Ternary Complexes of BiI3/CuI and SbI3/CuI with Tetrahydrothiophene.

Reactions of BiI3/CuI mixtures with tetrahydrothiophene (THT) in toluene produce 2-D sheet networks BiCu3I6(THT)n (n = 2, 3, or 4), depending on reaction conditions. All three structures are based on BiI6 octahedra, which share pairs of (µ2-I)2 with Cu3(THT)n units. BiCu3I6(THT)2 features Cu2(µ2-I)2 rhombs with close Cu···Cu interactions and is accompanied by formation of the very complex HBi3Cu12I22(THT)8. Reactions of SbI3/CuI with THT in toluene produced a SbCu3I6(THT)2 network shows Cu3(µ2-THT)2 units, like its Bi congener, but Cu6(µ2-I)6 barrels rather than rhombs. Isolated SbI3 units are stacked above the Cu6I6 barrels. A molecular compound, Sb3Cu3I12(THT)6 consists of a face-sharing Sb3I12 stack, in which the Cu-THT units are bonded in asymmetric fashion about the central SbI6. Metal-halide bonds were investigated via QTAIM and NLMO analyses, demonstrating that these bonds are largely ionic and occur between the Bi/Sb and I p orbitals. Hirshfeld analysis shows significant H···H and H···I interactions. Diffuse reflectance spectroscopy (DRS) reveals band edges for the Bi species of 1.71-1.82 eV, while those for the neutral Sb complexes are in the range of 1.94-2.06 eV. Mapping of the electronic structure via density of state calculations indicates population of antibonding Bi/Sb-I orbitals in the excited state.

Crystal structure and Hirshfeld surface analysis of cyclo-tetra-bromido-1κ2Br,3κ2Br-tetra-kis-(µ2-2-{[(pyridin-2-yl)meth-yl]amino}-ethane-1-thiol-ato-κ3N,S:S)tetra-mercury(II).

The macrometallacyclic title compound, [Hg4Br4(C8H11N2S)4] or [((HgL 2)(HgBr2))2] (1) where HL = 2-{[(pyridin-2-yl)meth-yl]amino}-ethane-1-thiol, was prepared and structurally characterized. The Hg2+ complex crystallizes in the P21/c space group. The centrosymmetric Hg4S4 metallacycle is constructed from metal ions with alternating distorted tetra-hedral Br2S2 and distorted seesaw N2S2 primary coordination environments with pendant pyridyl groups. The backfolded extended chair metallacycle conformation suggests inter-actions between each of the bis-chelated mercury atoms and Br atoms lying above and below the central Hg2S4 plane. Supra-molecular inter-actions in 1 include a fourfold aryl embrace and potential hydrogen bonds with bromine as the acceptor. Hirshfeld surface analysis indicates that H⋯H (51.7%), Br⋯H/H⋯Br (23.0%) and C⋯H/H⋯C (9.5%) inter-actions are dominant.

Rapid single crystal growth via guest displacement from host-guest complexes.

The preparation of single crystals of sparingly soluble polycyclic aromatic compounds in MeCN is facilitated by solubilizing ionic host-guest complexation under otherwise poor solvent conditions. The guest is then crystallized within minutes through controlled guest displacement from the host via competitor equilibria, or over days through direct crystallization of the host-guest complex itself.

Homo- and Heteronuclear Group 12 Metallothionein Type B Cluster Analogs: Synthesis, Structure, 1H NMR and ESI-MS.

