Thermal Desolvation Research Articles

Desolvation–Solvation-Induced Reversible On–Off Switching of Two Memory Channels in a Cobalt(II) Coordination Polymer: Overlay of Spin Crossover and Structural Phase Transition

Desolvation–Solvation-Induced Reversible On–Off Switching of Two Memory Channels in a Cobalt(II) Coordination Polymer: Overlay of Spin Crossover and Structural Phase Transition

Coupling the Individual Motions of the Machine-like Components of Zirconium(IV) Organic Frameworks

Controlling the internal molecular dynamics in reticular materials is a major challenge for the development of nanotechnological applications. In this issue of Chem, Schurko, Loeb, and co-workers show how the ring motion of the [2]rotaxane-based linker and that of the surrounding triphenylene-based struts influence each other within a series of robust zirconium(IV) organic frameworks.

Secondary Metal Coordination Using a Tetranuclear Complex as Ligand Leading to Hexanuclear Complexes with Enhanced Thermal Barriers for Electron Transfer

Postsynthesis of the paramagnetic square-shaped complex {[(Tp*Me)Fe(μ-CN)2(CN)][Co(dmbpy)2]}2(BPh4)2·6MeCN·H2O [1, Tp*Me = tris(3,4,5-trimethylpyrazole)-borate; dmbpy = 4,4′-dimethyl-2,2′-bipyridin...

Interconversion of lanthanide-organic frameworks based on the anions of 2,5-dihydroxyterephthalic acid as connectors

The reaction of a lanthanide precursor with 2,5-dihydroxyterephthalic acid (H4L) yields different MOFs, having [H2L]2− and [L]4− as anionic spacers, in different synthetic conditions. The interconversion conditions have been established for some of them. The known gadolinium coordination polymer (CP) {[Gd2(H2L)3(DMF)4]·2DMF}n (DMF = N,N-dimethylformamide), 1, was prepared in DMF, either at 90 °C or also at room temperature, if assisted by a base diffusion. NMR monitoring for the synthesis of the analogous yttrium system (DMF, 90 °C) showed that the reaction progress relates with the formation of NHMe2 by DMF decomposition. {[Y2(H2L)3(DMF)4]·2DMF}n, 2, isotypic with 1, was obtained. The new structurally characterized CP {[Gd2(H2L)3(H2O)6]·2H2O}n3, has been prepared by initial thermal (T = 170 °C) desolvation of 1 in vacuo (P = 1·10−3 Torr), followed by a hydrothermal treatment. Interestingly, 3 reverted back to 1 by treatment in DMF at 90 °C. Moreover 3 has been obtained starting from the metal nitrate and H4L in hydrothermal conditions (140 °C; 12 h) in the presence of the stoichiometric amount of NaOH. Long reaction times produced the intermediate formation of a mixture where it was possible to identify the new structurally characterized {[Gd2(H2L)3]·2H2O}n, 4, the known {[Gd2(H2L)2(L)0.5(H2O)3]·4H2O}n, 5 and {[Gd2(H2L)(L)(H2O)5]·2H2O}n, 6, while at higher temperature (160 °C; 24 h) the pure 6 was obtained. The observed transformations of 1 into 6 in H2O involve H4L elimination. On the other hand, it was found that the treatment of 6 in DMF in the presence of H4L leads back to 1. Single Crystal X Ray Diffraction (SCXRD) studies were carried out on the new species 2, 3 and 4.

An acetonitrile-solvated cocrystal of piroxicam and succinic acid with co-existing zwitterionic and non-ionized piroxicam molecules.

This work reports a new acetonitrile (ACN)-solvated cocrystal of piroxicam (PRX) and succinic acid (SA), 2C15H13N3O4S·0.5C4H6O4·C2H3N or PRX:SA:ACN (4:1:2), which adopts the triclinic space group P-1. The outcome of crystallization from ACN solution can be controlled by varying only the PRX:SA ratio, with a higher PRX:SA ratio in solution unexpectedly favouring a lower stoichiometric ratio in the solid product. In the new solvate, zwitterionic (Z) and non-ionized (NI) PRX molecules co-exist in the asymmetric unit. In contrast, the nonsolvated PRX-SA cocrystal contains only NI-type PRX molecules. The ACN molecule entrapped in PRX-SA·ACN does not form any hydrogen bonds with the surrounding molecules. In the solvated cocrystal, Z-type molecules form dimers linked by intermolecular N-H...O hydrogen bonds, whereas every pair of NI-type molecules is linked to SA via N-H...O and O-H...N hydrogen bonds. Thermogravimetry and differential scanning calorimetry suggest that thermal desolvation of the solvate sample occurs at 148 °C, and is followed by recrystallization, presumably of a multicomponent PRX-SA structure. Vibrational spectra (IR and Raman spectroscopy) of PRX-SA·ACN and PRX-SA are also used to demonstrate the ability of spectroscopic techniques to distinguish between NI- and Z-type PRX molecules in the solid state. Hence, vibrational spectroscopy can be used to distinguish the PRX-SA cocrystal and its ACN solvate.

