Search

Polyoxometalates (POMs) are recognized for their diverse structures and catalytic properties, yet their organometallic salts have not been thoroughly investigated. In this study, we synthesized salts of a Keggin-type POM with cationic sandwich complexes featuring various substituents, [ X ] 2 [SMo 12 O 40 ] [ X = Ru(C 5 H 5 )(C 6 H 5 R); R = H ( 1a ), Me ( 1b ), Bu ( 1c )], [Co(C 5 H 5 ) 2 ( 2 ), and Co(C 5 Me 5 ) 2 ( 3 )]. These salts exhibited similar structural characteristics, with each anion surrounded by 10 cations, forming two-dimensional sheet arrangements through O···O anion-anion contacts, except for the salt of 1c , which exhibited one-dimensional contact owing to the larger cation substituent. Additionally, [ 2 ](THA)[Mo 6 O 19 ], [ 3 ] 2 [Mo 6 O 19 ], and [ 3 ](THA)[SMo 12 O 40 ], containing the Lindqvist-type POM [Mo 6 O 19 ] and/or tetrahexylammonium (THA) cation, were obtained, with the packing structure of [ 3 ] 2 [Mo 6 O 19 ] closely resembling that of [ X ] 2 [SMo 12 O 40 ]. Solvate crystals of [ 1a ] 3 [PMo 12 O 40 ] were also prepared. [ 1a ] 2 [SMo 12 O 40 ] exhibits an electrical conductivity σ of 1.4 × 10 -7 S cm -1 at 373 K, which is 2 orders of magnitude higher than those of (THA) 2 [SMo 12 O 40 ] and [ 1a ]PF 6 .

Polyoxometalates (POMs), anionic nanosized oxoclusters that can be considered as fragments of metal oxides, have been extensively studied for their diverse composition and structure, showing promise in various fields such as catalysis and electronics. Proton conduction, relevant to catalysis and electronics, has attracted interest in materials chemistry, and POM anions are advantageous in terms of their proton carrier density and mobility. Recently, polar POMs have attracted attention for their unique ferroelectric behaviors, yet they have been little studied with regard to proton conduction, as their polarity has generally been believed to have a negative impact. Here, we propose that polar POMs can be used to align polar proton carriers, such as H 2 O and polymers, to construct efficient proton-conducting pathways. In this study, we present ionic crystals composed of polar Preyssler-type POMs ([X n + (H 2 O)P 5 W 30 O 110 ] (15- n )- , X n + = Ca 2+ , Eu 3+ ) and K + exhibiting ultrahigh proton conductivity surpassing 10 -2 S cm -1 , which is required for practical applications. In contrast, ionic crystals with nonpolar Preyssler-type POMs show an order of magnitude lower proton conductivity. Structural and spectroscopic studies combined with theoretical calculations reveal that proton carriers align with the aid of staggered arrays of polar POMs, forming a hydrogen-bonding network favorable for proton conduction. This study integrates molecular chemistry by the design of POMs and solid-state chemistry by exploring long-range proton conduction mechanisms, offering novel insights for future materials design.

To control three-dimensional (3D) cell spheroid formation, it is well-known the surface physicochemical and mechanical properties of cell culture materials are important; however, the formation and function of 3D cells are still unclear. This study demonstrated the precise control of the formation of 3D cells and 3D cell functions using diblock copolymers containing different ratios of a zwitterionic trimethylamine N -oxide group. The diblock copolymers were composed of poly( n -butyl methacrylate) (PBMA) as the hydrophobic unit for surface coating on a cell culture dish and stabilization in water, and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) as the precursor of N -oxide. The zwitterionic N -oxide converted from 0 to 100% using PDMAEMA. The wettability and surface zeta potential varied with different ratios of N -oxide diblock copolymer-coated surfaces, and the amount of protein adsorbed in the cell culture medium decreased monotonically with increasing N -oxide ratio. 3D cell spheroid formations were observed by seeding human umbilical cord mesenchymal stem cells (hUC-MSCs) in diblock copolymer-coated flat-bottom well plates, and the N -oxide ratio was over 40%. The cells proliferated in two-dimensions (2D) and did not form spheroids when the N -oxide ratio was less than 20%. Interestingly, the expression of undifferentiated markers of hUC-MSCs was higher on surfaces that adsorbed proteins to some extent and formed 50-150 μm spheroids in the range of 40-70% of N -oxide ratio. We revealed that a moderately protein-adsorbed surface allows precise control of spheroid formation and undifferentiated 3D cells and has potential applications for high-quality spheroids in regenerative medicine and drug screening.

