Structure Transformation of Methylammonium Polyoxomolybdates via In-Solution Acidification and Solid-State Heating from Methylammonium Monomolybdate and Application as Negative Staining Reagents for Coronavirus Observation.

We prepared polyoxomolybdates with methylammonium countercations from methylammonium monomolybdate, (CH3NH3)2[MoO4], through two dehydrative condensation methods, acidifying in the aqueous solution and solid-state heating. Discrete (CH3NH3)10[Mo36O112(OH)2(H2O)14], polymeric ((CH3NH3)8[Mo36O112(H2O)14])n, and polymeric ((CH3NH3)4[γ-Mo8O26])n were selectively isolated via pH control of the aqueous (CH3NH3)2[MoO4] solution. The H2SO4-acidified solution of pH < 1 produced "sulfonated α-MoO3", polymeric ((CH3NH3)2[(MoO3)3(SO4)])n. The solid-state heating of (CH3NH3)2[MoO4] in air released methylamine and water to produce several methylammonium polyoxomolybdates in the sequence of discrete (CH3NH3)8[Mo7O24-MoO4], discrete (CH3NH3)6[Mo7O24], discrete (CH3NH3)8[Mo10O34], and polymeric ((CH3NH3)4[γ-Mo8O26])n, before their transformation into molybdenum oxides such as hexagonal-MoO3 and α-MoO3. Notably, some of their polyoxomolybdate structures were different from polyoxomolybdates produced from ammonium molybdates, such as (NH4)2[MoO4] or (NH4)6[Mo7O24], indicating that countercation affected the polyoxomolybdate structure. Moreover, among the tested polyoxomolybdates, (CH3NH3)6[Mo7O24] was the best negative staining reagent for the observation of the SARS-CoV-2 virus using transmission electron microscopy.

Jahn-Teller Switching of a Redox-Active Nickel(III) Center in a Homoleptic Thiolato Metalloligand Environment.

Treatment of nickel(II) nitrate with the iridium(III) metalloligand fac-[Ir(apt)3] (apt = 3-aminopropanethiolate) gave the trinuclear complex [Ni{Ir(apt)3}2](NO3)3 ([1Ir](NO3)3), in which the nickel center has a formal oxidation state of +III. Chemical or electrochemical oxidation and reduction of [1Ir](NO3)3 generated the corresponding trinuclear complexes [Ni{Ir(apt)3}2](NO3)4 ([1Ir](NO3)4) and [Ni{Ir(apt)3}2](NO3)2 ([1Ir](NO3)2) with one-electron oxidated and reduced states, respectively. Single-crystal X-ray crystallography revealed that the nickel center in [1Ir](NO3)3 is situated in a highly distorted octahedron due to Jahn-Teller effect, while the nickel center in each of [1Ir](NO3)4 and [1Ir](NO3)2 adopts a normal octahedral geometry. Crystals of [1Ir](NO3)3·2H2O are dehydrated on heating while retaining their single-crystallinity. The dehydration induces temperature-dependent dynamic disorder of the Jahn-Teller distortion at the nickel(III) center, which is largely quenched upon rehydration of the crystal.

Photoluminescent Layered Crystal Consisting of Anderson-Type Polyoxometalate and Surfactant toward a Potential Inorganic-Organic Hybrid Laser.

The hybridization of inorganic and organic components is a promising strategy to build functional materials. Among several functions, luminescence is an important function which should be considered for practical usage. Inorganic-organic hybrid luminescent materials have been investigated as phosphors, sensors, and lasers. Organic luminescent centers such as dye molecules have often been hybridized with inorganic matrices. Polyoxometalate anions (POMs) are effective inorganic luminescent centers due to their luminescent properties and structural designability. However, most luminescent POM components are limited to lanthanide-based POMs. In this report, a photoluminescent inorganic-organic hybrid crystal based on a non-lanthanide POM was successfully synthesized as a single crystal. Anderson-type hexamolybdochromate ([CrMo6O18(OH)6]3-, CrMo6) anion exhibiting emission derived from Cr3+ was utilized with n-dodecylammonium ([C12H25NH3]+, C12NH3) surfactant cation to obtain a photoluminescent hybrid crystal. The grown single crystal of C12NH3-CrMo6 comprised a distinct layered structure consisting of inorganic CrMo6 layers and interdigitated C12NH3 layers. In the CrMo6 layers, the CrMo6 anions were associated with water molecules by hydrogen bonding to form a densely packed two-dimensional network. Steady-state and time-resolved photoluminescence spectroscopy revealed that the C12NH3-CrMo6 hybrid crystal exhibited characteristic emission from the CrMo6 anion. Preliminary lasing properties were also observed for C12NH3-CrMo6, which shows the possibility of using the C12NH3-CrMo6 hybrid crystal as an inorganic-organic hybrid laser.

