Cationic Units Research Articles

Synthesis, X-ray structure, Hirshfeld, and antimicrobial studies of new Ag(I) complexes based on pyridine-type ligands

The two silver(I) complexes [Ag(3CNPy)2(CF3COO)]n (1) and [Ag(4BzPy)2]2(CF3COO)2 (2) where 3CNPy and 4BzPy are 3-cyanopyridine and 4-benzoylpyridine, respectively, were synthesized and characterized using elemental analysis, FTIR spectra and single crystal X-ray diffraction. Complex 1 is a 1D coordination polymer through the bridging and the highly symmetric CF3COO¯ group while 2 is a dinuclear complex through strong argentophilic interaction connecting the two [Ag(4BzPy)2] cationic units. In both complexes, the pyridine ligands are acting as monodentate N-donor. Hirshfeld surface analysis revealed the importance of the polar N···H (29.9%) and H···F (10.3%) hydrogen bonds in the molecular packing of 1. For 2, the nonpolar C···H (26.2%) and the polar O···H (15.6%) interactions dominate the crystal packing. Furthermore, both complexes showed π-π stacking interactions. Antimicrobial screening revealed that 3CNPy has no activity against all tested pathogens, while 1 has good antibacterial activity. Both Ag(I) complexes and 4BzPy showed remarkable antifungal activities against A. fumigatus and C. albicans compared to Ketoconazole as control.

Induction of Paraptosis by Cyclometalated Iridium Complex-Peptide Hybrids and CGP37157 via a Mitochondrial Ca2+ Overload Triggered by Membrane Fusion between Mitochondria and the Endoplasmic Reticulum.

We previously reported that a cyclometalated iridium (Ir) complex-peptide hybrid (IPH) 4 functionalized with a cationic KKKGG peptide unit on the 2-phenylpyridine ligand induces paraptosis, a relatively newly found programmed cell death, in cancer cells (Jurkat cells) via the direct transport of calcium (Ca2+) from the endoplasmic reticulum (ER) to mitochondria. Here, we describe that CGP37157, an inhibitor of a mitochondrial sodium (Na+)/Ca2+ exchanger, induces paraptosis in Jurkat cells via intracellular pathways similar to those induced by 4. The findings allow us to suggest that the induction of paraptosis by 4 and CGP37157 is associated with membrane fusion between mitochondria and the ER, subsequent Ca2+ influx from the ER to mitochondria, and a decrease in the mitochondrial membrane potential (ΔΨm). On the contrary, celastrol, a naturally occurring triterpenoid that had been reported as a paraptosis inducer in cancer cells, negligibly induces mitochondria-ER membrane fusion. Consequently, we conclude that the paraptosis induced by 4 and CGP37157 (termed paraptosis II herein) proceeds via a signaling pathway different from that of the previously known paraptosis induced by celastrol, a process that negligibly involves membrane fusion between mitochondria and the ER (termed paraptosis I herein).

Integrated Afterglow and Self-Trapped Exciton Emissions in Hybrid Metal Halides for Anti-Counterfeiting Applications.

0D hybrid metal halides (0D HMHs) are considered to be promising luminescent emitters. 0D HMHs commonly exhibit self-trapped exciton (STE) emissions originating from the inorganic metal halide anion units. Exploring and utilizing the emission features of the organic cation units in 0D HMHs is highly desired to enrich their optical properties as multifunctional luminescent materials. Here, tunable emissions from organic and inorganic units are successfully achieved in triphenylsulfonium (Ph3 S+ )-based 0D HMHs. Notably, integrated afterglow and STE emissions with adjustable intensities are obtained in (Ph3 S)2 Sn1- x Tex Cl6 (x= 0-1) via the delicate combination of [SnCl6 ]2- and [TeCl6 ]2- . Moreover, such a strategy can be readily extended to develop other HMH materials with intriguing optical properties. As a demonstration, 0D (Ph3 S)2 Zn1- x Mnx Cl4 (x= 0-1) are constructed to achieve integrated afterglow and Mn2+ d-d emissions with high efficiency. Consequently, these novel 0D HMHs with colorful afterglow and STE emissions are applied in multiple anti-counterfeiting applications.

