Temperature-dependent analysis of thermal motion, disorder and structures of tris(ethylenediamine)zinc(II) sulfate and tris(ethylenediamine)copper(II) sulfate

A series of dynamic single crystals of [MII(en)3]SO4 (M = Ni, Mn, and Cd) shows tunable dielectric properties and anisotropic thermal expansion

A series of dynamic single crystals with a chemical formula of [M^II(en)₃]SO₄ (en = ethylene and M^II = Ni^II, Mn^II, and Cd^II) was synthesized. As the temperature decreases, these materials exhibit dielectric switching in the vicinity of the phase transition point accompanied by anisotropic thermal expansion in the cell parameters as a consequence of the order-disorder structural change of SO2-4 in a cavity surrounded by five [M^II(en)₃]²⁺ complex cations. Because the variation of metal centers with different ionic radii changes the shape of the complex cation, which affects the distribution of hydrogen-bond interactions around the SO2-4, the dynamic motion of SO2-4 is substantially tuned. Correspondingly, the dielectric properties and anisotropic thermal expansion of materials were largely shifted, especially in the single crystals of [Mn^II(en)₃]SO₄, whose structural change is distinctly different from the crystals of Ni(II) and Cd(II). The detailed structural mechanism accounting for the different physical properties of these materials was discussed.

Probing Molecular Motions in Metal-Organic Frameworks by Three-Dimensional Electron Diffraction

Flexible metal-organic frameworks (MOFs) are known for their vast functional diversities and variable pore architectures. Dynamic motions or perturbations are among the highly desired flexibilities, which are key to guest diffusion processes. Therefore, probing such motions, especially at an atomic level, is crucial for revealing the unique properties and identifying the applications of MOFs. Nuclear magnetic resonance (NMR) and single-crystal X-ray diffraction (SCXRD) are the most important techniques to characterize molecular motions but require pure samples or large single crystals (>5 × 5 × 5 μm3), which are often inaccessible for MOF synthesis. Recent developments of three-dimensional electron diffraction (3D ED) have pushed the limits of single-crystal structural analysis. Accurate atomic information can be obtained by 3D ED from nanometer- and submicrometer-sized crystals and samples containing multiple phases. Here, we report the study of molecular motions by using the 3D ED method in MIL-140C and UiO-67, which are obtained as nanosized crystals coexisting in a mixture. In addition to an ab initio determination of their framework structures, we discovered that motions of the linker molecules could be revealed by observing the thermal ellipsoid models and analyzing the atomic anisotropic displacement parameters (ADPs) at room temperature (298 K) and cryogenic temperature (98 K). Interestingly, despite the same type of linker molecule occupying two symmetry-independent positions in MIL-140C, we observed significantly larger motions for the isolated linkers in comparison to those reinforced by π-π stacking. With an accuracy comparable to that of SCXRD, we show for the first time that 3D ED can be a powerful tool to investigate dynamics at an atomic level, which is particularly beneficial for nanocrystalline materials and/or phase mixtures.

A positive to negative uniaxial thermal expansion crossover in an organic benzothienobenzothiophene structure

Compound 6,6'-([1]benzothieno[3,2-b][1]benzothiophene-2,7-diyl)bis(butan-1-ol) (BTBT-C4OH) displays a continuous type 0 first-order isosymmetric phase transition at 200 K which is accompanied by a continuous change of the thermal expansion along the b axis from positive to negative. The equivalent isotropic atomic displacement parameters for all non-hydrogen atoms as well as all the eigenvalues of the anisotropic atomic displacement tensor show discontinuous behavior at the phase transition. The eigenvalues of the translational tensor in a rigid-body description of the molecule are all discontinuous at the phase transition, but the librational eigenvalues are discontinuous only in their temperature derivative. BTBT-C4OH displays a similar type of quasi-supercritical phase transition as bis(hydroxyhexyl)[1]benzothieno[3,2-b][1]benzothiophene (BTBT-C6OH), despite the difference in molecular packing and the very large difference in thermal expansion magnitudes.