Hydrogen Bonding Propagated Phase Separation in Quasi-Epitaxial Single Crystals: A Pd-Br Molecular Insulator.

In condensed matter, phase separation is strongly related to ferroelasticity, ferroelectricity, ferromagnetism, electron correlation, and crystallography. These ferroics are important for nano-electronic devices such as non-volatile memory. However, the quantitative information regarding the lattice (atomic) structure at the border of phase separation is unclear in many cases. Thus, to design electronic devices at the molecular level, a quantitative electron-lattice relationship must be established. Herein, we elucidated a PdII-PdIV/PdIII-PdIII phase transition and phase separation mechanism for [Pd(cptn)2Br]Br2 (cptn = 1R,2R-diaminocyclopentane), propagated through a hydrogen-bonding network. Although the Pd···Pd distance was used to determine the electronic state, the differences in the Pd···Pd distance and the optical gap between Mott-Hubbard (MH) and charge-density-wave (CDW) states were only 0.012 Å and 0.17 eV, respectively. The N-H···Br···H-N hydrogen-bonding network functioned as a jack, adjusting the structural difference dynamically, and allowing visible ferroelastic phase transition/separation in a fluctuating N2 gas flow. Additionally, the effect of the phase separation on the spin susceptibility and electrical conductivity were clarified to represent the quasi-epitaxial crystals among CDW-MH states. These results indicate that the phase transitions and separations could be controlled via atomic and molecular level modifications, such as the addition of hydrogen bonding.

A Pseudorotaxane System Containing γ-Cyclodextrin Formed via Chiral Recognition with an AuI 6 AgI 3 CuII 3 Molecular Cap.

Solvent-mediated crystal-to-crystal transformations of [Au6 Ag3 Cu3 (H2 O)3 (d-pen)6 (tdme)2 ]3+ (d-[1(H2 O)3 ]3+ ; pen2- =penicillaminate, tdme=1,1,1-tris(diphenylphosphinomethyl)ethane) to form unique supramolecular species are reported. Soaking crystals of d-[1(H2 O)3 ]3+ in aqueous Na2 bdc (bdc2- =1,4-benzenedicarboxylate) yielded crystals containing d-[1(bdc)(H2 O)2 ]+ due to the replacement of a terminal aqua ligand in d-[1(H2 O)3 ]3+ by a monodentate bdc2- ligand. When γ-cyclodextrin (γ-CD) was added to aqueous Na2 bdc, d-[1(H2 O)3 ]3+ was transformed to d-[1(bdc@γ-CD)(H2 O)2 ]+ , where a γ-CD ring was threaded by a bdc2- molecule to construct a pseudorotaxane structure. While the use of dicarboxylates with an aliphatic carbon chain instead of bdc2- afforded analogous pseudorotaxanes, such pseudorotaxane species were not formed when crystals of [Au6 Ag3 Cu3 (H2 O)3 (l-pen)6 (tdme)2 ]3+ (l-[1(H2 O)3 ]3+ ) enantiomeric to d-[1(H2 O)3 ]3+ were soaked in aqueous Na2 bdc and γ-CD, affording only crystals containing l-[1(bdc)(H2 O)2 ]+ .

Racemic Tartrate/Malate Anions Combine with Racemic Complex Cations to Form Optically Active Ionic Crystals.

