Structural Diversity in 2-(2-Aminoethyl)pyridine-Based Lead Iodide Hybrids.

While 2D metal-organic hybrids have emerged as promising solar absorbers due to their improved moisture stability, their inferior transport properties limit their potential translation into devices. We report a new hybrid containing 2-(2-ammonioethyl)pyridine [(2-AEP)+], forming a 2D hybrid with the composition (2-AEP)2PbI4. The organic bilayer comprises of (2-AEP)+, which is arranged in a face-to-face stacking that promotes π-π interactions between neighboring pyridyl rings. We also demonstrate the structural diversity of 2-(2-aminoethyl)pyridine-based lead iodide hybrids in solution-processed films. This report highlights the importance of solution-processing conditions in trying to obtain single-phase films of hybrids containing dibasic organic species.

Selective Generation of Aldimine and Ketimine Tautomers of the Schiff Base Condensates of Amino Acids with Imidazole Aldehydes or of Imidazole Methanamines with Pyruvates-Isomeric Control with 2- vs. 4-Substituted Imidazoles.

The Schiff base condensation of 5-methyl-4-imidazole carboxaldehyde, 5Me4ImCHO, and the anion of an amino acid, H2N-CH(R)CO2- (R = -CH3, -CH(CH3)2 and -CH2CH(CH3)2), gives the aldimine tautomer, Im-CH=N-CH(R)CO2-, while that of 5-methylimidazole-4-methanamine, 5MeIm-4-CH2NH2, with a 2-oxocarboxylate anion, R-C(O)-CO2-, gives the isomeric ketimine tautomer, Im-CH2-N=C(R)CO2-. All are isolated as the neutral nickel(II) complexes, NiL2, and are characterized by single crystal structure determination, IR, and positive ion ESI MS. In the cases of the 4 substituted imidazoles, either 5MeIm-4-CHO or 5MeIm-4-CH2NH2, both the aldimine and ketimine complexes are isolated cleanly with no evidence of an equilibrium between the two tautomers under the experimental conditions. The aldimines are blue while the tautomeric ketimines are green. In contrast, for the 2-substituted imidazoles, with either Im-2-CHO or Im-2-CH2NH2, the isolated product from the Schiff base condensation is the ketimine, which in the solid is green, as observed for the 4-isomer. These results suggest that for the 2-substituted imidazoles, there is a facile equilibrium between the aldimine and ketimine tautomers, and that the ketimine form is the thermodynamically favored tautomer. The aldimine tautomers of the 4-substituted imidazoles have three stereogenic centers, the nickel (Δ or Ʌ) and the two alpha carbon atoms (R or S). The observed pair of enantiomers is the ɅRR/ΔSS enantiomeric pair, suggesting that this pair is lower in energy than the others and that this is in general the preferred chiral correlation in these complexes.

Acyclic Cucurbit[n]uril Receptors Function as Solid State Sequestrants for Organic Micropollutants.

The accumulation of organic micropollutants (OMP) in aquatic systems is a major societal problem that can be addressed by approaches including nanofiltration, flocculation, reverse osmosis and adsorptive methods using insoluble materials (e.g. activated carbon, MOFs, nanocomposites). More recently, polymeric versions of supramolecular hosts (e.g. cyclodextrins, calixarenes, pillararenes) have been investigated as OMP sequestrants. Herein, we report our study of the use of water insoluble dimethylcatechol walled acyclic cucurbit[n]uril (CB[n]) hosts as solid state sequestrants for a panel of five OMPs. A series of hosts (H1-H4) were synthesized by reaction of glycoluril oligomer (monomer-tetramer) with 3,6-dimethylcatechol and fully characterized by spectroscopic means and x-ray crystallography. The solid hosts sequester OMPs from water with removal efficiencies exceeding 90 % in some cases. The removal efficiencies of the new hosts parallel the known molecular recognition properties of analogous water soluble acyclic CB[n]. OMP uptake by solid host occurs rapidly (≈120 seconds). Head-to-head comparison with CB[6] in batch-mode separation and DARCO activated carbon in flow-through separation mode show that tetramer derived host (H4) performs very well under identical conditions. The work establishes insoluble acyclic CB[n]-type receptors as a promising new platform for OMP sequestration.

Orbital Contribution to Paramagnetism and Noninnocent Thiophosphate Anions in Layered Li2MP2S6 Where M = Fe and Co.

