Variability in the Formation and Framework Polymorphism of Metal-organic Frameworks based on Yttrium(III) and the Bifunctional Organic Linker 2,5-Dihydroxyterephthalic Acid

Depending on the solvothermal reaction conditions, we obtained three different metal-organic frameworks with yttrium(III) as metal component and 2,5-dihdyroxyterepthalic acid (H₄dhtp) as bifunctional organic linker: Y₂(H₂dhtp)₃(dmf)₄ · (dmf)₂ (CPO-29) contains dinuclear, paddle-wheel like inorganic secondary building units (SBUs) connected by the organic linker to a network with α-Po topology, while Y₂(H₂dhtp)(dhtp)(dmf)₂ (CPO-30) and Y₂(H₂dhtp)(dhtp)(dmf)₂(H₂O)₂ · (H₂O)₄ (CPO-31) contain one-dimensional inorganic SBUs that differ in how the half- and fully deprotonated ligands are connected to and arranged around them. Only the carboxylic acid groups of the organic linker are deprotonated in CPO-29, while CPO-30 and CPO-31 contain both 2,5-dihydroxyterephthalate (H₂dhtp^2–) linkers and fully deprotonated 2,5-dioxidoterephthalate (dhtp^4–) linkers. All three compounds contain large volumes filled with solvent, but we were able to demonstrate permanence of porosity only for CPO-30. Variable temperature powder X-ray diffraction reveals that CPO-29 and CPO-31 undergo discontinuous phase transitions upon heating, and the flexibility of the framework structure indicated by these might be the reason for the inability to access the pore volume. Desolvated CPO-30 and CPO-31 are polymorphs, whose network structures differ in whether the H₂dhtp^2– and dhtp^4– linkers are located in cis or trans arrangement around the inorganic SBU.     

Pore-Scale Level Set Simulations of Capillary-Controlled Displacement with Adaptive Mesh Refinement

Transport in Porous Media - Multiphase flow simulations on imaged porous rock structures require numerical methods that are accurate and robust when applied on complex geometries. A key element in...     

On the application of a single‐crystal κ‐diffractometer and a CCD area detector for studies of thin films

A multipurpose six‐axis κ‐diffractometer, together with the brilliance of the ESRF light source and a CCD area detector, has been explored for studying epitaxial relations and crystallinity in thin film systems. The geometrical flexibility of the six‐axis goniometer allows measurement of a large volume in reciprocal space, providing an in‐depth understanding of sample crystal relationships. By a set of examples of LaAlO₃ thin films deposited by the atomic layer deposition technique, the possibilities of the set‐up are presented. A fast panoramic scan provides determination of the crystal orientation matrices, prior to more thorough inspection of single Bragg nodes. Such information, in addition to a broadening analysis of families of single reflections, is shown to correlate well with the crystallinity, crystallite size, strain and epitaxial relationships in the thin films. The proposed set‐up offers fast and easy sample mounting and alignment, along with crucial information on key features of the thin film structures.     

Structure and Polymorphism of M(thd)3 (M = Al,Cr, Mn,Fe, Co,Ga, and In)

Formation, crystal structure, polymorphism, and transition between polymorphs are reported for M(thd)₃, (M = Al, Cr, Mn, Fe, Co, Ga, and In) [(thd)^– = anion of H(thd) = C₁₁H₂₀O₂ = 2, 2, 6, 6‐tetramethylheptane‐3, 5‐dione]. Fresh crystal‐structure data are provided for monoclinic polymorphs of Al(thd)₃, Ga(thd)₃, and In(thd)₃. Apart from adjustment of the M–O_k bond length, the structural characteristics of M(thd)₃ complexes remain essentially unaffected by change of M. Analysis of the M–O_k, O_k–C_k, and C_k–C_k distances support the notion that the M–O_k–C_k–C_k–C_k–O_k– ring forms a heterocyclic unit with σ and π contributions to the bonds. Tentative assessments according to the bond‐valence or bond‐order scheme suggest that the strengths of the σ bonds are approximately equal for the M–O_k, O_k–C_k, and C_k–C_k bonds, whereas the π component of the M–O_k bonds is small compared with those for the O_k–C_k, and C_k–C_k bonds. The contours of a pattern for the occurrence of M(thd)₃ polymorphs suggest that polymorphs with structures of orthorhombic or higher symmetry are favored on crystallization from the vapor phase (viz. sublimation). Monoclinic polymorphs prefer crystallization from solution at temperatures closer to ambient. Each of the M(thd)₃ complexes subject to this study exhibits three or more polymorphs (further variants are likely to emerge consequent on systematic exploration of the crystallization conditions). High‐temperature powder X‐ray diffraction shows that the monoclinic polymorphs convert irreversibly to the corresponding rotational disordered orthorhombic variant above some 100–150 °C (depending on M). The orthorhombic variant is in turn transformed into polymorphs of tetragonal and cubic symmetry before entering the molten state. These findings are discussed in light of the current conceptions of rotational disorder in molecular crystals.     