Through-Space Electrostatic Effects of Positively Charged Substituents on the Hydrogen Evolution Reaction.

Elucidating the effects of various structural components on energy-related small molecule activation is of fundamental and practical significance. Herein the inhibition effect of positively charged substituents on the hydrogen evolution reaction (HER) was reported. With the use of Cu porphyrins 1-5 containing different numbers and locations of positively charged substituents, it was demonstrated that their electrocatalytic HER activities significantly decreased when more cationic units were located close to the Cu ion: the icat /ip (icat is the catalytic peak current, ip is the one-electron reduction peak current) value decreased from 38 with zero cationic unit to 15 with four closely located cationic units. Inspired by this result, Cu porphyrin 6, with four meso-phenyl groups each bearing a negatively charged para-sulfonic substituent, was designed. With these anionic units, 6 outperformed the other Cu porphyrins for electrocatalytic HER under the same conditions.

Synthesis, structure characterization and properties of a new oxidovanadium(IV) coordination polymer incorporating bridging (MoO4)2– and (Mo8O26)4– ligands

Abstract Hydrothermal synthesis, crystal structure and properties of a new heterometallic coordination polymer [(VO(terpy))4(MoO4)2(Mo8O26)]·2H2O (1) (terpy = 2,2′;6′,2″-terpyridine) are reported. Compound 1 contains two crystallographically unique vanadium(IV) atoms, bonded to a terminal oxido ligand and further coordinated to a terpy ligand. The three N atoms of terpy occupy the meridional sites of a distorted {VN3O3} octahedron. A γ-octamolybdate (Mo8O26)4– located on an inversion centre and a tetraoxidomolybdate (MoO4)2– function as bridging ligands. The μ3-bridging tridentate binding of (MoO4)2– leads to the formation of a {V4Mo2O12}4+ cationic unit consisting of an eight-membered heterometallic {Mo2V2O4} ring with protruding oxidovanadium handles. A pair of {V4Mo2O12}4+ units are bridged by the centrosymmetric (Mo8O26)4– ligand, resulting in the formation of an infinite chain of alternating {V4Mo2O12}4+ cations and (Mo8O26)4– anions.

Multivalent Supramolecular Assembly Based on a Triphenylamine Derivative for Near-Infrared Lysosome Targeted Imaging.

Near-infrared (NIR) targeted cell imaging has become a research hotspot due to the advantages of deeper tissue penetration, minimal interference from the background signals, and lower light damage. Herein, we report a multivalent supramolecular aggregate with NIR fluorescence emission, which was fabricated from triphenylamine derivatives (TPAs), cucurbit[8]uril (CB[8]), Si-rhodamine (SiR), and hyaluronic acid (HA). Interestingly, possessing a rigid luminescent core and cationic phenylpyridinium units linked by flexible alkyl chains, the tripaddle hexacationic TPA could bind with CB[8] at a 2:3 stoichiometric ratio to form a network-like multivalent assembly with enhanced red luminescence. Such organic two-dimensional network-like aggregate further co-assembled with the energy acceptor SiR and cancer cell targeting agent HA, leading to nanoparticles with NIR emission at 675 nm via an intermolecular energy transfer pathway. Furthermore, the obtained multivalent supramolecular aggregate was successfully applied in lysosome targeted imaging toward A549 cancer cells, which provides a convenient strategy for NIR targeted cell imaging.

Cyclic topology enhances the killing activity of polycations against planktonic and biofilm bacteria.

