Cycloaddition of Phenyltriazolinedione with Carbazole-Alkynes and Yne-Carbamates to Access Diazacyclobutenes.

Previously, we described the synthesis of stable, bicyclic examples of the rather rare diazacyclobutene (DCB) motif by means of a cycloaddition between triazolinediones and electron-rich thiolated alkynes. Here, we report the investigation of the cycloaddition of triazolinediones with related electron-rich yne-carbamates and carbazole-alkynes. Bicyclic DCBs arising from yne-carbamates were isolated in 8-65% yield, while those arising from carbazole-alkynes were isolated in 28-59% yield. Mechanistic studies and characterization of isolable byproducts shed light on the underlying issues leading to poor to moderate yields.

Synthesis, Structures, and Magnetic Investigations of Nickel Phosphates: Ni2(PO4)(OH), Ni7(PO4)3(HPO4)(OH)3, and NaNiPO4 Including Potential Haldane Behavior.

Three novel nickel-phosphate structures are reported, Ni2(PO4)(OH) (I), Ni7(PO4)3(HPO4)(OH)3 (II), and NaNiPO4 (III). Each new system was prepared via a high-temperature hydrothermal synthesis at 600-650 °C. All three compounds are built of quasi-one-dimensional (quasi-1-D) Ni2+ containing chains with varying phosphate bridging modes and were characterized by single crystal X-ray diffraction and magnetic susceptibility. All three compounds display very different magnetic behavior. Anisotropic magnetic data is reported for Ni2(PO4)(OH) (I) exhibiting slow antiferromagnetic ordering in the high-temperature regime with substructures that begin to form below 32 K at different field strengths. These characteristics affirm I as being one of the few Haldane-like material candidates. The Ni7(PO4)3(HPO4)(OH)3 (II) material is a member of the unusual ellenbergerite structural family and displays complex inter- and intrachain magnetic interactions while NaNiPO4 (III) shows antiferromagnetic ordering near 18 K. This magnetic behavior is correlated with their structures.

Twisted and Disconnected Chains: Flexible Linear Tetracuprous Arrays and a Decanuclear CuI Cluster as Blue- and Green/Yellow-Light Emitters.

Defined arrays of transition metal ions embedded in tailored polydentate ligand scaffolds allow for a systematic design of their physical properties. Such molecular strings of closed-shell transition metal centers are particularly interesting for Group 11 metal ions in the oxidation state +1 if they undergo metallophilic d10···d10 contact interactions since these clusters are oftentimes efficient photoluminescence (PL) emitters. Copper is particularly attractive as a sustainable earth-abundant coinage metal source and because of the ability of several CuI complexes to serve as powerful thermally activated delayed fluorescence (TADF) emitters in molecular/organic light-emitting devices (OLEDs). Our combined synthetic, crystallographic, photophysical, and computational study describes a straight tetracuprous array possessing a centrally disconnected CuI2···CuI2 chain and a continuous helically bent CuI4 complex. This molecular helix undergoes a facile rearrangement in diethyl ether solution, yielding an unprecedented nanosized CuI10 cluster (2.9 × 2.0 nm) upon crystallization. All three clusters show either bright blue phosphorescence, TADF, or green/yellow multiband phosphorescence with quantum yields between 6.5 and 67%, which is persistent under hydrostatic pressure up to 30 kbar. Temperature-dependent PL investigations in combination with time-dependent density-functional theory (TD-DFT) calculations and void space analyses of the crystal packings complement a comprehensive correlation between the molecular structures and photoluminescence properties.

Design Strategies for Luminescent Titanocenes: Improving the Photoluminescence and Photostability of Arylethynyltitanocenes.