Spontaneous resolution has attracted continuing attention in various research fields since Pasteur's work on the crystallization behavior of racemic tartrate. Here, a unique example of this phenomenon is reported, involving ionic crystals generated from racemic RR/SS- tartrate or R/S-malate and racemic ΔΔ/ΛΛ-[Ag3 Rh2 (2-aminoethanethiolato)6 ]3+ (ΔΔ/ΛΛ-[1]3+ ) in water. RR- and SS-tartrate selectively recognize the ΛΛ and ΔΔ isomers of [1]3+ to produce ionic crystals of (ΛΛ-[1])2 (RR-tartrate)3 and (ΔΔ-[1])2 (SS-tartrate)3 , respectively, which can undergo spontaneous resolution. While spontaneous resolution also occurs when using R/S-malate, R- and S-malate select the opposite isomers of [1]3+ to give ionic crystals of (ΔΔ-[1])2 (R-malate)3 and (ΛΛ-[1])2 (S-malate)3 , respectively. In the presence of S-aspartate, (ΛΛ-[1])2 (R-tartrate)3 and (ΔΔ-[1])2 (S-tartrate)3 are preferentially crystallized from ΔΔ/ΛΛ-[1]3+ and RR/SS-tartrate at solution pH values of 6 and 10, respectively. This finding provides significant insight into the optical resolution of chemical species by spontaneous resolution and the origin of homochirality in nature.

Highly Porous Ionic Solids Consisting of AuI3CoIII2 Complex Anions and Aqua Metal Cations.

Treatment of Na3[Au3Co2(d-pen)6] (Na3[1]; d-H2pen = d-penicillamine) with M(OAc)2 (M = NiII, MnII) in water gave ionic crystals of [M(H2O)6]3[1]2 (2M) in which [1]3- anions are hydrogen-bonded with [M(H2O)6]2+ cations to form a 3D porous framework with a porosity of ca. 80%. Soaking crystals of 2Ni in its mother liquor afforded crystals of [Ni(H2O)6]2[{Ni(H2O)4}(1)2] (3Ni) in which [1]3- anions are connected to trans-[Ni(H2O)4]2+ and [Ni(H2O)6]2+ cations through coordination and hydrogen bonds, respectively, to form a 1D porous framework with a porosity ca. 60%. Further soaking crystals led to [{Ni(H2O)4}3(1)2] (4Ni), in which [1]3- anions are connected to cis-[Ni(H2O)4]2+ and trans-[Ni(H2O)4]2+ cations through coordination bonds in a dense framework with a porosity of ca. 30%. A similar two-step crystal-to-crystal transformation mediated by solvent proceeded when crystals of 2Mn were soaked in a mother liquor. However, the transformation of 2Mn generated [{Mn(H2O)4}(H1)] (4'Mn) as the final product, in which [H1]2- anions are connected to cis-[Mn(H2O)4]2+ cations through coordination bonds in a very dense framework with a porosity ca. 5% by way of [Mn(H2O)6]2[{Mn(H2O)4}(1)2] (3Mn), which is isostructural with 3Ni. While all the compounds adsorbed H2O and CO2 depending on the degree of their porosity, unusually large NH3 adsorption capacities were observed for 4Ni and 4'Mn, which have dense frameworks.

A 116-Nuclear Metallosupramolecular Cage-of-Cage Showing Multistep Single-Crystal-to-Single-Crystal Transformation.

Here a unique single-crystal-to-single-crystal (SCSC) transformation of a 116-nuclear AuI 72 CdII 40 NaI 4 cage-of-cage (2CdNa ) is reported, which was created from a trigold(I) metalloligand with d-penicillamine by way of a 9-nuclear AuI 6 CdII 3 cage (1). Cage-of-cage 2CdNa is composed of 12 cages of 1 that are linked by 4 Cd2+ and 4 Na+ ions, with its surface being covered by 12 NO3 - ions to form a discrete, spherical molecule with a diameter ca. 4.7 nm. In crystal 2CdNa , the cage-of-cage molecules are packed in a cubic lattice with a huge cell volume of ca. 4.5×105  Å3 , so as to have large interstices with diameters of more than 3 nm. Upon soaking crystals 2CdNa in aqueous Cu(NO3 )2 , all Cd2+ and Na+ were quickly exchanged by Cu2+ to produce an analogous AuI 72 CuII 44 cage-of-cage (2Cu ) in a SCSC manner. Prolonged soaking led to the SCSC transformation to another supramolecular structure (2'Cu ) consisting of 152-nuclear AuI 72 CuII 80 cage-of-cages that are alternately H-bonded with the AuI 72 CuII 44 cage-of-cages. 2'Cu showed the accommodation of MoO4 2- and the conversion of MoO4 2- to ß-Mo8 O26 4- in the crystal, with retention of single-crystallinity.