Bacterial biofilms, as a fortress to protect bacteria, enhance resistance to antibiotics because of their limited penetration, which has become a major threat to current anti-infective therapy. Antimicrobial polycations have received wide attention to kill planktonic bacteria because of their unique antimicrobial mechanism without drug resistance but it is still hard to kill the bacteria in the deep of the biofilm. Unlike linear polymers, the cyclic topology has been demonstrated with enhanced penetration in tissues, which is attributed to the lack of end groups, constrained conformation and a smaller hydrodynamic volume, opening a new sight of polycations in the antibacterial application against biofilms. Here, polycations with different topologies including linear and cyclic polycations were synthesized and their killing activity against planktonic and biofilm bacteria was studied. The experimental results showed the enhanced antibacterial activity of cyclic polycations for planktonic bacteria, which is presumably attributed to their smaller hydrodynamic volume, higher local density of positive charge and more interactions between cation units and the bacterial membrane than their linear analogues. Besides, cyclic polycations exhibit enhanced killing effect for biofilm bacteria and inhibition effect for biofilms with 5-7 times and 2-3 times enhancements than the linear polycations, respectively. Furthermore, an Escherichia coli infection model on mice was established and the therapeutic effects of cyclic and linear polycations were evaluated. Compared with the linear polycations, the cyclic polycations exhibited enhanced antibacterial activity with an ∼4 times increase, promoting the healing of the infected wounds. This work provides a new perspective in the development of antimicrobial polycations, which are promising therapeutic agents to kill planktonic and biofilm bacteria without drug resistance.

Immobilization of Methyl Orange and Methylene Blue within the Matrix of Charge-Imbalanced Amphoteric Nanogels and Study of Dye Release Kinetics as a Function of Temperature and Ionic Strength

Cross-linked polyampholyte nanogels consisting of neutral N-isopropylacrylamide (NIPAM), negatively charged sodium salt of 2-acrylamido-2-methylpropanesulfonate (AMPS), and positively charged (3-acryl-amidopropyltrimethylammonium chloride (APTAC) monomers were synthesized via conventional redox ini-tiated free radical copolymerization using N,N-methylenebis(acrylamide) (MBAA) as a cross-linking agent. The resulting nanogels were characterized by means of FTIR and 1H NMR spectroscopy, dynamic light scat-tering (DLS) and zeta-potential measurements. Surface morphology was analyzed using scanning electron microscopy. Due to the presence of thermally responsive NIPAM units and varying molar ratios of anionic (AMPS) and cationic (APTAC) units, the resulting nanogels were responsive to multiple stimuli in aqueous media and can be used for controlled delivery of dyes. Thus, the NIPAM90-APTAC7.5-AMPS2.5 nanogel with an excess of the cationic units was chosen for immobilization of the anionic dye, methyl orange (MO), whereas the NIPAM90-APTAC2.5-AMPS7.5 nanogel with an excess of the anionic units was chosen for immo-bilization of the cationic dye, methylene blue (MB). The release kinetics of the dyes from the nanogel was studied depending on the phase transition temperature and the salt content. Mechanism of the dye release from the nanogel matrix was determined using the Ritger-Peppas equation. Disappearance of the ionic con-tacts between the charged groups of the nanogels and the ionic dyes was suggested to be the main reason for the diffusion of the dyes through the dialysis membrane into the external solution.

Lowering the dimensionality of cationic lead bromide units in robust coordination polymers for enhanced self-trapped broadband emission

We report an organolead bromide hybrid consisting of 0D cationic bromoplumbate nodes that are connected by organocarboxylate linkers. The coordination structure affords both high chemical stability and enhanced structural strain for photoemission.

A sensitive zinc probe operating via enhancement of excited-state intramolecular charge transfer.

Novel highly sensitive fluorescent probes for zinc cations based on the diketopyrrolopyrrole scaffold were designed and synthesized. Large bathochromic shifts (≈80 nm) of fluorescence are observed when the Zn2+-recognition unit (di-(2-picolyl)amine) is bridged with the fluorophore possessing an additional pyridine unit able to participate in the coordination process. This effect originates from the dipolar architecture and the increasing electron-withdrawing properties of the diketopyrrolopyrrole core upon addition of the cation. The new, greenish-yellow emitting probes, which operate via modulation of intramolecular charge transfer, are very sensitive to the presence of Zn2+. Introduction of a morpholine unit in the diketopyrrolopyrrole structure induces a selective six-fold increase of the emission intensity upon zinc coordination. Importantly, the presence of other divalent biologically relevant metal cations has negligible effects and typically even at a 100-fold higher concentration of Mg2+/Zn2+, the effect is comparable. Computational studies rationalize the strong bathochromic shift upon Zn2+-complexation. Decorating the probes with the triphenylphosphonium cation and morpholine unit enables selective localization in the mitochondria and the lysosome of cardiac H9C2 cells, respectively.

