Dariusz Matoga

Coordination versatility of tridentate pyridyl aroylhydrazones towards iron: tracking down the elusive aroylhydrazono-based ferric spin-crossover molecular materials

The two potentially tridentate and monoprotic Schiff bases acetylpyridine benzoylhydrazone (HL(1)) and acetylpyridine 4-tert-butylbenzoylhydrazone (HL(2)) demonstrate remarkable coordination versatility towards iron on account of their propensity to undergo tautomeric transformations as imposed by the metal centre. Each of the pyridyl aroylhydrazone ligands complexes with the ferrous or ferric ion under strictly controlled reaction conditions to afford three six-coordinate mononuclear compounds [Fe(II)(HL)(2)](ClO(4))(2), [Fe(II)L(2)] and [Fe(III)L(2)]ClO(4) (HL = HL(1) or HL(2)) displaying distinct colours congruent with their intense CT visible absorptions. The synthetic manoeuvres rely crucially on the stoichiometry of the reactants, the basicities of the reaction mixtures and the choice of solvent. Electrochemically, each of these iron compounds exhibits a reversible metal-centred redox process. By all appearances, [Fe(III)(L(1))(2)]ClO(4) is one of only two examples of a crystallographically elucidated iron(III) bis-chelate compound of a pyridyl aroylhydrazone. Several pertinent physical measurements have established that each of the Schiff bases stabilises multiple spin states of iron; the enolate form of these ligands exhibits greater field strength than does the corresponding neutral keto tautomer. To the best of our knowledge, [Fe(III)(L(1))(2)]ClO(4) and [Fe(III)(L(2))(2)]ClO(4) are the first examples of ferric spin crossovers of aroylhydrazones. Whereas in the former the spin crossover (SCO) is an intricate gradual process, in the latter the (6)A(1)↔(2)T(2) transition curve is sigmoidal with T(½)∼280 K and the SCO is virtually complete. As regards [Fe(III)(L(1))(2)]ClO(4), Mössbauer and EPR spectroscopic techniques have revealed remarkable dependence of the spin transition on sample type and extent of solvation. In frozen MeOH solution at liquid nitrogen temperature, both iron(III) compounds exist wholly in the doublet ground state.

Molecule-based magnetic materials based on dinuclear ruthenium carboxylate and octacyanotungstate

Two structurally different polymeric complexes consisting of ruthenium(II,III) pivalate ([Ru2(piv)]4+) (Hpiv = pivalic acid) and octacyanotungstate(V) ([W(CN)8]3−) ions, [{Ru2(piv)4}3W(CN)8(H2O)] (1) and (PPh4)2[Ru2(piv)4W(CN)8]·0.5H2O (2), were synthesized. The infrared spectra as well as diffused reflectance spectra confirmed the existence of the ruthenium(II,III) pivalate dimer in 1 and 2. The X-ray crystal structure analysis of 2 showed an alternating arrangement of [Ru2(piv)]4+ and [W(CN)8]3− ions in a one-dimensional chain. The temperature-dependent magnetic susceptibility of 2 showed a ferrimagnetic-like behavior. However, the field dependent magnetization curve at 2 K indicates that this complex has an S = 0 ground state. The X-ray crystal structure analysis of 1 showed a two-dimensional layered structure made up of windmill-shaped 28 membered-rings of alternating arrangement of [Ru2(piv)]4+ and [W(CN)8]3−. The magnetic susceptibility and zero-field-cooled and field-cooled magnetization data of 1 showed that this complex is ferrimagnetic with Tc = 44 K. The field dependence of magnetization exhibited a hysteresis with a coercive field of 5600 Oe at 5 K.

Spacer-dependent structural and physicochemical diversity in copper(II) complexes with salicyloyl hydrazones: a monomer and soluble polymers.