Complexes that undergo ligand-to-metal charge transfer (LMCT) to d0 metals are of interest as possible photocatalysts. Cp2Ti(C2Ph)2 (where C2Ph = phenylethynyl) was reported to be weakly emissive in room-temperature (RT) fluid solution from its phenylethynyl-to-Ti 3LMCT state but readily photodecomposes. Coordination of CuX between the alkyne ligands to give Cp2Ti(C2Ph)2CuX (X = Cl, Br) has been shown to significantly increase the photostability, but such complexes are not emissive in RT solution. Herein, we investigate whether inhibition of alkyne-Ti-alkyne bond compression might be responsible for the increased photostability of the CuX complexes by investigating the decomposition of a structurally constrained analogue, Cp2Ti(OBET) (OBET = o-bis(ethynyl)tolane). To investigate the mechanism of nonradiative decay from the 3LMCT states in Cp2Ti(C2Ph)2CuX, the photophysical properties were investigated both upon deuteration and upon rigidifying in a poly(methyl methacrylate) film. These investigations suggested that inhibition of structural rearrangement may play a dominant role in increasing emission lifetimes and quantum yields. The bulkier Cp*2Ti(C2Ph)2CuBr was prepared and is emissive at 693 nm in RT THF solution with a photoluminescent quantum yield of 1.3 × 10-3 (τ = 0.18 µs). Time-dependent density functional theory (TDDFT) calculations suggest that emission occurs from a 3LMCT state dominated by Cp*-to-Ti charge transfer.

New Fluorine-Containing Diamine Monomers for Potentially Improved Polyimides.

Two new fluorine-containing diamine monomers were designed with the goal of reducing charge transfer complex (CTC) interactions between neighboring chains in polyimides (i.e., high transparency/low color) while hopefully maintaining the well-known thermal stability and flexibility generally associated with polyimides. The proposed diamines have been prepared through (1) the functionalization of 1,3-bis[(pentafluorobenzyl)oxy]benzene with 4-aminophenol and (2) the addition of 2-chloro-5-nitrobenzotrifluoride to 4,4'-bicyclohexanol followed by reduction of the resulting dinitro compound. The new compounds have been characterized by multinuclear NMR and IR spectroscopy and high-resolution liquid chromatography-mass spectrometry as well as single-crystal X-ray diffraction on the new diamine prepared from 4,4'-bicyclohexanol. Not only was the structure of the proposed new diamine confirmed, but another interesting example of hydrogen bonding between an N-H proton and the π-system of an aromatic ring was observed and documented. Initial polymerizations have been carried out via the two-step imidization process.

Role of the Trifluoropropynyl Ligand in Blue-Shifting Charge-Transfer States in Emissive Pt Diimine Complexes and an Investigation into the PMMA-Imposed Rigidoluminescence and Rigidochromism.

Square-planar PtII complexes are of interest as dopants for the emissive layer of organic light-emitting diodes. Herein, the photophysics of three Pt bipyridyl complexes with the strongly e- withdrawing, high-field, 3,3,3-trifluoropropynyl ligand has been investigated. One complex, (phbpy)PtC2CF3 (phbpy = 6-phenyl-2,2'-dipyridyl), has also been characterized by single-crystal X-ray diffraction. All complexes reported are emissive in both RT CH2Cl2 solution (ΦPL = 0.007 to 0.027) and PMMA film (ΦPL = 0.25 to 0.42). The trifluoropropynyl ligand elevates the energy of the MLCT and LL'CT states above that of the IL π-π* state, resulting in IL emission in all cases. The emission energies of the trifluoropropynyl compounds are also blue-shifted relative to the analogous pentafluorophenylethynyl compounds, suggesting that the trifluoropropynyl ligand is one of the most electron-withdrawing alkynyl ligands. Rate constants for radiative and nonradiative deactivation were determined from experimentally determined values of ΦPL and excited-state lifetimes in both solution and PMMA films. The increase in ΦPL upon incorporation into PMMA film (rigidoluminescence) results from a decrease in the rate constant for non-radiative relaxation. Experimental activation energies for excited-state decay in combination with TDDFT are consistent with the rigidoluminescence resulting from an increase in the energy of the non-emissive triplet metal-centered state. Two of the complexes investigated, (Ph2bpy)Pt(C2CF3)2 and (t-Bu2bpy)Pt(C2CF3)2, where t-Bu2bpy = 4,4'-di-tert-butyl-2,2'-dipyridyl and Ph2bpy = 4,4'-diphenyl-2,2'-dipyridyl, exhibit concentration-dependent excimer emission (orange) along with monomer emission (blue), enabling fine-tuning of the emission color. However, excimer emission was absent in cured PMMA films up to the solubility limit for solution processing of (Ph2bpy)Pt(C2CF3)2 in CH2Cl2, demonstrating the diffusional nature of excimer formation.