Mechanoresponsive turn-on phosphorescence by a desymmetrization approach

The room-temperature phosphorescence (RTP) of metal-free organic crystals is normally quenched by mechanical stimulation. Herein, we demonstrate the opposite mechanoresponse of turn-on RTP. A desymmetrization of a C₂-symmetric 1,2-diketone creates space for molecular motion in the crystal, quenching the RTP from the crystal while maintaining that from the amorphous solid.

A unique copper coordination structure with both mono- and bi-dentate ethylenediamine ligands

A new crystal structure achieving penta-coordination using exclusively ethylenediamine ligands is discovered and characterized.

Making an order: the concerted alignment of [MOF5]2- (M = Nb and Ta) dipolar anions in one-dimensional coordination chains sustained by tris(3,4,5-trimethyl-1H-pyrazole)copper(II)

Electronic distortions, which are inherent in the oxide fluoride anions [MOF₅]^2- (M = Nb and Ta), provide an origin of polar molecular arrangements for the development of new polar second-harmonic-generating, piezo-, pyro- and ferroelectric materials. It is still a challenge to expand this approach to the realm of metal-organic polymers, while insufficient control over the environment of the [MOF₅]^2- units results in their orientational disorder and loss of polarity. The structures of catena-poly[[tris(3,4,5-trimethyl-1H-pyrazole-κN²)copper(II)]-μ-oxido-[tetrafluoridoniobium(V)]-μ-fluorido], [CuNbF₅O(C₆H₁₀N₂)₃]_n, (I), and its isostructural pentafluoridooxidotantalate(V) analogue, catena-poly[[tris(3,4,5-trimethyl-1H-pyrazole-κN²)copper(II)]-μ-oxido-[tetrafluoridotantalum(V)]-μ-fluorido], [CuTaF₅O(C₆H₁₀N₂)₃]_n, (II), are the first examples of the strict orientational order of [MOF₅]^2- (M = Nb and Ta) in one-dimensional coordination chains. A primary factor for the exact discrimination of one orientation of the anion over the other is strong and shape-selective multiple interactions of [MOF₅]^2- with the inherently acentric CuL₃²⁺ platform, with a set of two coordination and three N-H...F hydrogen bonds. In (I) and (II), the Cu²⁺ ions exhibit distorted square-pyramidal fivefold coordination formed by three pyrazole N atoms and the oxide O atom, defining the equatorial plane, and the anionic bridging F atom (which is trans with respect to the M-O bond) residing in the apical position. The inorganic bridges connect CuL₃²⁺ moieties into polar zigzag chains; the bulk polarity of the structure is eliminated by an antiparallel alignment of the individual chains. These chains are further connected through C-H...F hydrogen bonding and very weak C-H...π interactions of the organic ligands.

Triethanolaminate iron perchlorate revisited: change of space group, chemical composition and oxidation states in [Fe7(tea)3(tea-H)3](ClO4)2 (tea-H3 is triethanolamine)

The X-ray crystal structure of tris[N-(2-hydroxyethyl)-2,2'-iminodiethanolato]tris(2,2',2''-nitrilotriethanolato)tetrairon(II)triiron(III) bis(perchlorate), [Fe₇(C₆H₁₂NO₃)₃(C₆H₁₃NO₃)₃](ClO₄)₂ or [Fe₇(tea)₃(tea-H)₃](ClO₄)₂ (tea-H₃ is triethanolamine), is known from the literature [Liu et al. (2008). Z. Anorg. Allg. Chem. 634, 778-783] as a heptanuclear coordination cluster. The space group was given as I2₁3 and is reinvestigated in the present study. We find a new space-group symmetry of Pa-3 and could detect O-H hydrogens, which were missing in the original publication. Consequences on the Fe oxidation states are investigated with the bond-valence method, resulting in a mixed-valence core of four Fe^II and three Fe^III centres. Symmetry relationships between the two space groups and the average supergroup Ia-3 are discussed in detail.

Electrochemical Synthesis and Magnetic Properties of [Cu9W6]: The Ultimate Member of the Quindecanuclear Octacyanometallate-Based Transition-Metal Cluster?

[Cu9W6], synthesized by the electrochemical method, may be the ultimate member of the quindecanuclear octacyanometallate-based transition-metal cluster. Its single-crystal structure and magnetic properties were characterized.