Dimensional Structures and Electrocatalytic Activities of Platinum(II)-Palladium(II)-Manganese(II) Coordination Polymers Controlled by Chloride versus Bromide.

Here we report the synthesis and structural characterization of heterotrimetallic (PtII2PdII2MnII2)n coordination polymers that show different dimensionalities and electrocatalytic activities depending on chloride and bromide employed in the system. The reaction of the PtII2PdII2 tetranuclear complex [Pd2Pt2(NH3)4(d-pen)4] (1), bearing free carboxylate groups, with Mn2+ in the presence of chloride produced the (PtII2PdII2MnII2)n coordination polymer [Mn2Cl2(H2O)6(1)]Cl2 (2Cl), in which the PtII2PdII2 units of 1 are linked by [MnCl(H2O)3]+ moieties in a 1:2 ratio to form a 2D sheetlike structure. The corresponding reaction in the presence of bromide also gave the (PtII2PdII2MnII2)n coordination polymer [Mn2(H2O)6(1)]Br4 (3Br), but 3Br adopted a 3D network structure via a 1:1 linkage of the PtII2PdII2 units with [Mn2(H2O)6]4+ moieties. These complexes showed appreciably different electrocatalytic activities for H2 evolution.

Charge-Separation-Type Ionic Crystals with Mixed AuI4CoIII2 and AuI4NiIICoIII Hexanuclear Complexes.

Treatment of a digold(I) metalloligand, [AuI2(dppe)(d-Hpen)2] (H2LAu; d-H2pen = d-penicillamine, dppe = 1,2-bis(diphenylphosphino)ethane), with a 1:1 mixture of Co(OAc)2 and Ni(OAc)2 under aerobic conditions resulted in the formation of three types of hexanuclear complexes: [CoIII2(LAu)2]2+, [NiIICoIII(LAu)2]+, and [NiII2(LAu)2]. The addition of NaNO3, M1NO3 (M1 = K, Rb, Cs), and M2(NO3)2 (M2 = Ca, Sr, Ba) to the reaction mixture led to co-crystallization of [CoIII2(LAu)2]2+ and [NiIICoIII(LAu)2]+ as a solid solution to form the charge-separation (CS)-type ionic crystals 1Na, 1M1, and 1M2, respectively, while [NiII2(LAu)2] independently crystallized as a single species (2). In 1Na, [CoIII2(LAu)2]2+ and [NiIICoIII(LAu)2]+ cations assemble in a 1:2 ratio to form a cationic supramolecular octahedron accommodating 4 H3O+ ions, while 10 nitrate ions are packed in each hydrophilic tetrahedral interstice of the crystal to form an anionic adamantane cluster. The overall structures of 1M1 and 1M2 are very similar to that of 1Na, having a CS-type structure composed of cationic supramolecular octahedra with a +12 charge and anionic inorganic clusters with a -10 charge. However, 1M1 contains M1 ions in place of the H3O+ ions in 1Na, and furthermore, a novel rhombic dodecahedron cluster composed of 14 nitrate ions, which encapsulates two M2 ions, is formed in each hydrophilic tetrahedral interstice in 1M2.

Platinum(II) Terpyridine Complex That Switches Its Photochemical Reactivity in Response to Its Chromic Behavior in the Crystalline State.

A platinum(II) terpyridine complex having an enantiopure lactate anion afforded hydrated crystals l- or d-1hyd containing infinite chains of interacting Pt centers, while their dehydration induced crystal-to-crystal transformation into l- or d-1dehyd, respectively, exhibiting less significant Pt-Pt and/or ligand-ligand interactions. That transformation was accompanied by changes in the color as well as the photochemical reactivity of the crystals, where l-1dehyd showed higher reactivity than l-1hyd in the presence of amines under visible-light irradiation.