Photochemistry and Photophysics of Charge-Transfer Excited States in Emissive d10/d0 Heterobimetallic Titanocene Tweezer Complexes.

Transition-metal complexes that undergo ligand-to-metal charge transfer (LMCT) to d0 metals are of interest as possible photocatalysts due to the lack of deactivating d-d states. Herein, the synthesis and characterization of nine titanocene complexes of the formula Cp2Ti(C2Ar)2·MX (where Ar = phenyl, dimethylaniline, or triphenylamine; and MX = CuCl, CuBr, or AgCl) are presented. Solid-state structural characterization demonstrates that MX coordinates to the alkyne tweezers and CuX coordination has a greater structural impact than AgCl. All complexes, including the parent complexes without coordinated MX, are brightly emissive at 77 K (emission max between 575 and 767 nm), with the coordination of MX redshifting the emission in all cases except for the coordination of AgCl into Cp2Ti(C2Ph)2. TDDFT investigations suggest that emission is dominated by arylalkynyl-to-titanium 3LMCT in all cases except Cp2Ti(C2Ph)2·CuBr, which is dominated by CuBr-to-Ti charge transfer. In room-temperature fluid solution, only Cp2Ti(C2Ph)2 and Cp2Ti(C2Ph)2·AgCl are emissive, albeit with photoluminescent quantum yields ≤2 × 10-4. The parent complexes photodecompose in room-temperature solution with quantum yields, Φrxn, between 0.25 and 0.99. The coordination of MX decreases Φrxn by two to three orders of magnitude. There is a clear trend that Φrxn increases as the emission energy increases. This trend is consistent with a competition between energy-gap-law controlled nonradiative decay and thermally activated intersystem crossing between the 3LMCT state and the singlet transition state for decomposition.

Ln2 (SeO3 )2 (SO4 )(H2 O)2 (Ln=Sm, Dy, Yb): A Mixed-Ligand Pathway to New Lanthanide(III) Multifunctional Materials Featuring Nonlinear Optical and Magnetic Anisotropy Properties.

Bottom-up assembly of optically nonlinear and magnetically anisotropic lanthanide materials involving precisely placed spin carriers and optimized metal-ligand coordination offers a potential route to developing electronic architectures for coherent radiation generation and spin-based technologies, but the chemical design historically has been extremely hard to achieve. To address this, we developed a worthwhile avenue for creating new noncentrosymmetric chiral Ln3+ materials Ln2 (SeO3 )2 (SO4 )(H2 O)2 (Ln=Sm, Dy, Yb) by mixed-ligand design. The materials exhibit phase-matching nonlinear optical responses, elucidating the feasibility of the heteroanionic strategy. Ln2 (SeO3 )2 (SO4 )(H2 O)2 displays paramagnetic property with strong magnetic anisotropy facilitated by large spin-orbit coupling. This study demonstrates a new chemical pathway for creating previously unknown polar chiral magnets with multiple functionalities.

Crystal Engineering Using Polyiodide Halogen and Chalcogen Bonding to Isolate the Phenothiazinium Radical Cation and Its Rare Dimer, 10-(3-Phenothiazinylidene)phenothiazinium.

Utilizing facile one-electron oxidation of 10H-phenothiazine by molecular diiodine, the solid-state structure of the 10H-phenothiazinium radical cation was obtained in three cation:iodide ratios, as well as its THF and acetone solvates. Oxidation of 10H-phenothiazine with molecular diiodine in DMSO or DMF provided the structure of the radical coupling product 10-(3-phenothiazinyldene)phenothiazinium, which has not been crystallographically characterized to date. The radical cations were balanced by a mixture (I7 )- , (I5 )- , (I3 )- , and I- anions, where a variety of chalcogen, halogen, and hydrogen bonding interactions stabilize the structures to reveal these interesting cationic species.