Metal-organic framework (MOF) glasses have emerged as a new class of organic-inorganic hybrid glass materials. Considerable efforts have been devoted to unraveling the macroscopic dynamics of MOF glasses by studying their rheological behavior; however, their microscopic dynamics remain unclear. In this work, we studied the effect of vitrification on linker dynamics in ZIF-62 by solid-state 2 H nuclear magnetic resonance (NMR) spectroscopy. 2 H NMR relaxation analysis provided a detailed picture of the mobility of the ZIF-62 linkers, including local restricted librations and a large-amplitude twist; these details were verified by molecular dynamics. A comparison of ZIF-62 crystals and glasses revealed that vitrification does not drastically affect the fast individual flipping motions with large-amplitude twists, whereas it facilitates slow cooperative large-amplitude twist motions with a decrease in the activation barrier. These observations support the findings of previous studies, indicating that glassy ZIF-62 retains permanent porosity and that short-range disorder exists in the alignment of ligands because of distortion of the coordination angle.

Considerable efforts have been devoted to developing oxygen evolution reaction (OER) catalysts based on transition metal oxides. Polyoxometalates (POMs) can be regarded as model compounds of transition metal oxides, and cobalt-containing POMs (Co-POMs) have received significant interest as candidates. Nanocomposites based on Co-POMs have been reported to show high OER activities due to synergistic effects among the components; however, the role of each component is unclear due to its complex structure. Herein, we utilize porous ionic crystals (PICs) based on Co-POMs, which enable a composition-structure-function relationship to be established to understand the origin of the synergistic catalysis. Specifically, a Keggin-type POM [α-CoW 12 O 40 ] 6- and a Cr complex [Cr 3 O(OOCCH 2 CN) 6 (H 2 O) 3 ] + are implemented as PIC building blocks for the OER under nonbasic conditions. The potentially OER-active but highly soluble [α-CoW 12 O 40 ] 6- was successfully anchored in the crystalline PIC matrix via Coulomb interactions and hydrogen bonding induced by polar cyano groups of the Cr complex. The PIC exhibits efficient and sustained OER catalytic activity, while each building block is inactive. The Tafel slope of the linear sweep voltammetry curve and the relatively large kinetic isotope effect value suggest that elementary steps closely related to the OER rate involve single-electron and proton transfer reactions. Electrochemical and spectroscopic studies clearly show that the synergistic catalysis originates from the charge transfer from the Cr complex to [α-CoW 12 O 40 ] 6- ; the increased electron density of [α-CoW 12 O 40 ] 6- may increase its basicity and accelerate proton abstraction as well as enhance electron transfer to stabilize the reaction intermediates adsorbed on [α-CoW 12 O 40 ] 6- .

The exploration of composition-structure-function relationship in proton-conducting solids remains a challenge in materials chemistry. Polyoxometalate-based compounds have been long considered as candidates for proton conductors; however, their low structural stability and a large decrease in conductivity under reduced relative humidity (RH) have limited their applications. To overcome such limitations, the hybridization of polyoxometalates with proton-conducting polymers has emerged as a promising method. Besides, 4f lanthanide ions possess a high coordination number, which can be utilized to attract water molecules and to build robust frameworks. Herein, a Preyssler-type polyoxometalate functionalized with a 9-coordinate Eu 3+ (Eu[P 5 W 30 O 110 K] 11- ) is newly synthesized and combined with poly(allylamine) with amine moieties as protonation sites. The resulting robust crystalline composite exhibits an ultrahigh proton conductivity >10 -2 S cm -1 at 368 K and 90% RH, which is still >10 -3 S cm -1 at 50% RH, due to the strengthened and extended hydrogen-bonding network.