Transition-metal thiophosphates and selenophosphates are layered systems with the potential for displaying two-dimensional (2D) magnetic phenomena. We present the crystal structures and magnetic properties of two lithium transition-metal thiophosphates, Li1.56Co0.71P2S6 and Li2.26Fe0.94P2S6. The previously unreported Li1.56Co0.71P2S6 crystallizes in the trigonal space group P31m with lattice parameters a = 6.0193(6) Å and c = 6.5675(9) Å. The CoS6 octahedra are arranged in a honeycomb lattice and form 2D layers separated by lithium cations. The previously solved Li2.26Fe0.94P2S6 is isostructural to Li1.56Co0.71P2S6 but displays site mixing between the Li+ and Fe2+ cations within the thiophosphate layer. Unusually, Li1.56Co0.71P2S6 appears to have P2S63- and not P2S64- anions. We therefore term it a "noninnocent" anion because of the ambiguous nature of its oxidation state. Combined neutron diffraction and magnetization measurements reveal that both Li1.56Co0.71P2S6 and Li2.26Fe0.94P2S6 display magnetic anisotropy as well as no long-range magnetic order down to 5 K. In the iron thiophosphate, susceptibility indicates an effective moment of 5.44(3) µB, which may be best described by an S + L model, where S = 2 and L = 2, or close to the free ion limit. In the cobalt thiophosphate, we found the effective moment to be 4.35(2) µB, which would point to an S = 3/2 and L = 1 model due to octahedral crystal-field splitting.

Contrasting Bonding Extremes in Two [Ge6]n- Complexes: A Wadian Polyhedron (n = 2) versus a Hydrocarbon-like 2c-2e Polygermanide (n = 12).

[Nb(η6-C6H3Me3)2] reacts with ethylenediamine (en) solutions of K4Ge9 in the presence of 18-crown-6 to give [(η6-C6H3Me3)NbHGe6]2- (1) and [(η6-C6H3Me3)NbGe6Nb(η6-C6H3Me3)]2- (2) as their corresponding [K(18-crown-6)]+ salts. The crystalline solids are dark brown, air-sensitive, and sparingly soluble or insoluble in most solvents. The [K(18-crown-6)]+ salts of cluster ions 1 and 2 have been characterized by energy-dispersive X-ray (EDX) analysis, NMR studies, single-crystal X-ray diffraction, and electrospray ionization time-of-flight (ESI-TOF) mass spectrometry studies. Cluster ions 1 and 2 have markedly different [Ge6] moieties: an electron-deficient carborane-like subunit in 1 and a two-center, two-electron cyclohexane-like subunit in 2.

Microwave-Assisted Synthesis of Organometallic Rhenium (I) Pentylcarbonato Complexes: New Synthon for Carboxylato, Sulfonato and Chlorido Complexes.

Tricarbonylrhenium(I)(α-diimine) complexes are of importance because of their strong cytotoxic and fluorescence properties. Syntheses of such complexes were achieved through a two-step process. First, the pentylcarbonato complexes, fac-(CO)3(α-diimine)ReOC(O)OC5H11 were synthesized through a microwave-assisted reaction of Re2(CO)10, α-diimine, 1-pentanol and CO2 in a few hours. Second, the pentylcarbonato complexes are treated with carboxylic, sulfonic and halo acids to obtain the corresponding carboxylato, sulfonato and halido complexes. This is the first example of conversion of Re2(CO)10 into a rhenium carbonyl complex through microwave-assisted reaction.

Acyclic Cucurbit[n]uril-Type Receptors: Aromatic Wall Extension Enhances Binding Affinity, Delivers Helical Chirality, and Enables Fluorescence Sensing.

We report the linear extension from M1 to M2 to anthracene walled M3 which adopts a helical conformation (X-ray) to avoid unfavorable interactions between sidewalls. M3 is water soluble (=30 mm) and displays enhanced optical properties (ϵ=1.28×105 m-1 cm-1 , λmax =370 nm) relative to M2. The binding properties of M3 toward guests 1-29 were examined by 1 H NMR and ITC. The M3⋅guest complexes are stronger than the analogous complexes of M2 and M1. The enhanced binding of M3 toward neuromuscular blockers 25, 27-29 suggests that M3 holds significant promise as an in vivo reversal agent. The changes in fluorescence observed for M3⋅guest complexes are a function of the relative orientation of the anthracene sidewalls, guest concentration, Ka , and guest electronics which rendered M3 a superb component of a fluorescence sensing array. The work establishes M3 as a next generation sequestering agent and a versatile component of fluorescence sensors.