Creation of Optically Pure Crystals from a Meso-Type Gold(I) Metalloligand with d- and l-Amino Acids: A Coordination Trick.

A unique example of a coordination system that creates optically pure crystals from a meso compound with d- and l-amino acids is reported. The 1:1 reaction of a newly prepared meso digold(I) complex, [Au2 (dcpe)(d-Hpen)(l-Hpen)] ([H2 1]), with Co(OAc)2 under aerobic conditions yielded a cationic AuI2 CoIII trinuclear complex, [Au2 Co(dcpe)(d-pen)(l-pen)]+ [2]+ , in which [1]2- acts as a hexadentate-N2 ,O2 ,S2 metalloligand to a CoIII center. Similar reactions with M(OAc)2 (M=Ni and Zn) produced analogous but neutral AuI2 MII complexes, [Au2 M(dcpe)(d-pen)(l-pen)] ([3M ]). Complexes [2]+ and [3M ] are chiral (C vs. A) at the octahedral CoIII and MII centers due to the arrangement of the N2 ,O2 ,S2 donor set. In addition, through spontaneous resolution, [3M ] gave optically pure C-[3M ] and A-[3M ] crystals, showing the creation of homochirality from meso-[1]2- and achiral M2+ through crystallization. Such a phenomenon was not observed for [2]+ , which gave a racemic compound containing both C-[2]+ and A-[2]+ .

Structural Investigation of Chemiresistive Sensing Mechanism in Redox-Active Porous Coordination Network.

By changing the rate of evaporation, two kinds of crystalline films composed of redox-active porous coordination networks (1 and 2) were selectively prepared on a gold-patterned substrate using a DMF solution of 2,5,8-tri(4-pyridyl)1,3-diazaphenalene and Cd(NO3)2. We found the highly sensitive humidity sensing ability of film 1. Single crystal structures and infrared spectroscopic analyses before and after hydration of a single crystal of 1 revealed the sensing mechanism: exchange of nitrate ions with water on Cd atoms occurred in hydrated conditions to generate a conductive cationic network.

Direct Observation of Ordered High-Spin-Low-Spin Intermediate States of an Iron(III) Three-Step Spin-Crossover Complex.

A neutral mononuclear Fe(III) complex [Fe(III) (H-5-Br-thsa-Me)(5-Br-thsa-Me)]⋅H2 O (1; H2 -5-Br-thsa-Me=5-bromosalicylaldehyde methylthiosemicarbazone) was prepared that exhibited a three-step spin-crossover (SCO) with symmetry breaking and a 14 K hysteresis loop owing to strong cooperativity. Two ordered intermediate states of 1 were observed, 4HS-2LS and 2HS-4LS, which exhibited reentrant phase-transition behavior. This study provides a new platform for examining multistability in SCO complexes.

Supramolecular interaction of fullerenes with a curved π-surface of a monomeric quadruply ring-fused porphyrin.

Molecular binding of fullerenes, C60 and C70, with the Zn(II) complex of a monomeric ring-fused porphyrin derivative (2-py) as a host molecule, which has a concave π-conjugated surface, has been confirmed spectroscopically. The structures of associated complexes composed of fullerenes and 2-py were explicitly established by X-ray diffraction analysis. The fullerenes in the 2:1 complexes, which consist of two 2-py molecules and one fullerene molecule, are fully covered by the concave surfaces of the two 2-py molecules in the crystal structure. In contrast, in the crystal structure of the 1:1 complex consisting of one 2-py molecule and one C60 molecule, the C60 molecule formed a π-π stacked pair with a C60 molecule in the neighboring complex using a partial surface, which was uncovered by the 2-py molecule. Additionally, the molecular size of fullerene adopted significantly affects the (1)H NMR spectral changes and the redox properties of 2-py upon the molecular binding.

