyclam)][Cr(CN)6]·3H2O}n (1d) and {[Ni(cyclam)][Fe(CN)6]·3H2O}n (2d), accompanied by marked changes in structure and magnetic properties. Strong ferromagnetic exchange interaction J along the chains, together with a much weaker inter-chain interaction, leads to magnetic ordering in the range from 2.4 to 5.8 K. Dehydration of 1 leads to a decrease in J from 32 to 18 K, while dehydration of 2 leads to an increase in J from 6.8 to 14.3 K (interaction Hamiltonian −2JSNiSM). The magnetic susceptibility for the CrIII–NiIII 3/2–1/2 spin alternating Heisenberg chain was analysed with the help of quantum Monte Carlo simulations, simultaneously including both intra- and inter-chain interactions for a bunch of chains. The compounds are the first bimetallic CN-bridged assemblies containing a magnetically coupled octahedral cationic building block of an LS d7 configuration.

Ethylenediamine as a bridging ligand: structure solution of two cadmium(II)-based coordination polymers from powder diffraction data

Structures of [Cd(C 2 H 8 N 2 )Cl 2 ] n (1) and [Cd(C 2 H 8 N 2 )Br 2 ] n (2) were solved from powder diffraction data. Compound (1) crystallizes in the space group Pbam (No. 55), a xa0=xa09.9021(7)xa0A, b xa0=xa07.8186(6)xa0A, c xa0=xa04.0705(3)xa0A, V xa0=xa0315.13(3)xa0A 3 , Z xa0=xa02. (2) is isostructural: space group Pbam (No. 55), a xa0=xa010.405(2)xa0A, b xa0=xa07.8634(8)xa0A, c xa0=xa04.2079(5)xa0A, V xa0=xa0344.28(6)xa0A 3 , Z xa0=xa02. The investigated compounds are examples of two-dimensional hybrid coordination polymers, in which neighboring metal centers are bridged via both organic and inorganic moieties: ethylenediamine molecules and halide anions. Both crystal structures were solved ab initio from powder data using direct methods.

Octamolybdates – promising materials for industry and medicine

desirable to attach organic functionalities covalently to the surface of polyoxoanions. As part of a broad program centered on the functionalization of polyoxometalates, we have been interested in the derivatisation of Lindqvist type polyoxoanions with organosilyl moieties. The condensed polyoxometalate (nBu4N)4[(TaW5O18)2O] which is synthesized by reacting [TaW5O19] with BuSnCl3, crystallises in the orthorhombic system, space group Pbnb with lattice parameters a = 15.7981(14), b = 17.939(3), c = 35.216(6)Å, V= 9980 Å and Z = 4. The crystallographic study of(nBu4N)4[(TaW5O18)2O] shows that the dimer is composed from two polyoxoanions fragments linked by linear Ta-O-Ta bridge. Such a linkage readily reacts with organosilyl (Lewis electrophilic reagents), such as RR’ 2SiOH (R = R’ = Et, iPr, OtBu, Ph; R = tBu, R’ = Me) to yield monomeric plenary Lindqvist derivatives (nBu4N)2[W5O18Ta(O)SiR’R2]. These derivatives are characterized in the solid state by IR and in solution by multinuclear NMR (C, Si, W). The crystallographic study of (nBu4N)2[(W5O18Ta(O)SiPh3)]indicates that {SiPh3} is grafted on the surface of the polyanion through the terminal Ot-Ta oxygen atom.