Segmental Mobility Studies of Poly(N-isopropyl acrylamide) Interactions with Gold Nanoparticles and Its Use as a Thermally Driven Trapping System.

Thermal desolvation of poly(N-isopropylacrylamide) (PNIPAM) in the presence of a low concentration of gold nanoparticles incorporates the nanoparticles resulting in suspended aggregates. By covalently incorporating <1% acenaphthylene into the polymerization feed this copolymer is enabled to be used as a model to study the segmental mobility of the PNIPAM backbone in response to gold nanoparticles both below and above the desolvation temperature, showing that there is a physical conformational rearrangement of the soluble polymer at ultralow nanoparticle loadings, indicating low affinity interactions with the nanoparticles. Thermal desolvation is capable of extracting >99.9% of the nanoparticles from their solutions and hence demonstrates that poly(N-isopropylacrylamide) can act as an excellent scrubbing system to remove metallic nanomaterial pollutants from solution.

Impact of Substituent Variation on the Presence of Thermal Spin Crossover in a Series of Mononuclear Iron(III) Schiff Base Complexes with Terminal Pseudohalido Co-ligands.

A series of novel iron(III) complexes of the general formula [Fe(L)X] (where L is a dianion of pentadentate Schiff base ligand N,N'-bis({2-hydroxy-3,5-dimethylphenyl}phenyl)methylidene-1,6-diamino-3-azapentane=H2 L1 for 1 and 2; N,N'-bis({2-hydroxy-3-ethoxyphenyl}methylidene)-1,6-diamino-3-azapentane=H2 L2 for 3 and 3⋅C3 H6 O) and X is terminal pseudohalido ligand (X=N3 for 1, X=NCS for 2, and X=NCSe for 3 and 3⋅C3 H6 O) were synthesized and thoroughly characterized. Magnetic measurements revealed the above room temperature spin crossover for isomorphic complexes 1 and 2 (T1/2 =441 K and T1/2 =435 K, respectively), whereas the solvent-free complex 3 showed a half complete spin crossover (T1/2 =250 K), which was detected by variable temperature crystallography as well. On the other hand, solvated complex 3⋅C3 H6 O exhibited permanent high spin state behaviour and either recrystallization or in situ thermal desolvation converts 3⋅C3 H6 O to solvent-free and spin-crossover-active form 3. Magnetic properties of all the reported complexes were also supported by EPR spectroscopy experiments and in addition, DFT and ab initio calculations were employed for the evaluation of the g-factor and zero field splitting parameters.

Influence of Grafted Block Copolymer Structure on Thermoresponsiveness of Superparamagnetic Core–Shell Nanoparticles

The morphology and topology of thermoresponsive polymers have a strong impact on their responsive properties. Grafting onto spherical particles has been shown to reduce responsiveness and transition temperatures; grafting of block copolymers has shown that switchable or retained wettability of a surface or particle during desolvation of one block can take place. Here, doubly thermoresponsive block copolymers were grafted onto spherical, monodisperse, and superparamagnetic iron oxide nanoparticles to investigate the effect of thermal desolvation on spherical brushes of block copolymers. By inverting the block order, the influence of core proximity on the responsive properties of the individual blocks could be studied as well as their relative influence on the nanoparticle colloidal stability. The inner block was shown to experience a stronger reduction in transition temperature and transition enthalpy compared to the outer block. Still, the outer block also experiences a significant reduction in responsiveness due to the restricted environment in the nanoparticle shell compared to that of the free polymer state. The demonstrated pronounced distance dependence importantly implies the possibility, but also the necessity, to radially tailor polymer hydration transitions for applications such as drug delivery, hyperthermia, and biotechnological separation for which thermally responsive nanoparticles are being developed.