Influence of Interaction between Organic Cation and Inorganic Unit in Bi-Based Hybrid Perovskites for Photoelectronic Properties

Influence of Interaction between Organic Cation and Inorganic Unit in Bi-Based Hybrid Perovskites for Photoelectronic Properties

Impact of counter anions on spin-state switching of manganese(III) complexes containing an azobenzene ligand.

Four mononuclear manganese(III) complexes coordinated with photo-active hexadentate azobenzene ligands, [Mn(5azo-sal2-323)](X) (X = Cl, 1; X = BF4, 2; X = ClO4, 3; X = PF6, 4), were prepared. The impact of various counter anions on the stabilization and switching of the spin state of the manganese(III) center was explored through detailed magneto-structural investigation using variable temperature single-crystal X-ray diffraction, magnetic, spectroscopic, and spectroelectrochemical studies, along with theoretical calculations. All four complexes consisted of an isostructural monocationic distorted octahedral MnN4O2 coordination environment offered by the hexadentate ligand and Cl-, BF4-, ClO4-, and PF6- as counter anions respectively. Complex 1 with a spherical Cl- counter anion showed a reversible and gradual spin-state switching between low-spin (LS) (S = 1) and high-spin (HS) (S = 2) states above 400 K, where non-covalent cation-anion interactions played a significant role in stabilizing the LS state. While, irrespective of the shape of the counter anion, complexes 2-4 remained in the HS state throughout the measured temperature range of 300-2 K, where strong π-π interaction between the azobenzene motifs among cationic units played a substantial role in stabilizing the HS state. Furthermore, magnetic data analyses revealed significantly large zero-field splitting in the S = 1 state for 1 (D = 19.4 cm-1, E/D = 0.008) in comparison with that in the S = 2 state for 2-4 (D = 3.99-4.97 cm-1, E/D = 0.002-0.195). Spectroelectrochemical investigations revealed the quasi-reversible reduction and oxidation of the manganese(III) center to manganese(II) and manganese(IV), respectively. A detailed theoretical calculation at the DFT and CASSCF level of theory was carried out to better understand the magneto-structural correlation.

Crystal structure of the dodecanuclear coordination compounds [

By slow hydrolysis of solutions of [Eu(DMF)8]I3 or [Nd(DMF)8]I3 in dimethylformamide (DMF), single crystals of the coordination compounds [RE12(DMF)24 (HCOO)8(OH)16]I3·4DMF (RE = Eu, Nd) were obtained. Both compounds crystallise isotypically in a tetragonal structure with space group I422 (No. 97, Z = 2, a = 21.881(3), 21.6340(10) and c = 20.873(2), 21.0612(9) Å for Nd and Eu compounds, respectively). The crystal structure shows a [RE12O56] core unit with O atoms from formate and hydroxide anions μ3-bridging the metal centres. The dodecanuclear cationic units are arranged in a body-centred packing topology, surrounded by iodide anions in a β cage pattern. Rietveld refinement confirmed the structure model, and the presence of hydroxide anions was shown by FT-IR spectroscopy. Susceptibility measurements on the Nd compound showed paramagnetic behaviour and a temperature dependence of μeff typical for trivalent Nd cations.

Alkaline Stability Evaluation of Polymerizable Hexyl-Tethered Ammonium Cations.