Increased dimensionalities of zinc-diphenic acid coordination polymers by simultaneous or subsequent addition of neutral bridging ligands

Three coordination polymers containing zinc and diphenic acid (H2dpa) were synthesised by solvothermal reaction. Zn(dpa)(H2O) is a one-dimensional coordination polymer that consists of parallel ladder-like chains. One carboxylate group of the diphenic acid coordinates two zinc atoms forming a dinuclear unit which composes the steps of the ladder. The other carboxylate connects to a zinc atom in the next step of the ladder. The fourth coordination site at the zinc atom is occupied by water. Attempts to crosslink the chains by replacing the water molecule with the neutral ligands triethylenediamine (dabco) or 4,4'-bipyridyl lead to the compounds Zn2(dpa)2(dabco) and Zn(dpa)(4,4'-bpy). Their structures can be rationalised as being derived from action of the neutral ligand on Zn(dpa)(H2O), and while they are most conveniently prepared in a one-pot synthesis, it is also possible to obtain them by exposing Zn(dpa)(H2O) to the respective neutral ligand. Zn2(dpa)2(dabco) is a layered two-dimensional coordination polymer in which dinculear zinc carboxylate paddle wheel units and the dabco ligand form infinite linear chains. The chains are interconnected by the dpa unit. The structure of Zn(dpa)(4,4'-bpy) consists of two identical interpenetrating three-dimensional networks. In the network, helical Zn(dpa) chains are interconnected by the rigid 4,4'-bipyridine ligand. Thermogravimetric analysis indicates a high thermal stability of this coordination polymer with decomposition occurring in the range 350-450 degrees C. This is complemented by X-ray thermodiffractometry that indicates a phase transition at 337 degrees C and the final loss of crystallinity at 427 degrees C. The room temperature phase expands drastically along one axis and contracts along the other two axes on heating.     

Magnetic and structural properties of Cr1−tTitAs

The pseudobinary CrAsTiAs system has been investigated by X-ray and neutron diffraction and magnetic susceptibility measurements at temperatures between 10 and 1000 K. The phase diagram includes paramagnetic regions with the MnP-, NiAs-, and TiP-type structures and a low-temperature helimagnetic, MnP-type state for0.00 ≦ t ≦ 0.10 of Cr_1?tTi_tAs. The first-order para- to helimagnetic transition in Cr_1?tTi_tAs is accompanied by a hysteresis of 10–15 K. The results are discussed in relation to the findings for other Cr_1?tT_tAs(T =V, Mn, Fe, Co, Ni) andCrAs_1?xX_x (X = P, Sb, Se) phases.     

Deposition of thin films of organic-inorganic hybrid materials based on aromatic carboxylic acids by atomic layer deposition

Thin films of organic-inorganic hybrid materials have been grown by the atomic layer deposition (ALD) technique, using trimethylaluminium (TMA) and aromatic carboxylic acids such as 1,2-benzene dicarboxylic acid, 1,3-benzene dicarboxylic acid, 1,4-benzene dicarboxylic acid, 1,3,5-benzene tricarboxylic acid, 1,2,4,5-benzene tetracarboxylic acid as precursors. Growth rates as function of temperature show that all systems, with the exception of the benzoic acid-TMA system, possess ALD-windows and provides growth rates in the range of 0.25-1.34 nm/cycle. X-ray diffraction studies of the as-deposited films reveal their amorphous character, which is also supported by very low surface roughness as measured by atomic force microscopy. As-deposited films were investigated by Fourier Transform Infrared Spectroscopy proving that the deposited films are of a hybrid character.     

Syntheses,structures and magnetic properties of Mn(II) containing 3D polymeric networks

Two novel 3D coordination polymers {[Mn(aip)(DMF)]}_n, CPO-9, and {[Mn₃(Hatp)₂(atp)₂](H₂O)₂(DEF)₄}_n CPO-10 (aip = 5-aminoisophthalate, atp = 2-aminoterephthalate, DMF = dimethylformamide, DEF = diethylformamide) have been synthesized by solvothermal methods. Their properties have been studied by single-crystal X-ray diffraction, thermogravimetric analysis, high-temperature powder X-ray diffraction and magnetic susceptibility measurements. The crystal structure of CPO-9 is based on infinite chains of carboxylato-bridged five-coordinated Mn(II) ions that are crosslinked via the aip ligands to form a 3D structure. CPO-10 is based on linear trinuclear building units of carboxylato-bridged octahedral Mn(II) ions that are crosslinked by the atp ligands into a 3D structure. Both compounds have 1D channels that contain solvent molecules. The solvent accessible void volume for CPO-10 is 51.9% of the unit cell volume. For both compounds, however, the solvent molecules cannot be removed without the collapse of the structures into amorphous phases at 250 °C. The magnetic susceptibility measurements indicate antiferromagnetic couplings between the Mn(II) ions in both compounds. The magnetic data have been fitted using theoretical approaches.