Heteroleptic 1D coordination polymers: 5-Coordinated zinc(II) polymer as an efficient transesterification catalyst

The synthesis of three 1D coordination polymers (CPs), [Zn(TPPZ)(HCCB)]n·DMF·H2O (1) [Cd(TPPZ)(HCCB)]n (2) and [Co(TPPZ)(HCCB)]n (3), based on the N,N,N-chelating κ3-2,3,5,6-tetrakis(2-pyridyl)pyrazine (TPPZ) and polymerizing carboxylate (–COO−) 3-(carboxy-methylamino)-4-chlorobenzoic acid (H3CCB) ligands, using a solvothermal method, have been described. The CPs have been adequately characterized by satisfactory elemental analyses, FT-IR, UV–vis, emission, TGA and PXRD analysis. The structure of 1 has been verified by single crystal X-ray diffraction analysis. The structural data revealed the 5-coordinated heteroleptic polymeric framework is exclusively extended through the H3CCB carboxylate group and strong N,N,N-chelating TPPZ ligand acts as a branch terminating site. Notably, the structure of 1 is comprised of one unit of each H2O and DMF solvent in its crystal lattice. In contrast, 2 and 3 exclude lattice solvents, as suggested by PXRD studies, after thermal desolvation of 1. Furthermore, 1 with 5-coordinated Zn(II) centers exhibited an efficient catalytic performance for transesterification reactions, with remarkable stability and good reusability.

Capturing the structural diversification upon thermal desolvation of a robust metal organic framework via a single-crystal-to-single-crystal transformation

Using a robust 2D metal organic framework, {[Zn(bpaipa)]·DMF·2H2O}n (1), structural diversification due to thermal desolvation is captured via single-crystal-to-single-crystal transformation based on X-ray crystallography, FTIR and TGA.

New Solvates of an Old Drug Compound (Phenobarbital): Structure and Stability

The solvent formation of phenobarbital, an important drug compound with an unusually complex polymorphic behavior, was studied in detail. Monosolvates with acetonitrile, nitromethane, dichloromethane, and 1,4-dioxane were produced and characterized by single-crystal and powder X-ray diffraction, thermoanalytical methods, FT-IR, Raman, and solid-state NMR spectroscopy. Thermal desolvation of these compounds yields mainly mixtures of polymorphs III, II, and I. At a low relative humidity (25 °C) the solvates transform to polymorph III, and at higher relative humidity the monohydrate and the metastable polymorphs IV and VI can be present as additional desolvation products. These results highlight the potential complexity of desolvation reactions and illustrate that a tight control of ambient conditions is a prerequisite for the production of phase-pure raw materials of drug compounds. Transformation in aqueous media results in the monohydrate. Below room temperature, the 1,4-dioxane monosolvate undergoes a reversible single-crystal-to-single-crystal phase transition due to the ordering/disordering of 50% of its solvent molecules. Dipolar-dephasing NMR experiments show that the solvent molecules are relatively mobile. Deuterium NMR spectra reinforce that conclusion for the dioxane solvent molecules. The crystal structure of an elusive 1,4-dioxane hemisolvate was also determined. This study clearly indicates the existence of "transient solvates" of phenobarbital. The formation of unstable phases of this kind must be considered in order to better understand how different solvents affect the crystallization of specific polymorphs.

Solvent-Dependent Stabilization of Metastable Monolayer Polymorphs at the Liquid–Solid Interface

Self-assembly of 1,3,5-tris(4'-biphenyl-4"-carbonitrile)benzene monolayers was studied at the liquid-solid interface by scanning tunneling microscopy. Application of different fatty acid homologues as solvents revealed a solvent-induced polymorphism. Yet, tempering triggered irreversible phase transitions of the initially self-assembled monolayers, thereby indicating their metastability. Interestingly, in either case, the same thermodynamically more stable and more densely packed monolayer polymorph was obtained after thermal treatment, irrespective of the initial structure. Again, the same densely packed structure was obtained in complementary solvent-free experiments conducted under ultrahigh vacuum conditions. Thus, self-assembly of metastable polymorphs at room temperature is explained by adsorption of partially solvated species under kinetic control. The irreversible phase transitions are induced by thermal desolvation, that is, desorption of coadsorbed solvent molecules.