One of the important challenges in designing robust alkaline anion exchange membranes is the difficulty associated with the chemical stability of covalently bound cationic units. Here, a systematic study exploring alkaline stabilities of polymerizable hexyltrimethylammonium cations is presented, where the hexyl chain is linked to a phenyl ring through a direct carbon-carbon, phenyl ether, or benzyl ether functionality. For this work, small molecule model compounds, styrenic monomer analogs, and their homopolymers are synthesized. Alkaline stabilities of the small molecule cations and their homopolymers are compared to alkaline stability of benzyltrimethylammonium (BTMA) cation and its homopolymer poly(BTMA), respectively. All the hexyl-tethered cations and their homopolymers are significantly more stable under strongly alkaline conditions (2 m KOD at 80 °C). Moreover, ether-linked cations show comparable stability to the direct carbon-carbon linked cation. Via 1 H NMR analyses, possible degradation mechanisms are investigated for each small molecule cation. Findings of this study strongly suggest that the alkaline stability is dictated by the steric hindrance around the β-hydrogen. This study expands beyond the limits of general knowledge on alkaline stability of alkyl-tethered ammonium cations via the Hofmann elimination route, highlights important design parameters for stable ammonium cations, and demonstrates accessible directly polymerizable alkaline stable ammonium cations.

On the Supra-LUMO Interaction: Case Study of a Sudden Change of Electronic Structure as a Functional Emergence.

The synergistic functioning of redox-active components that emerges from prototypical 2,2'-di(N-methylpyrid-4-ylium)-1,1'-biphenyl is described. Interestingly, even if a trans conformation of the native assembly is expected, due to electrostatic repulsion between cationic pyridinium units, we demonstrate that cis conformation is equally energy-stabilized on account of a peculiar LUMO (SupLUMO) that develops through space, encompassing the two pyridiniums in a single, made-in-one-piece, electronic entity (superelectrophoric behavior). This SupLUMO emergence, with the cis species as superelectrophore embodiment, originates in a sudden change of electronic structure. This finding is substantiated by insights from solid state (single-crystal X-ray diffraction) and solution (NOE NMR and UV-vis-NIR spectroelectrochemistry) studies, combined with electronic structure computations. Electrochemistry shows that electron transfers are so strongly correlated that two-electron reduction manifests itself as a single-step process with a large potential inversion consistent with inner creation of a carbon-carbon bond (digital simulation). Besides, absence of reductive formation of dimers is a further indication of a preferential intramolecular reactivity determined by the SupLUMO interaction (cis isomer pre-organization). The redox-gated covalent bond, serving as electron reservoir, was studied via atropisomerism of the reduction product (VT NMR study). The overall picture derived from this in-depth study of 2,2'-di(N-methylpyrid-4-ylium)-1,1'-biphenyl proves that trans and cis species are worth considered as intrinsically sharply different, that is, as doubly-electrophoric and singly-superelectrophoric switchable assemblies, beyond conformational isomerism. Most importantly, the through-space-mediated SupLUMO may come in complement of other weak interactions encountered in Supramolecular Chemistry as a tool for the design of electroactive architectures.

Pb-Oxo Interactions in Uranyl Hybrid Materials: A Combined Experimental and Computational Analysis of Bonding and Spectroscopic Properties.

Reported are the syntheses and characterization of six new heterometallic UO22+/Pb2+ compounds. These materials feature rare instances of M-oxo interactions, which influence the bonding properties of the uranyl cation. The spectroscopic effects of these interactions were measured using luminescence and Raman spectroscopy. Computational density functional theory-based natural bonding orbital and quantum theory of atoms in molecules methods indicate interactions arise predominantly through charge transfer between cationic units via the electron-donating uranyl O spx lone pair orbitals and electron-accepting Pb2+ p orbitals. The interaction strength varies as a function of Pb-oxo interaction distance and angle with energy values ranging from 0.47 kcal/mol in the longer contacts to 21.94 kcal/mol in the shorter contacts. Uranyl units with stronger interactions at the oxo display an asymmetric bond weakening and a loss of covalent character in the U═O bonds interacting closely with the Pb2+ ion. Luminescence quenching is observed in cases in which strong Pb-oxo interactions are present and is accompanied by red-shifting of the uranyl symmetric Raman stretch. Changes to inner sphere uranyl bonding manifest as a weakening of the U═O bond as a result of interaction with the Pb2+ ion. Comprehensive evaluation of the effects of metal ions on uranyl spectra supports modeling efforts probing uranyl bonding and may inform applications such as forensic signatures.