Coassembly-Directed Fabrication of an Exfoliated Form of Alternating Multilayers Composed of a Self-assembled Organoplatinum(II) Complex-Fullerene Dyad.

The self-assembly of covalently linked dyad 1a of cyclometalated organoplatinum(II) complex and fullerene afforded alternating multilayers of electron-rich and -deficient molecular components. On the other hand, the coassembly of 1a with organoplatinum(II) complex 2 having no fullerene moiety gave an exfoliated form of the multilayers, by inhibiting the interdigitation of organoplatinum(II) complex moieties of 1a. The coassembled 1a/2 transports both of the photogenerated holes and electrons, while the self-assembled 1a allows only the transportation of electrons under the same conditions.

Reversible single-crystal-to-single-crystal photochemical formation and thermal cleavage of a cyclobutane ring.

A [2+2] cycloaddition reaction has been observed in a number of solids. The cyclobutane ring in a photodimerized material can be cleaved into olefins by UV light and heat. The high thermal stability of the metal-organic salt K2SDC (H2SDC = 4,4'-stilbenedicarboxylic acid) has been successfully utilized to investigate the reversible cleavage of a cyclobutane ring. The two polymorphs of K2SDC undergo reversible cyclobutane formation by UV light and cleavage by heat in cycles. Of these, one polymorph retains its single-crystal nature during the reversible processes. Polymorphs are known to show different physical properties and chemical reactivities. This work reveals that the retention of single-crystal nature is strongly associated with the packing of molecules, which is controlled by kinetics and thermodynamics. The photoemissive nature of the products makes this as a promising material for photoswitches and optical data storage devices.

Stereoselective synthesis of 6/7/6-fused heterocycles with multiple stereocenters via an internal redox reaction/inverse electron-demand hetero-Diels-Alder reaction sequence.

A highly stereoselective synthesis of fused heterocycles with multiple stereocenters via an internal redox reaction/inverse electron-demand hetero-Diels-Alder (IEDHDA) reaction sequence is described. The present reaction sequence has three interesting features: (1) complete control of two potentially competitive processes, i.e., hetero-Diels-Alder reaction and [1,5]-hydride shift; (2) one-shot construction of the complicated 6/7/6-fused heterocyclic structure having multiple stereocenters; and (3) high control of its stereoselectivity. When alkenylidene barbiturates with an allyl benzyl ether moiety were treated with a catalytic amount of Sc(OTf)3 and 2,2'-bipyridine, the internal redox reaction/IEDHDA reaction proceeded successively to afford 6/7/6-fused heterocycles in good chemical yields with good to excellent diastereoselectivities.

Divergent synthesis of multi-substituted phenanthrenes via an internal redox reaction/ring expansion sequence.

We report an effective synthetic route to multi-substituted phenanthrenes via an internal redox reaction/ring expansion sequence. The interesting feature of the present system is that it allows for the divergent synthesis of the target skeleton depending on the selected Lewis acid catalyst. When benzylidene malonates with a cyclic structure at the ortho-position were treated with BF3·OEt2, three sequential processes (internal redox reaction/elimination of the alkoxy group/ring expansion) proceeded to give phenanthrene derivatives in which the alkoxycarbonyl (CO2R) group and the alkyl (R) group were in close proximity to each other, in good chemical yields. In sharp contrast, treatment with Bi(OTf)3 exclusively led to the formation of another type of phenanthrene, whose R group was positioned distal to the CO2R group.

Ring-shaped Re(I) multinuclear complexes with unique photofunctional properties.

We synthesized for the first time a series of emissive ring-shaped Re(I) complexes (Re-rings) with various numbers of Re(I) units and various lengths of bridge ligands. The photophysical properties of the Re-rings could be varied widely through changes in the size of the central cavity. A smaller central cavity of the Re-rings induced intramolecular π-π interactions between the ligands and consequently caused a stronger emission and a longer lifetime of the excited state. The Re-rings can function as efficient and durable photosensitizers. The combination of a trinuclear Re-ring photosensitizer with fac-[Re(bpy)(CO)3(MeCN)](+) (bpy = 2,2'-bipyridine) as a catalyst photocatalyzed CO2 reduction with the highest quantum yield of 82%.