Exploring the Role of Intramolecular Interactions in the Suppression of Quantum Tunneling of the Magnetization in a 3d-4f Single-Molecule Magnet.

Hydroxide-bridged FeIII4LnIII2 clusters having the general formula [Fe4Ln2(µ3-OH)2(mdea)6(SCN)2(NO3)2(H2O)2]·4H2O·2MeCN {Ln = Y (1), Dy (2), mdea = N-methyldiethanolamine} were synthesized and magnetically characterized. The thermal relaxation of the magnetization for 2 and the diluted FeIII4DyIIIYIII complex 3 (with and without applied field) has been analyzed. The diluted sample shows a dominant QTM at low temperatures that can be removed with a 0.15 T dc field. Both 2 and 3 show moderately high Ueff barriers and exhibit hysteresis loops until 5 K.

Ligand-to-Metal Charge-Transfer Photophysics and Photochemistry of Emissive d0 Titanocenes: A Spectroscopic and Computational Investigation.

Complexes with ligand-to-metal charge-transfer (LMCT) excited states involving d0 metals represent a new design for photocatalysts. Herein, the photochemistry and photophysics of d0 titanocenes of the type Cp2Ti(C2R)2, where C2R = ethynylphenyl (C2Ph), 4-ethynyldimethylaniline (C2DMA), or 4-ethynyltriphenylamine (C2TPA), have been investigated. Cp2Ti(C2Ph)2 and Cp2Ti(C2DMA)2 have also been characterized by single-crystal X-ray diffraction. The two aryl rings in Cp2Ti(C2DMA)2 are nearly face-to-face in the solid state, whereas they are mutually perpendicular for Cp2Ti(C2Ph)2. All three complexes are brightly emissive at 77 K but photodecompose at room temperature when irradiated into their lowest-energy absorption band. The emission wavelengths and photodecomposition quantum yields are as follows: Cp2Ti(C2Ph)2, 575 nm and 0.65; Cp2Ti(C2TPA)2, 642 nm and 0.42; Cp2Ti(C2DMA)2, 672 nm and 0.25. Extensive benchmarking of the density functional theory (DFT) model against the structural data and of the time-dependent DFT (TDDFT) model against the absorption and emission data was performed using combinations of 13 different functionals and 4 basis sets. The model that predicted the absorption and emission data with the greatest fidelity utilized MN15/LANL2DZ for both the DFT optimization and the TDDFT. Computational analysis shows that absorption involves a transition to a 1LMCT state. Whereas the spectroscopic data for Cp2Ti(C2TPA)2 and Cp2Ti(C2DMA)2 are well modeled using the optimized structure of these complexes, Cp2Ti(C2Ph)2 required averaging of the spectra from multiple rotamers involving rotation of the Ph rings. Consistent with this finding, an energy scan of all rotamers showed a very flat energetic surface, with less than 1.3 kcal/mol separating the minimum and maximum. The computational data suggest that emission occurs from a 3LMCT state. Optimization of the 3LMCT state demonstrates compression of the C-Ti-C bond angle, consistent with the known products of photodecomposition.

Polymorphism, Halogen Bonding, and Chalcogen Bonding in the Diiodine Adducts of 1,3- and 1,4-Dithiane.

Through variations in reaction solvent and stoichiometry, a series of S-diiodine adducts of 1,3- and 1,4-dithiane were isolated by direct reaction of the dithianes with molecular diiodine in solution. In the case of 1,3-dithiane, variations in reaction solvent yielded both the equatorial and the axial isomers of S-diiodo-1,3-dithiane, and their solution thermodynamics were further studied via DFT. Additionally, S,S'-bis(diiodo)-1,3-dithiane was also isolated. The 1:1 cocrystal, (1,4-dithiane)·(I2) was further isolated, as well as a new polymorph of S,S'-bis(diiodo)-1,4-dithiane. Each structure showed significant S···I halogen and chalcogen bonding interactions. Further, the product of the diiodine-promoted oxidative addition of acetone to 1,4-dithiane, as well as two new cocrystals of 1,4-dithiane-1,4-dioxide involving hydronium, bromide, and tribromide ions, was isolated.