Exploring phosphonium and ammonium chitosan polymers and their PEGylated analogs for high performance gene delivery

• New chitosan derivatives containing triethylammonium chloride or triethylphosphonium chloride and their PEGylated analogs have been synthesized and characterized. • The derivatives efficiently bind pDNA at low weight ratio of derivative:pDNA of 2.8:1. • Apoptosis measurements by flow cytometry indicated that the derivatives containing triethylammonium chloride or triethylphosphonium chloride and PEG induce no perceptible and mild apoptosis with their concentration at 100 µg/mL. • The present study provides evidence that these PEGylated derivatives are safe and effective vectors for efficient nucleic acid delivery. Among cationic polymers, chitosan (CS) is a promising non-viral vector due to its biocompatibility, biodegradability and safety profile. However, its application for gene delivery is hindered by its poor solubility at physiological pH. In this study, novel water-soluble chitosan derivatives containing triethylphosphonium chloride ((N-(1-carboxybutyl-4-triethylphosphonium chloride) chitosan = TEPB-CS)) or triethylammonium chloride ((N-(1-carboxybutyl-4-triethylammonium chloride) chitosan = TEAB-CS)) with 4-carbon spacers separating the cationic units from the chitosan backbone were synthesized by carbodiimide mediated coupling reactions. Two different degrees of substitution of quaternary phosphonium (43% and 21%) and ammonium (40.6% and 26%) were synthesized. The polymers with higher degrees of substitutions displayed higher solubility in aqueous media and were further grafted with mPEG (TEAB-CS-g-mPEG and TEPB-CS-g-mPEG) and used for DNA complexation, cytotoxicity, apoptosis, and gene transfection studies. Chemical characterization of the above polymers was performed by FTIR, 1 H NMR, and 31 P NMR, and the degree of substitution of the grafted phosphonium and ammonium and mPEG was calculated by 1 H NMR. The polymers efficiently bound pDNA at weight ratio of polymer:pDNA of 2.8:1. From dynamic light scattering experiments, the mean diameters of the calf thymus DNA complexes with the polymers, in water and phosphate buffer (pH 7.4), were in the range of 140 – 330 nm. Zeta potential of these complexes in water became positive as the weight ratios of the polymers/DNA exceeded 2:1. Most of these polymers mildly affect the viability of HeLa cells with a final concentration of 10 µg/mL or higher. Cell viability was only modestly compromised in the presence of 100 µg/mL of TEPB-CS-g-mPEG, and this derivative was also found to display the highest transfection efficiencies among all four polymers. Apoptosis measurements by flow cytometry indicated that both TEAB-CS-g-mPEG and TEPB-CS-g-mPEG induce no perceptible and mild apoptosis with their concentration at 100 µg/mL, respectively. Together, the present study provides evidence that these PEGylated TEPB-CS and TEAB-CS are safe and effective vectors for efficient nucleic acid delivery.

Umbelliferone Decorated Water-soluble Zinc(II) Phthalocyanines - In Vitro Phototoxic Antimicrobial Anti-cancer Agents.

In this contribution we report on the synthesis, characterization and application of water‐soluble zinc(II) phthalocyanines, which are decorated with four or eight umbelliferone moieties for photodynamic therapy (PDT). These compounds are linked peripherally to zinc(II) phthalocyanine by a triethylene glycol linker attached to pyridines, leading to cationic pyridinium units, able to increase the water solubility of the system. Beside their photophysical properties they were analyzed concerning their cellular distribution in human hepatocyte carcinoma (HepG2) cells as well as their phototoxicity towards HepG2 cells, Gram‐positive (S. aureus strain 3150/12 and B. subtilis strain DB104) and Gram‐negative bacteria (E. coli strain UTI89 and E. coli strain Nissle 1917). At low light doses and concentrations, they exhibit superb antimicrobial activity against Gram‐positive bacteria as well as anti‐tumor activity against HepG2. They are even capable to inactivate Gram‐negative bacteria, whereas the dark toxicity remains low. These unique water‐soluble compounds can be regarded as all‐in‐one type photosensitizers with broad applications ranges in the future.

Crystalline Hydrogen-Bonding Networks and Mixed-Metal Framework Materials Enabled by an Electronically Differentiated Heteroditopic Isocyanide/Carboxylate Linker Group.