Endohedral Plumbaspherenes of the Group 9 Metals: Synthesis, Structure and Properties of the [M@Pb12 ]3- (M=Co, Rh, Ir) Ions.

The icosahedral [M@Pb12 ]3- (M=Co(1), Rh(2), Ir(3)) cluster ions were prepared from K4 Pb9 and Co(dppe)Cl2 (dppe=1,2-bis(diphenylphosphino)ethane)/[Rh(PPh3 )3 Cl]/[Ir(cod)Cl]2 (cod=1,5-cyclooctadiene), respectively, in the presence of 18-crown-6/ 2,2,2-cryptand in ethylenediamine/toluene solvent mixtures. The [K(2,2,2-cryptand)]+ salt of 1 and the [K(18-crown-6)]+ salt of 3 were characterized via X-ray crystallography; the ions 1 and 3 are isostructural and isoelectronic to the [Rh@Pb12 ]3- (2) ion as well as to the group 10 clusters [M'@Pb12 ]2- (M'=Ni, Pd, Pt). The ions are all 26-electron clusters with near perfect icosahedral Ih point symmetry. Clusters 1-3 show record downfield 207 Pb NMR chemical shifts due to σ-aromaticity of the cluster framework. Calculated and observed 207 Pb NMR chemical shifts and 207 Pb-x M J-couplings (x M=59 Co, 103 Rh, 193 Ir) are in excellent agreement and DFT analysis shows that the variations of 207 Pb NMR chemical shifts for the [M@Pb12 ]2, 3- ions (M=Co, Rh, Ir, Ni, Pd, Pt) are mainly governed by the perpendicularly oriented σ11 component of the chemical shift anisotropy tensor. The laser desorption ionization time-of-flight (LDI-TOF) mass spectra contain the molecular ions as well as several new gas phase clusters derived from the parents. The DFT-minimized structures of these ions are described.

Pillar[n]MaxQ: A New High Affinity Host Family for Sequestration in Water.

We report the synthesis, X-ray crystal structure, and molecular recognition properties of pillar[n]arene derivative P[6]AS, which we refer to as Pillar[6]MaxQ along with analogues P[5]AS and P[7]AS toward guests 1-18. The ultratight binding affinity of P[5]AS and P[6]AS toward quaternary (di)ammonium ions renders them prime candidates for in vitro and in vivo non-covalent bioconjugation, for imaging and delivery applications, and as in vivo sequestration agents.

An Electron-Poor Dioxa-[2.1.1]-(2,6)-pyridinophane Ligand and Its Application in Cu-Catalyzed Olefin Aziridination.

A novel macrocyclic 1,7-dioxa-[2.1.1]-(2,6)-pyridinophane ligand has been synthesized and crystallographically characterized. Two derived metal complexes, dichloropalladium(II) and chlorocopper(I), were prepared. In the palladium(II) complex LPdCl2, both in the solid state, according to its crystallographic characterization, and in CH2Cl2 solutions at -40 °C, according to 1H NMR spectroscopy, the ligand adapts a C1-symmetric κ2-N,N-coordination mode in which the metal atom binds to two nonequivalent pyridine fragments of the macrocycle. The complex is fluxional at 20 °C. In the crystalline copper(I) complex LCuCl, the macrocyclic ligand is also κ2-N,N-coordinated to the metal, but it utilizes two equivalent pyridine fragments for the binding. The copper(I) complex is fluxional in CH2Cl2 solutions in the temperature range between 20 and -70 °C and is proposed to be involved in a fast intermolecular macrocyclic ligand exchange which is slowed down below -40 °C. DFT calculations predict a lower thermodynamic stability of the dioxapyridinophane-derived complexes LPdCl2 and LCuCl, as compared to their [2.1.1]-(2,6)-pyridinophane analogs containing bridging CH2 groups instead of the oxygen atoms. The electron poor dioxapyridinophane chlorocopper(I) complex, in combination with NaBArF4 (BArF4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) in dichloromethane solutions, can serve as an efficient catalyst for aziridination of various olefins with PhINTs at 0-22 °C.

Synthesis and Characterization of the {Si(NHCH2CH2NH)3[Mo(CO)3]2}2- Complex Comprising the Si(NHCH2CH2NH)32- Octahedron.