Effect of two sonochemical procedures on achieving to different morphologies of lead(II) coordination polymer nano-structures

Micro and nano-structures of a lead(II) coordination polymer, [Pb2(2-Me-8-Hq)2(MeOH)2]n (1), [2-Me-8-HqH=2-methyl-8-hydroxyquinoline], were synthesized by two sonochemical methods. These new micro and nano-structures were characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. Compound 1 was structurally characterized by single-crystal X-ray diffraction and consists of primary dimeric unit of [Pb2(2-Me-8-Hq)2(MeOH)2]. Self assembly between the dimmeric units of [Pb2(2-Me-8-Hq)2(MeOH)2] from Pb-O bonds results in formation of a one-dimensional lead(II) coordination polymer. The PbII-ion in compound 1 has PbO6N1 coordination sphere with a stereo-chemically ‘active’ electron lone pair on the metals. By a reversible solid-state structural transformation, we successfully prepared [Pb2(2-Me-8-Hq)2]n (2) by thermal desolvation of 1. Thermal stability of compound 1 was studied by thermo gravimetric and differential thermal analyses. In addition nano-structure of PbO was prepared from calcination process of compound 1 at 873K.

Solid- and solution-state structural transformations in flexible lead(ii) supramolecular polymers

Reversible solid-state structural transformations of [Pb2(Q-2-c)2(OAc)2(MeOH)2]n (1) and [Pb2(Q-2-c)2(OAc)2(EtOH)2]n (2) to [Pb2(Q-2-c)2(OAc)2]n (3) have been observed upon thermal desolvation of coordinated MeOH (in 1) and EtOH (in 2) molecules. In addition, irreversible solution-state structural transformations of compounds 1, 2 and 3 to [Pb(Q-2-c)2]n (4) have been observed in H2O. Unlike protic solvents, immersion of 1 and 2 in aprotic solvent results in formation of 3.

Role of halogen bonding in clathrate formation of tetra- and hexasalicylides derived from halogenated salicylic acids

A series of oligomeric lactones, namely tetra- and hexasalicylides 1 and 2, was synthesized from various halogenated salicylic acids by a cyclocondensation reaction using POCl3. The clathrate inclusion properties of the macrocycles for some organic solvents were investigated. X-ray structures of several representative clathrates in this series were determined and the results were used to explain various features of their thermal desolvation. Halogen bonding (in particular C–I⋯OC) was found to play a significant role in the thermal stabilization of these crystalline clathrates.

Solvatomorphism of the Antibacterial Dapsone: X-ray Structures and Thermal Desolvation Kinetics

Three non-isostructural solvates of the antibacterial dapsone (DDS) containing dichloromethane [DDS·0.5(DCM)], 1,4-dioxane [DDS·DXN], and tetrahydrofuran [DDS·THF] were prepared and characterized by X-ray diffraction (XRD) and thermal analysis, the latter including hot stage microscopy (HSM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). In addition, their thermal desolvation was investigated by isothermal kinetic studies which indicated the A2 model as the best fit for desolvation of the DCM and DXN solvates, while the R2 model was indicated for the THF solvate. Activation energies for desolvation of these new species were in the range 141–173 kJ mol–1. Attempts were made to reconcile the kinetic models with the observed HSM desolvation behavior and the modes of solvent inclusion within the solvate crystals determined by XRD (viz. isolated sites for the DCM solvate and channel-type for the others).

Structures and H2 Adsorption Properties of Porous Scandium Metal–Organic Frameworks

Two new three-dimensional Sc(III) metal-organic frameworks {[Sc(3)O(L(1))(3)(H(2)O)(3)]·Cl(0.5)(OH)(0.5)(DMF)(4)(H(2)O)(3)}(∞) (1) (H(2)L(1)=1,4-benzene-dicarboxylic acid) and {[Sc(3)O(L(2))(2)(H(2)O)(3)](OH)(H(2)O)(5)(DMF)}(∞) (2) (H(3)L(2)=1,3,5-tris(4-carboxyphenyl)benzene) have been synthesised and characterised. The structures of both 1 and 2 incorporate the trinuclear trigonal planar [Sc(3)(O)(O(2)CR)(6)] building block featuring three Sc(III) centres joined by a central μ(3)-O(2-) donor. Each Sc(III) centre is further bound by four oxygen donors from four different bridging carboxylate anions, and a molecule of water located trans to the μ(3)-O(2-) donor completes the six coordination at the metal centre. Frameworks 1 and 2 show high thermal stability with retention of crystallinity up to 350 °C. The desolvated materials 1a and 2a, in which the solvent has been removed from the pores but with water or hydroxide remaining coordinated to Sc(III), show BET surface areas based upon N(2) uptake of 634 and 1233 m(2) g(-1), respectively, and pore volumes calculated from the maximum N(2) adsorption of 0.25 cm(3) g(-1) and 0.62 cm(3) g(-1), respectively. At 20 bar and 78 K, the H(2) isotherms for desolvated 1a and 2a confirm 2.48 and 1.99 wt% total H(2) uptake, respectively. The isosteric heats of adsorption were estimated to be 5.25 and 2.59 kJ mol(-1) at zero surface coverage for 1a and 2a, respectively. Treatment of 2 with acetone followed by thermal desolvation in vacuo generated free metal coordination sites in a new material 2b. Framework 2b shows an enhanced BET surface area of 1511 m(2) g(-1) and a pore volume of 0.76 cm(3) g(-1), with improved H(2) uptake capacity and a higher heat of H(2) adsorption. At 20 bar, H(2) capacity increases from 1.99 wt% in 2a to 2.64 wt% for 2b, and the H(2) adsorption enthalpy rises markedly from 2.59 to 6.90 kJ mol(-1).