We first report the systematic control of the reactivity of H 2 O vapor in metal-organic frameworks (MOFs) with Pt nanocrystals (NCs) through ligand functionalization. We successfully synthesized Pt NCs covered with a water-stable MOF, UiO-66 (Pt@UiO-66), having different metal ions or functionalized ligands. The ligand functionalization of UiO-66 significantly affected the catalytic performance of the water-gas shift reaction, and the replacement of Zr 4+ ions with Hf 4+ ions in UiO-66 had no impact on the catalytic activity. The introduction of a -Br group lowered the reactivity of Pt@UiO-66 by nearly half, whereas the substitution of -Br with a -Me 2 group triply enhanced the activity. The origin of the enhanced catalytic activity was found to be the change in H 2 O activity in the UiO-66 pores by the ligand functionalization, which was investigated using H 2 O sorption, solid-state NMR, X-ray photoelectron spectroscopy, and in situ IR measurements. This work opens a new prospect to develop MOFs as a platform to activate H 2 O.

Two lanthanide-containing structurally analogous porous coordination polymers (PCPs) have been isolated with the general molecular formula [Ln 2 (L 1 ) 2 (H 2 O) 4 (ox)] n .4 nH 2 O (where L 1 = fumarate, ox = oxalate; Ln = Dy (1), Gd (2)). Thermogravimetric analysis (TGA) and TG-MS measurements performed on 1 and 2 suggest that not only the solvated water molecules in the crystal lattice but also the four coordinated water molecules on the respective lanthanides in 1 and 2 are removed upon activation. Due to the removal of the waters, 1 and 2 lost their crystallinity and became amorphous, as confirmed by powder X-ray diffraction (PXRD). We propose the molecular formula [Ln 2 (L 1 ) 2 (ox)] n for the amorphous phase of 1 and 2 (where Ln = Dy (1'), Gd (2')) on the basis of XANES, EXAFS, and other experimental investigations. Magnetization relaxation dynamics probed on 1 and 1' reveal two different relaxation processes with effective energy barriers of 53.5 and 7.0 cm -1 for 1 and 45.1 and 6.4 cm -1 for 1', which have been rationalized by detailed ab initio calculations. For the isotropic lanthanide complexes 2 and 2', magnetocaloric effect (MCE) efficiency was estimated through detailed magnetization measurements. We have estimated -Δ S m values of 52.48 and 41.62 J kg 1- K -1 for 2' and 2, respectively, which are one of the largest values reported for an extended structure. In addition, a 26% increase in -Δ S m value in 2' in comparison to 2 is achieved by simply removing the passively contributing (for MCE) solvated water molecule in the lattice and coordinated water molecules.

We describe the encapsulation of mobile proton carriers into defect sites in nonporous coordination polymers (CPs). The proton carriers were encapsulated with high mobility and provided high proton conductivity at 150 °C under anhydrous conditions. The high proton conductivity and nonporous nature of the CP allowed its application as an electrolyte in a fuel cell. The defects and mobile proton carriers were investigated using solid-state NMR, XAFS, XRD, and ICP-AES/EA. On the basis of these analyses, we concluded that the defect sites provide space for mobile uncoordinated H3PO4, H2PO4(-), and H2O. These mobile carriers play a key role in expanding the proton-hopping path and promoting the mobility of protons in the coordination framework, leading to high proton conductivity and fuel cell power generation.

Rational design to control the dynamics of molecular rotors in crystalline solids is of interest because it offers advanced materials with precisely tuned functionality. Herein, we describe the control of the rotational frequency of rotors in flexible porous coordination polymers (PCPs) using a solid-solution approach. Solid-solutions of the flexible PCPs [{Zn(5-nitroisophthalate)x(5-methoxyisophthalate)1-x(deuterated 4,4'-bipyridyl)}(DMF·MeOH)]n allow continuous modulation of cell volume by changing the solid-solution ratio x. Variation of the isostructures provides continuous changes in the local environment around the molecular rotors (pyridyl rings of the 4,4'-bipyridyl group), leading to the control of the rotational frequency without the need to vary the temperature.

Copolymerizations of 1,3-dehydroadamantane, 1, and various vinyl monomers were carried out in THF at room temperature. On mixing 1 with electron-deficient vinyl monomers, such as acrylonitrile and methyl acrylate, in the absence of any initiator, the copolymerization spontaneously proceeded to give alternating copolymers in 28-88% yield. By contrast, no reaction of 1 occurred at all when isobutyl vinyl ether or styrene was mixed under similar conditions. These contrastive results indicate the high electron density of a central sigma-bond in a strained [3.3.1]propellane derivative, 1. Alternating sequences of the resulting copolymers were characterized by NMR and MALDI-TOF-MS measurements. DSC and TGA measurements revealed the high thermal stability of the alternating copolymers containing bulky, stiff, and strain-free adamantane skeletons.