Halogen Bonding in Dithiane/Iodofluorobenzene Mixtures: A New Class of Hydrophobic Deep Eutectic Solvents.

While research into deep eutectic solvents (DESs) has expanded over the previous two decades, the focus has remained on the utilization of hydrogen bond donors in these systems. Additionally, the majority of the known DESs rely on at least one ionic component. Through the combination of 1,3-dithiane and 1,2-diiodo-3,4,5,6-tetrafluorobenzene (1,2-F4 DIB), we report the first known DES based on halogen bonding. This mixture remains a liquid, with a eutectic melting temperature of 13.7 °C over a range of 1,3-dithiane mole fraction (0.35 to 0.75). Additionally, cocrystals of 1,3- and 1,4-dithiane with 1,2-, 1,3-, and 1,4-F4 DIB, as well as 1,3,5-trifluoro-2,4,6-triiodobenzene were studied via single-crystal X-ray diffraction. These data reveal a wide range of halogen bonding strengths (0.85

Alkali Transition-Metal Molybdates: A Stepwise Approach to Geometrically Frustrated Systems.

Materials with triangular arrangements of transition metal ions are of great interest for their complex magnetism resulting from geometric frustration. This paper describes the stepwise formation of kagome lattices of open shell transition-metal ions from half-delta chains to delta/sawtooth chains, and finally kagome nets. The systems can be viewed as a testbed for magnetic studies since a variety of spin states can be introduced across the same structure type, and progress through increasing levels of structural complexity and dimensionality. The synthetic and structural development of this continuum is studied here in well-formed single crystals of A2 M3 (MoO4 )3 (OH)2 (A=K, Rb; M=Mn, Co), CsM2 (MoO4 )2 (OH) (M=Mn, Fe, Co, Zn), and KM3 (MoO4 )2 O(OH) (M=Mn).

Chemistry of Metal Silicates and Germanates: The Largest Metal Polygermanate, K11Mn21Ge32O86(OH)9(H2O), with a 76 Å Periodic Lattice.

An examination of manganese silicates and germanates revealed unusual structural motifs and extremely different chemistries, with identical hydrothermal reactions forming K2Mn2Si3O9 versus K11Mn21Ge32O86(OH)9(H2O). The germanate is exceptional in both its c-axis length (exceeding 76 Å) and unit cell volume (nearly 18000 Å3), the largest known polygermanate structure to our knowledge.

Highly Luminescent Heavier Main Group Analogues of Boron-Dipyrromethene.

The preparation and photophysical properties of two heavier main group element analogues of boron-dipyrromethene (BODIPY) chromophores are described. Specifically, we have prepared dipyrrin complexes of dichlorogallate (GADIPY) or phenylphosphenium (PHODIPY) units. Whereas cationic PHODIPY is labile, decomposing to a phosphine over time, GADIPY is readily prepared in good yield as a crystalline solid having moderate air- and water-stability. Crystallographically characterized GADIPY displays intense green photoluminescence (λem = 505 nm, Φem = 0.91 in toluene). These inaugural heavier main group element analogues of BODIPY offer a glimpse into the potential for elaboration to a panoply of chromophores with diverse photophysical properties.

Cycloaddition/Electrocyclic Ring Opening Sequence between Alkynyl Sulfides and Azodicarboxylates To Provide N,N-Dicarbamoyl 2-Iminothioimidates.