Mixed-metal solid-state framework materials are emerging candidates for advanced applications in catalysis and chemical separations. Traditionally, the syntheses of mixed-metal framework systems rely on postsynthetic ion exchange, metalloligands, or metal-deposition techniques for the incorporation of a second metal within a framework material. However, these methods are often incompatible with the incorporation of low-valent metal centers, which preferentially bind to electronically "soft" ligands according to the tenets of hard/soft acid/base theory. Here we present the electronically differentiated isocyanide/carboxylate heteroditopic linker ligand 1,4-CNArMes2C6H4CO2H (TIBMes2H; TIB = terphenyl isocyanide benzoate; ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H2), which is capable of selective binding of low-valent metals via the isocyano group and complexation of hard Lewis acidic metals through the carboxylate unit. This heteroditopic ligand also possesses an encumbering m-terphenyl backbone at the isocyanide function to foster coordinative unsaturation. The treatment of TIBMes2H with [Cu(NCMe)4]PF6 in a 3:1 ratio results in preferential binding of the isocyanide group to the Cu(I) center as assayed by multinuclear NMR and IR spectroscopies. IR spectroscopy also provides strong evidence for the formation of a copper(I) tris(isocyanide) complex, wherein the carboxylic acid group remains unperturbed. The addition of TIBMes2 to [Cu(NCMe)4]PF6 in a 4:1 ratio results in crystallization of the hydrogen-bonding network, [Cu(TIBMes2H)4]PF6, in which the formation of R22(8) hydrogen bonds results in a 7-fold interpenetrated diamondoid lattice structure. The preassembly of a copper(I) tris(isocyanide) complex using TIBMes2H, followed by deprotonation and the introduction of ZnCl2, generates a novel and unusual zwitterionic solid-state phase (denoted as Cu/Zn-ISOCN-5; ISOCN = isocyanide coordination network) consisting of a coordinatively unsaturated [Cu(CNR)3]+ cationic secondary building unit (SBU) and an anionic, paddlewheel-type Zn(II)-based SBU of the formulation [Cl2Zn2(O2CR)3]-. Inductively coupled plasma mass spectrometry analysis provided firm evidence for a 2:1 Zn-to-Cu ratio in the network, thereby indicating that the isocyanide and carboxylate groups selectively bind soft and hard Lewis acidic metal centers, respectively. The extended structure of Cu/Zn-ISOCN-5 is a densely packed, noninterpenetrated AB-stacked layer network with modest surface area. However, it is thermally robust, and its formation and compositional integrity validate the use of an electronically differentiated linker for the formation of mixed-metal frameworks incorporating low-valent metal centers.

Facile Synthesis of Tetra-Branched Tetraimidazolium and Tetrapyrrolidinium Ionic Liquids.

A facile synthetic route for tetra-branched tetraimidazolium and tetrapyrrolidinium ionic liquids was developed. In contrast to the previous synthetic scheme, the new synthetic route requires only three reaction steps instead of seven. The total yield of tetracation was also improved from 17–21 to 39–41%. Using the new synthetic scheme, four kinds of tetracations were synthesized from the combination of two cationic units (imidazolium and pyrrolidinium) and two counteranions [bis(fluorosulfonyl)imide (FSI) and bis(trifluoromethanesulfonyl)imide (TFSI)]. Basic physical properties including glass transition temperature, thermal decomposition temperature, density, viscosity, and ionic conductivity were determined. The counterion exchange from TFSI to FSI resulted in lower glass transition temperature and higher ionic conductivity. Tetrapyrrolidinium exhibited higher viscosity and lower ionic conductivity than tetraimidazolium. The counterion exchange from TFSI to FSI resulted in lower viscosity in the case of tetraimidazolium, while the opposite result was obtained in the case of tetrapyrrolidinium. Tetracations composed of ethyl imidazolium units, diethylene glycol spacers, and FSI counterions exhibited the highest ionic conductivity of 3.5 × 10–4 S cm–1 at 25 °C under anhydrous conditions. This is the best ionic conductivity in the tetracations ever reported.