Marcin Oszajca

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/

Fine refinement of solid state structure of racemic form of phospho-tyrosine employing NMR Crystallography approach

We present step by step facets important in NMR Crystallography strategy employing O-phospho-dl-tyrosine as model sample. The significance of three major techniques being components of this approach: solid state NMR (SS NMR), X-ray diffraction of powdered sample (PXRD) and theoretical calculations (Gauge Invariant Projector Augmented Wave; GIPAW) is discussed. Each experimental technique provides different set of structural constraints. From the PXRD measurement the size of the unit cell, space group and roughly refined molecular structure are established. SS NMR provides information about content of crystallographic asymmetric unit, local geometry, molecular motion in the crystal lattice and hydrogen bonding pattern. GIPAW calculations are employed for validation of quality of elucidation and fine refinement of structure. Crystal and molecular structure of O-phospho-dl-tyrosine solved by NMR Crystallography is deposited at Cambridge Crystallographic Data Center under number CCDC 1005924.

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

Crystalline bilayers unzipped and rezipped: solid-state reaction cycle of a metal–organic framework with triple rearrangement of intralayer bonds

We present a series of remarkable structural transformations for a family of layered metal–organic frameworks (MOFs) in a three-step solid-state reaction cycle. The cycle represents new dynamic behavior of 2D coordination polymers and involves the sequence of reactions: {[Mn2(ina)4(H2O)2]·2EtOH}n (JUK-1) → {(NH4)2[Mn(ina)2(NCS)2]}n·xH2O (JUK-2) → {[Mn2(ina)2(Hina)2(NCS)2]}n (JUK-3) → JUK-1 (Hina = isonicotinic acid), each accompanied by rearrangement of intralayer coordination bonds and each induced by a different external stimulus. In situ investigation of the first step of the cycle by combined synchrotron X-ray diffraction and Raman spectroscopy reveals direct mechanochemical unzipping of JUK-1 bilayers to respective JUK-2 layers with reaction rates dependent on the milling conditions. In contrast, the reverse zipping of JUK-2 layers involves two steps and proceeds through a new MOF (JUK-3) whose structure was elucidated by powder X-ray diffraction. Magnetic measurements confirm conversions of manganese nodes in the reaction cycle. The findings indicate the possibility of developing coordination-based assemblies with large structural responses for use in smart stimuli-responsive systems and sensor technologies.

Synthesis and the crystal structure of dimeric 1-hydroxyhexane-2,3-dione and the spectral characteristics of a model acireductone

An efficient synthetic route to 1-hydroxyhexane-2,3-dione, which is a tautomeric form of a model acireductone, is presented here. Interestingly, the compound was found to crystallise as a stable dimer, a molecule of which contains a 1,3-dioxolane ring. The dimer structure was solved using the PXRD (powder X-ray diffraction) method and confirmed by NMR, IR, and Raman spectroscopy and DFT calculations. The title compound dissolves in water with the formation of several monomeric forms of the model acireductone as revealed by UV-Vis and NMR spectra. The extinction coefficients of the neutral and anionic forms of the monomer were also determined.

Bis(4-methylanilinium) and bis(4-iodoanilinium) pentamolybdates from laboratory X-ray powder data and total energy minimization

The crystal structures of poly[bis(4-methylanilinium) [tetra-μ3-oxido-hexa-μ2-oxido-hexaoxidopentamolybdenum(VI)]], {(C7H10N)2[Mo5O16]}n, (I), and poly[bis(4-iodoanilinium) [tetra-μ3-oxido-hexa-μ2-oxido-hexaoxidopentamolybdenum(VI)]], {(C6H7IN)2[Mo5O16]}n, (II), were determined from laboratory X-ray powder diffraction data using the direct-space parallel-tempering approach and refined by total energy minimization in the solid state. Both compounds adopt layered structures, in which layers of the inorganic {[Mo5O16](2-)}n polyanion alternate with layers of the organoammonium cations parallel to the (100) plane. The asymmetric units contain three Mo atoms (one situated on a twofold axis, Wyckoff position 4e), eight O atoms and one organic cation. Despite the fact that the structure determinations are based on powder diffraction data, due to the total energy minimization approach applied the Mo-O bond lengths can formally be assigned to one of the three groups, reflecting different types of O-atom placement within the polyanion. The cations form relatively strong N-H...O hydrogen bonds, anchoring one end of the organic molecules to both terminal and shared O atoms. The interactions involving the opposite end of the benzene rings are much weaker and include C-H...O and C-H...π bonds in (I) and an I...O halogen bond in (II). Mutual rotation of the benzene rings in both structures leads to the formation of a C-H...H-C dihydrogen bond, with H-atom separations of 1.95 Å in (I) and 2.12 Å in (II). Differential scanning calorimetry measurements show that the interactions between the inorganic and organic layers are stronger in (I) than in (II).