Complexation of copper(II) with a series of heterodonor chelating Schiff bases (LL) of salicylic acid hydrazide and aliphatic or cycloaliphatic ketones affords soluble one-dimensional (1D) metallopolymers containing Schiff bases as bridging ligands. Single-crystal X-ray diffraction results reveal nanometer-sized metallopolymeric wires [Cu(μ-LL)(2)](n) with off-axis linkers and a zigzag geometry. Octahedrally coordinated copper centers, exhibiting a Jahn-Teller distortion, are doubly bridged by two Schiff-base molecules in the μ(2)-η(1),η(2) coordination mode. The use of dibutylketone with long alkyl chains as a component for Schiff base formation leads to a distorted square planar monomeric copper(II) complex [Cu(LL)(2)], as evidenced by its X-ray crystal structure. The compounds are characterized by elemental analyses and IR and UV-vis spectroscopy, as well as magnetic susceptibility and cyclic voltammetry measurements. Electrochemical studies on the complexes reveal an existence of polymeric and monomeric forms in solution and the dependence of Cu(II)/Cu(I) reduction potentials on alkyl groups of salicyloyl hydrazone ligands. Polymeric complexes form conducting films on Pt electrodes upon multicycle potential sweeps.

Preparation and characterisation of [M(CN)4O(pz)]2− complexes (M=Mo or W) and their reactivity towards molecular oxygen

Abstract The synthesis and characterisation of (PPh4)2[M(CN)4O(pz)]·3H2O (M=Mo or W; pz=pyrazine) are presented. The salts are reactive towards molecular oxygen, both in solution and in the solid state, with formation of (PPh4)2[M(CN)4O(O2)]. The X-ray crystal structure of the molybdenum compound confirmed the presence of a peroxo ligand cis to the MO bond; the OO bond distance is 1.41 A. The IR spectra exhibit two absorption bands in the 950–850 cm−1 region assigned to the terminal MO group [917 (Mo) and 933 (W) cm−1] and the peroxo group [893 (Mo) and 871 (W) cm−1]. The possible mechanism of molecular oxygen uptake by pyrazine complexes is discussed.

Crystal structures of mixed-ligand oxocyano complexes of molybdenum(IV) and tungsten(IV) and their reactivity towards molecular oxygen studied by IR spectroscopy

The series of compounds, (PPh4)2[M(CN)4O(L)]·xH2O [M = Mo, W; L = pyrazine (pz), pyridine (py); Ph = phenyl group; x = 0, 2, 3], (PPh4)3[Mo(CN)5O]·7H2O and K(PPh4)2[Mo(CN)5O]·5H2O, which are able to bind molecular oxygen giving peroxo complexes (PPh4)2[M(CN)4O(O2)], have been synthesised. The substrates were characterised by thermogravimetric analysis, vibrational and UV-VIS spectroscopy and the crystal structure determination of (PPh4)2[M(CN)4O(pz)]·3H2O. The latter salts are isomorphous and consist of anions of approximately octahedral geometry, forming a three-dimensional hydrogen-bonded network with channels that enable the penetration of dioxygen. The solid state reactions of all the salts with O2 have been studied by measuring their infrared spectra. The integrated intensities of the O–O, pz or py, MO and CN bands change with time according to pseudo-first-order kinetics. The rate constants kobs range from 0.37 × 10−4 to 1.04 × 10−4 s−1 at 323 K. A detailed study of the function of temperature has been undertaken for (PPh4)2[W(CN)4O(pz)]·3H2O. The activation parameters, ΔH# = 68 ± 13 kJ mol−1 and ΔS# = −117 ± 39 J K−1 mol−1, were determined and an associative mechanism of dioxygen uptake was assumed.

Cobalt(II) and copper(II) supramolecular networks with a 1-iminoisoindoline asymmetric pincer

The first synthesis and characterization of cobalt(II) and copper(II) complexes with an in situ prepared novel asymmetric trinitrogen isoindoline-based pincer type ligand, N-(2-picolyl)isoindoline-1-(2-picolyl)imine (pap), are reported. Single-crystal X-ray structures of the cis-[M(pap)Cl2] (M = Cu, Co) complexes reveal the presence of rare seven-membered chelate rings as well as various coordination geometries and packing modes. The water-soluble complexes were found to react with dicarboxylate ions, terephthalate (ta) and succinate (suc), forming three new compounds {[M(H2O)(pap)]2(μ-ta)}·ta·xH2O (M = Cu and Co) and {[Co(pap)(suc)]·xH2O}n. Their single-crystal X-ray structures are reported and discussed. The rigid ta ions facilitate the formation of binuclear hydrated supramolecular frameworks, whereas the flexible suc linker binds [Co(pap)]2+ moieties into 1D zigzag chains. The chains are non-covalently organized into a supramolecular network. The bulky pincer ligand, responsible for the luminescent properties, was found to be inert in these reactions and to facilitate a unique supramolecular architecture through π–π stacking interactions. The compounds presented in this work may have wider applicability, as molecular building blocks, in the construction of either discrete polynuclear clusters or extended networks with desirable properties.