The α-oxidized thioimidates are useful bidentate ligands and are important motifs in pharmaceuticals, pesticides, and fungicides. Despite their broad utility, a direct route for their synthesis has been elusive. Herein, we describe a one-step synthesis of N,N-dicarbamoyl 2-iminothioimidates from easily accessible thioacetylenes and commercially available azodicarboxylates (20 examples, ≤99% yield). Additionally, the mechanism of the transformation was extensively explored by variable-temperature NMR, in situ IR, and quantum mechanical simulations. These experiments suggest that the reaction commences with a highly asynchronous [2 + 2] cycloaddition, which leads to a four-membered diazacyclobutene intermediate with a barrier consistent with the observed reaction rate. This intermediate was then isolated for subsequent kinetic measurements, which yielded an experimental barrier within 1 kcal/mol of the calculated barrier for a subsequent 4π electrocyclic ring opening leading to the observed iminothioimidate products. This method represents the first direct route to α-oxidized thioimidates from readily accessible starting materials.

Magnetic Ground State Crossover in a Series of Glaserite Systems with Triangular Magnetic Lattices.

The magnetic properties are reported for three members of the glaserite series of compounds, Na2BaM(VO4)2, M = Mn, Mn0.6Co0.4, and Co. Large single crystals are grown using a high-temperature hydrothermal synthesis method. This structure type exhibits a triangular magnetic lattice in which M2+O6 octahedra are interconnected with nonmagnetic (VO4)3- groups. All the structures crystallize at room temperature with rigid trigonal symmetry (space group P3̅ m1); however, at lower temperatures both Na2BaMn(VO4)2 and Na2BaMn0.6Co0.4(VO4)2 undergo a structural transition to lower symmetry (monoclinic, C2/ c). The bulk magnetic measurements indicate that Mn- and Co-structures are antiferromagnetic and ferromagnetic, respectively. Na2BaMn0.6Co0.4(VO4)2 does not show any long-range ordering down to 0.5 K, although a broad heat capacity anomaly near 1.2 K suggests short-range magnetic order or freezing into a spin-glass-like state related to the chemical disorder and resulting competing magnetic interactions. The magnetic structures of Na2BaMn(VO4)2 and Na2BaCo(VO4)2 were determined using neutron powder diffraction. At zero magnetic field, Na2BaMn(VO4)2 possesses an antiferromagnetic structure with the moments ordered in a Néel-type arrangement and aligned along the C4 axis of the octahedra. Under applied magnetic field at 0.3 K, the evolution of the magnetic structure toward a fully polarized state is observed. Na2BaCo(VO4)2 represents a ferromagnetic (FM) magnetic structure with Co moments aligned parallel to the c-axis direction. The relationships between these structures and magnetic properties are discussed.

Single Crystals of Cubic Rare-Earth Pyrochlore Germanates: RE2Ge2O7 (RE = Yb and Lu) Grown by a High-Temperature Hydrothermal Technique.

Large single crystals of Yb2Ge2O7 in the cubic Fd3̅ m space group, are synthesized and characterized from a high-temperature hydrothermal method (650°C/200 MPa in 1 M KF). The cubic phase displays spin frustration and possibly nonclassical quantum-spin behavior at low temperature. This is the first report of single crystals of this important phase of size and quality suitable for single-crystal neutron diffraction.

A Cesium Rare-Earth Silicate Cs3 RESi6 O15 (RE=Dy-Lu, Y, In): The Parent of an Unusual Structural Class Featuring a Remarkable 57†ŠUnit Cell Axis.

The structure of Cs3 RESi6 O15 , where RE=Dy-Lu, Y, In, is unusual in that it contains octahedrally coordinated rare-earth ions; their relative orientation dictates the structure, as they rotate about the c-axis supported by the cyclic Si6 O15 framework. The repeat unit of the rotation is eight units generating a very long (ca. 57 Å) unit cell axis. This unusual repeat unit is created by the structural flexibility of the hexasilicate ring, which is in turn affected by the size of the rare earth ion as well as the size of alkali ion residing within the silicate layers. Previous work showed for the smaller Sc3+ ion, the rotation of the octahedra is not sufficient to achieve closure at an integral repeat unit and an incommensurate structure results. The products are prepared as large, high quality single crystals using a high-temperature (650 °C) hydrothermal method with CsOH and F- mineralizers. The presence of fluoride is essential to the formation of the product.