Spectroscopic Evidence for Ligand Substitution Reactions at the Solid–Liquid Interface of a Sub-micrometer Gold(I) Carbene Complex

Colloidal coordination compounds in the sub-micrometer range were synthesized from a chloro gold(I) carbene complex via the anti-solvent procedure and stabilized by a surfactant shell of Tween 20. This compound was successfully applied as model system to monitor heterogeneous multiphase ligand substitution reactions at the solid-liquid interface.

X-ray powder diffraction structural studies of lithol red pigments

Lithol reds belong to the group of azo pigments which were popular artists’ pigments at the beginning of the twentieth century. Under the name lithol red pigment, one can find a family of sodium (PR 49), barium (PR 49:1), calcium (PR 49:2), and strontium (PR 49:3) salts of diazotised Tobias (2-naphthylamine-1-sulphonic) acid coupled with 2-naphthol. The colour of the pigment ranges from yellowish red (sodium salt) to bluish red (strontium salt), depending on the metal cation. The main drawback of lithol red is its very poor lightfastness, which has profound implications for its artistic use (e.g. Mark Rothko’s Seagram and Harvard Murals) [1].

New hybrid materials based on metal sulfates and diamines

In the quest for new functional materials, inorganic frameworks are highly attractive due to their rigidity and stability and their superior electronic, magnetic, and optical properties. Organic building-blocks offer great promises for flexibility, structural diversity, and geometrical control.1 The integration of these two counterparts into a single structure generates hybrid organic– inorganic compounds that play a prominent role in the development of new advanced functional materials. Due to the complementary properties of organic and inorganic components, these materials are suitable for many promising applications in such areas as optoelectronics, environmental protection, or catalysis.2 While it is well known that hybrid compounds can be synthesized as 1dim, 2dim and 3dim assemblies, still a single set of factors determining the dimensionality of the resulting framework has not been identified up to now: literature reports show that temperature, time, pH value, stoichiometry and template identity can have a great influence on the reaction results3. Although many different organic molecule types have been used as templates it is well known that amines and diamines play a prominent role in the synthesis of hybrid compounds.

Polymolybdates and Peroxomolybdates: Candidates for Catalysts in Industry

Progress in catalysis depends on a full understanding of the role of the individual components of catalytic materials. Crystallographic studies offer insight into crystal structure, which enables the rational selection of reagents and better planning of the syntheses of novel materials and catalysts. In this paper we have studied the process of the oxidation of hydrocarbons and terpenes with oxygen from the air. Processes of this type are important in so-called “Green Chemistry.” Their application can reduce the amount of environmentally harmful pollutants formed through conventional oxidation based on nitric acid. While investigating the catalytic activity of peroxoand polymolybdates(VI) in the oxidation of cycloalkanes, we found a number of intriguing relationships. To explain them, we designed, synthesized and solved the crystal structures of the family of new peroxomolybdates, tri-, octaand pentamolybdates of amines. Both single crystal and polycrystalline materials were investigated using laboratory as well as synchrotron radiation. Next, we used these compounds as catalysts in certain interesting for industry processes (e.g. oxidation of cyclic hydrocarbons). We have concluded that: − The activity of peroxocompounds is enhanced by the coordination of N-oxide groups to Mo atoms. − The activity of anionic polymeric trimolybdates decreases when ‘surface of polymeric fiber’ is blocked by cations. − The anionic layers of pentamolybdates are separated by cations of variable size. The distance between layers plays a role similar to that of the size of channels in zeolites. Summary: Peroxomolybdates and polyoxomolybdates show great prospects for new industrial uses (besides cracking and desulfurization).