Water-Stable Metal–Organic Framework with Three Hydrogen-Bond Acceptors: Versatile Theoretical and Experimental Insights into Adsorption Ability and Thermo-Hydrolytic Stability

A new microporous cadmium metal-organic framework was synthesized both mechanochemically and in solution by using a sulfonyl-functionalized dicarboxylate linker and an acylhydrazone colinker. The three-dimensional framework is highly stable upon heating to 300 °C as well as in aqueous solutions at elevated temperatures or acidic conditions. The thermally activated material exhibits steep water vapor uptake at low relative pressures at 298 K and excellent recyclability up to 260 °C as confirmed by both quasi-equilibrated temperature-programmed desorption and adsorption (QE-TPDA) method as well as adsorption isotherm measurements. Reversible isotherms and hysteretic isobars recorded for the desorption-adsorption cycles indicate the maximum uptake of 0.19 g/g (at 298 K, up to p/p0 = 1) or 0.18 g/g (at 1 bar, within 295-375 K range), respectively. The experimental isosteric heat of adsorption (48.9 kJ/mol) indicates noncoordinative interactions of water molecules with the framework. Exchange of the solvent molecules in the as-made material with water, performed in the single-crystal to single-crystal manner, allows direct comparison of both X-ray crystal structures. The single-crystal X-ray diffraction for the water-loaded framework demonstrates the orientation of water clusters in the framework cavities and reveals their strong hydrogen bonding with sulfonyl, acyl, and carboxylate groups of the two linkers. The grand canonical Monte Carlo (GCMC) simulations of H2O adsorption corroborate the experimental findings and reveal preferable locations of guest molecules in the framework voids at various pressures. Additionally, both experimental and GCMC simulation insights into the adsorption of CO2 (at 195 K) on the activated framework are presented.

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.

Thermal and photochemical interaction of octacyanometallates(IV), [M(CN)8]4− (M = Mo or W) in the presence of pyrazine

The interactions between [M(CN)8]4− (M = Mo or W) and pyrazine (pz) in the solid state and in aqueous solutions have been analysed. In strongly acidic solutions {pzH+, [M(CN)8]4−} ion pair formation is observed; the pyrazinium salts (pzH)2(H3O)2[Mo(CN)8]·0.5pz·3H2O and (pzH)2K(H3O)[W(CN)8]·H2O have been isolated. The X-ray crystal structure of the latter, and the spectroscopic properties of both, are described. The [W(CN)8]4− anion is approximately square antiprismatic (D4d), with different H-bond environments around the N atoms. The ligand-field photolysis of [M(CN)8]4− in the presence of pyrazine in neutral and alkaline solution results in the formation of tetracyanooxometallates(IV) in equilibrium with pentacyanooxometallates(IV) through the [M(CN)7(pz)]3− anions as intermediates. The formation of the [M(CN)6(pz)2]2− ion, postulated in the literature to be the final product of the alkaline photolysis, has definitively been excluded.

Bulky substituent and solvent-induced alternative nodes for layered Cd–isophthalate/acylhydrazone frameworks

A series of three cadmium-based two-dimensional (2D) metal–organic frameworks, featuring 4-pyridinecarboxaldehyde isonicotinoyl hydrazone bridging pillars (pcih) and either 5-tert-butyl-substituted or non-substituted isophthalate linkers, have been prepared and characterized. Isophthalates with bulky tert-butyl substituents (tBu-iso2−) form two-dimensional (2D) frameworks with various metal node nuclearities: [Cd(tBu-iso)(pcih)(DMF)]n or [Cd2(tBu-iso)2(pcih)2]n, dependent on synthetic conditions; whereas, in contrast, unsubstituted isophthalates (iso2−) yield only the framework with dinuclear nodes [Cd2(iso)2(pcih)2]n, regardless of the conditions. Diverse nodes of interdigitated layers have a significant influence on the thermal stability and adsorption behavior of the materials.