Flexible Poly(amic acid) Conducting Polymers: Effect of Chemical Composition on Structural, Electrochemical, and Mechanical Properties

A new approach for creating flexible, mechanically strong poly(amic acid) (PAA) hybrid copolymers is described. The reduction of gold salts to gold nanoparticles by PAA coupled with its copolymerization in the presence of various silanes (e.g., N-[3-(trimethoxysilyl)-propyl] aniline (TMOSPA), 3-aminopropyl-trimethoxysilane (APTMOS), dichlorodimethylsilane (DCMS), and tetramethoxysilane (TMOS)) has enabled the design of a series of polymeric films. The resulting poly(amic acid), silane, and gold (PSG) solutions were employed for the fabrication of flexible, ternary polymers with a minimum bend ratio of 3 mm using thermal desolvation and/or wet-phase inversion techniques. By controlling the composition and synthesis conditions, porous PSG films were produced that are flexible or rigid, transparent or opaque, and/or mechanically strong. (1)H NMR, (13)C NMR, and Fourier transform infrared spectroscopy (FTIR) characterization results showed that the carboxylic acid moieties were retained in the PSG copolymer. Thermal stabilities with degradation characteristics of the polymers were determined using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Although structurally and morphologically different from the parent PAA, copolymerization with silanes had significantly improved the mechanical and interfacial property of the PSG class of films.

A bis(amine–carboxylate) copper(II) coordination compound forms a two-dimensional metal–organic framework when crystallized from water and methanol

When {2,2'-[(2-methyl-2-nitropropane-1,3-diyl)diimino]diacetato}copper(II), [Cu(C(8)H(13)N(3)O(6))], (I), was crystallized from a binary mixture of methanol and water, a monoclinic two-dimensional water- and methanol-solvated metal-organic framework (MOF) structure, distinctly different from the known orthorhombic one-dimensional coordination polymer of (I), was isolated, namely catena-poly[[copper(II)-mu(3)-2,2'-[(2-methyl-2-nitropropane-1,3-diyl)diimino]diacetato] methanol 0.45-solvate 0.55-hydrate], {[Cu(C(8)H(13)N(3)O(6))].0.45CH(3)OH.0.55H(2)O}(n), (II). The monoclinic structure of (II) comprises centrosymmetric dimers stabilized by a dative covalent Cu(2)O(2) core and intramolecular N-H...O hydrogen bonds. Each dimer is linked to four neighbouring dimers via symmetry-related (opposing) pairs of bridging carboxylate O atoms to generate a ;diamondoid' net or two-dimensional coordination network. Tight voids of 166 A(3) are located between these two-dimensional MOF sheets and contain a mixture of water and methanol with fractional occupancies of 0.55 and 0.45, respectively. The two-dimensional MOF sheets have nanometre-scale spacings (11.2 A) in the crystal structure. Hydrogen-bonding between the methanol/water hydroxy groups and a Cu-bound bridging carboxylate O atom apparently negates thermal desolvation of the structure below 358 K in an uncrushed crystal of (II).

Crystal-to-crystal transformation from a chain polymer to a two-dimensional network by thermal desolvation

Single-crystal to single-crystal transformation of a new lead(II) coordination polymer with ligands 8-hydroxyquinoline (8-Quin) and nitrate, [Pb2(8-Quin)2(NO3)2(MeOH)] () to [Pb(8-Quin)(NO3)] (1beta), is reported and the structures of and determined by X-ray crystallography.