Reactions of K12Si17 with the low-valent transition-metal complex Mo(CO)3(C7H8) in ethylenediamine/toluene solutions in the presence of 2,2,2-cryptand yield the {Si(NHCH2CH2NH)3[Mo(CO)3]2}2- dianion, which contains an octahedral Si(NHCH2CH2NH)32- subunit. The SiN6 core comprises a rare example of a doubly deprotonated ethylenediame ligand in a coordination complex and is also the first structurally characterized example of a homoleptic Si(N∩N)3 trischelate. Its structure and spectroscopic properties are described.

Triazole functionalized acyclic cucurbit[n]uril-type receptors: host·guest recognition properties.

We report the synthesis of three new triazole functionalized acyclic CB[n]-type receptors (2-4) by click chemistry. The compounds have good solubility in water (≥8 mM) and do not undergo strong self-association (Ks ≤ 903 M-1). We measured the binding constants of 2-4 toward guests 9-24 and compared the results to those obtained for the prototypical acyclic CB[n]-type receptor 1. The X-ray crystal structure of 4 is also described.

Acyclic Cucurbit[n]uril Type Receptors: Secondary Versus Tertiary Amide Arms.

Two acyclic CB[n]-type hosts (1 and 2) which possess four 2° or 3° amide arms are reported; 1 and 2 are slightly soluble in water and do not self-associate. Host 2 has four 3° amide arms that exist as a mixture of E- and Z-isomers. 1H NMR was used to qualitatively investigate the binding properties of 1 and 2 which indicates they retain the essential binding features of macrocyclic CB[n] hosts (e.g. cavity binding of hydrophobic residues and portal binding of cationic groups). We measured the Ka values of 1 and 2 toward guests 6 - 12, methamphetamine, and fentanyl by ITC to evaluate their potential as in vivo sequestration agents. Neutral hosts 1 and 2 bind less tightly than tetraanionic hosts M1, ACB1, and ACB2. We attribute the lower Ka values to the absence of secondary ion-ion (ammonium•••sulfonate or ammonium•••carboxylate) electrostatic interactions for host•guest complexes of 1 and 2. The secondary amide functionality on 1 decreases affinity by formation of intramolecular NH•••O=C H-bonds. Tertiary amide host 2 binds even more weakly than 1 due to backfolding of the amide N-CH3-groups of 2 into its own cavity. The x-ray crystal structure of 2 supports this conclusion.

Drawing with Iron on a Gel Containing a Supramolecular Siderophore.

Guanosine-5'-hydroxamic acid (3) forms hydrogels when mixed with guanosine (1) and KCl. The 5'-hydroxamic acid (HA) unit is pH-responsive and also chelates Fe3+ . When gels are prepared under basic conditions, the 5'-HA groups are deprotonated and the anionic hydrogel binds cationic thiazole orange (TO), signaled by enhanced fluorescence. The HA nucleoside 3, when immobilized in the G-quartet gel, acts as a supramolecular siderophore to form red complexes with Fe3+ . We patterned the hydrogel's surface with FeCl3 , by hand and by using a 3D printer. Patterns form instantly, are visible by eye, and can be erased using vitamin C. This hydrogel, combining self-assembled G-quartet and siderophore-Fe3+ motifs, is strong, can be molded into different shapes, and is stable on the bench or under salt water.

Hybrid Molecular Container Based on Glycoluril and Triptycene: Synthesis, Binding Properties, and Triggered Release.

We designed and synthesized a "hybrid" molecular container 1, which is structurally related to both cucurbit[n]uril (CB[n]) and pillar[n]arene type receptors. Receptor 1 was fully characterized by 1 H NMR, 13 C NMR, IR, MS and X-ray single crystal diffraction. The self-association behavior, host-guest recognition properties of 1, and the [salt] dependence of Ka were investigated in detail by 1 H NMR and isothermal titration calorimetry (ITC). Optical transmittance and TEM measurements provide strong evidence that receptor 1 undergoes co-assemble with amphiphilic guest C10 in water to form supramolecular bilayer vesicles (diameter 25.6±2.7 nm, wall thickness ≈3.5 nm) that can encapsulate the hydrophilic anticancer drug doxorubicin (DOX) and the hydrophobic dye Nile red (NR). The release of encapsulated DOX or NR from the vesicles can be triggered by hexamethonium (8 c) or spermine (10) which leads to the disruption of the supramolecular vesicles.

Unprecedented anticancer activities of organorhenium sulfonato and carboxylato complexes against hormone-dependent MCF-7 and hormone-independent triple-negative MDA-MB-231 breast cancer cells.

Cisplatin and other metal-based drugs often display side effects and tumor resistance after prolonged use. Because rhenium-based anticancer complexes are often less toxic, a novel series of organorhenium complexes were synthesized of the types: XRe(CO)3Z (X = α-diimines and Z = p-toluenesulfonate, 1-naphthalenesulfonate, 2-naphthalenesulfonate, picolinate, nicotinate, aspirinate, naproxenate, flufenamate, ibuprofenate, mefenamate, tolfenamate, N-acetyl-tryptophanate), and their biological properties were examined. Specifically, in hormone-dependent MCF-7 and hormone-independent triple-negative MDA-MB-231 breast cancer cells, the p-toluenesulfonato, 1-naphthalenesulfonato, 2-naphthalenesulfonato, picolinato, nicotinato, acetylsalicylato, flufenamato, ibuprofenato, mefenamato, and N-acetyl-tryptophanato complexes were found to be far more potent than conventional drug cisplatin. DNA-binding studies were performed in each case via UV-Vis titrations, cyclic voltammetry, gel electrophoresis, and viscosity, which suggest DNA partial intercalation interaction, and the structure-activity relationship studies suggest that the anticancer activities increase with the increasing lipophilicities of the compounds, roughly consistent with their DNA-binding activities.

Blurring the Lines between Host and Guest: A Chimeric Receptor Derived from Cucurbituril and Triptycene.

We report the synthesis and X-ray crystal structure of a cucurbituril-triptycene chimeric receptor (1). Host 1 binds to guests typical of CB[6]-CB[8], but also binds to larger guests such as blue box (20) and the Fujita square (22). Intriguingly, the geometries of the 1⋅20 and 1⋅22 complexes blur the lines between host and guest in that both components fulfill both roles within each complex. The fluorescence output of 1 is fully quenched by the formation of complexes with pyridinium-derived guests.

Templating and Catalyzing [2+2] Photocycloaddition in Solution Using a Dynamic G-Quadruplex.

We describe a templating/covalent capture strategy that enables photochemical formation of 8 cyclobutanes in one noncovalent assembly. This process was characterized by experiment and quantum mechanical/molecular mechanics (ONIOM) calculations. Thus, KI and 16 units of 5'-cinnamate guanosine form a G-quadruplex where C=C π bonds in neighboring G4 -quartets are separated by 3.3 Å, enabling [2+2] photocycloaddition in solution. This reaction is high-yielding (>90 %), regio- and diastereoselective. Since all components are in dynamic equilibrium this photocycloaddition is catalytic in K+ .

Reductive C(sp2)-N Elimination from Isolated Pd(IV) Amido Aryl Complexes Prepared Using H2O2 as Oxidant.

Di-2-pyridyl ketone (dpk)-supported amidoarylpallada(II)cycles derived from various 2-(N-R-amino)biphenyls (R = H, Me, CF3CO, MeSO2, CF3SO2) react with hydrogen peroxide in MeOH, THF, MeCN or AcOH to form the corresponding C-N coupled products, N-R-substituted carbazoles, in 82-98% yield. For R = MeSO2 and CF3SO2, the corresponding reaction intermediates, amidoaryl Pd(IV) complexes were isolated and characterized by single crystal X-ray diffraction and/or NMR spectroscopy. For the first time, the C(sp2)-N reductive elimination from isolated amidoaryl Pd(IV) complexes has been studied in detail.

Supramolecular Sensors for Opiates and Their Metabolites.

The present study highlights a sensing approach for opiates using acyclic cucurbituril (aCBs) sensors comprising four glycouril units terminated on both ends with naphthalene fluorophore walls. The connectivity between the glycourils and naphthalene rings largely defines the opening size of the cucurbituril cavity and its diameter. The large hydrophobic binding cavity is flexible and is able to adapt to guests of various size and topology. The recognition event between the aCBs and guests results in modification of the fluorescence of the terminal walls, a fluorescence response that can be used to sense the drugs of abuse morphine, heroin, and oxycodone as well as their metabolites. Molecular dynamics is employed to understand the nature of the binding interactions. A simple three sensor cross-reactive array enables the determination of drugs and their metabolites in water with high fidelity and low error. Quantitative experiments performed in urine using a new three-way calibration model allows for determination of drugs and their metabolites using one sensor from a single fluorescence reading.