Metallothioneins (MTs) are a ubiquitous class of small cysteine-rich metal-binding proteins involved in metal homeostasis and detoxification with highly versatile metal binding properties. Despite the long-standing association of MT with M3S3 and M4S5 metal clusters, synthetic complexes with these core architectures are exceptionally rare. Here, we demonstrate an approach to synthesizing and characterizing aggregates of group 12 metal ions with monocyclic M3S3 cores in acetonitrile solution without the protection of a protein. Multidentate monothiol ligand N,N-bis(2-pyridylmethyl)-2-aminoethanethiol (L1H) provided [Cd3(L1)3](ClO4)3 (1), the first structurally characterized nonproteinaceous aggregate with a metallothionein-like monocyclic Cd3S3 core. In addition, [Zn3(L1)3](ClO4)3·4CH3CN (2·4CH3CN) was characterized by X-ray crystallography. The complex cations of 1 and 2 had comparable structures despite being nonisomorphic. Variable temperature and concentration 1H NMR were used to investigate aggregation equilibria of 1, 2, and a precipitate with composition "Hg(L1)(ClO4)" (3). Cryogenic 1H NMR studies of 3 revealed a J(199Hg1H) coupling constant pattern consistent with an aggregate possessing a cyclic core. ESI-MS was used for gas-phase characterization of 1-3, as well as mixed-metal [M2M'(L1)3(ClO4)2]+ ions prepared in situ by pairwise acetonitrile solution combinations of the group 12 complexes of L1. Access to synthetic variants of metallothionein-like group 12 aggregates provides an additional approach to understanding their behavior.

Pyridine interaction with γ-CuI: synergy between molecular dynamics and molecular orbital approaches to molecule/surface interactions.

We have used a synergistic computational approach merging Molecular Dynamics (MD) simulations with density functional theory (DFT) to investigate the mechanistic aspects of chemisorption of pyridine (Py) molecules on copper iodide. The presence of both positive and negative ions at the metal halide surface presents a chemical environment in which pyridine molecules may act as charge donors and/or acceptors. Computational results reveal that Py molecules interact with the γ-CuI(111) surface owing to a combination of noncovalent Cu⋯N, Cu/I⋯π/π*, and hydrogen bonding interactions as determined via Natural Bonding Orbitals (NBO). Introduction of surface defect sites alters the interaction dynamics, resulting in a "localizing effect" in which the Py molecules clump together within the defect site. Significant enhancement of hydrogen bonding between C-H σ* and I 6p orbitals results in more tightly surface-bound Py molecules. Our findings provide a platform for understanding the interaction between Py and Py-derivative vapors and metal-based surfaces that contain both electron acceptor and donor atoms.

Understanding the vapochromic response of mixed copper(i) iodide/silver(i) Iodide nanoparticles toward dimethyl sulfide.

We report on the vapochromic behavior of a series of homo- and heterometallic copper(i) iodide/silver(i) iodide nanoparticles when exposed to dimethyl sulfide (DMS) vapor. These systems show remarkable colorimetric sensing behavior via emission color upon DMS exposure, shifting from pink to green emission. Kinetics measurements of CuI/AgI nanoparticle reactions with DMS show a significant rate increase with increasing Ag(i) content. However, luminescence spectroscopy and X-ray diffraction of the post-exposure samples with varying Ag(i) content reveal that the luminophore is identical in all cases and contains no Ag(i) ions. To rationalize the experimental observations and determine the vapochromic response mechanism, molecular dynamic calculations were performed on model (111) cation-terminated surfaces of copper iodide crystals doped with variable amounts of silver. Computational studies indicate that heterometallic Cu/Ag systems have a stronger binding affinity towards DMS vapor molecules than homometallic CuI and that embedding of the DMS molecules into the surface is the primary intermediate by which the vapochromic response occurs.

Alkyl pyridinium iodocyanocuprate(i) chains (RPy)2[Cu2I3(CN)]: insight into structural, electronic and spectroscopic properties.

Equimolar mixtures of copper(i) iodide (CuI) and copper(i) cyanide (CuCN) react with N-alkyl pyridinium iodides (RPy+I-, R = Me, Et, n-propyl = Pr, and n-butyl = Bu) to produce pyridinium iodocyanocuprate(i) salts, (RPy)2[Cu2I3CN]. Crystal structures reveal isostructural anionic chains consisting of trigonal pyramidal Cu2(µ2-I)3 clusters bridged by C/N-disordered cyano units. The 1-D chains are nearly linear but vary with respect to whether adjacent clusters are staggered or eclipsed. A detailed investigation via Hirshfeld surface analysis reveals that hydrogen bonding between the triiodide group and pyridinium cation are the driver for assembly in these systems. Interestingly, spectroscopic investigations of absorption edge and emission energies show a general red shift with increasing hydrogen bonding. DFT and TD-DFT calculations were used to determine the electronic structure and band assignment of these materials to elucidate the nature behind this structure/function relationship.

Mild, Modular, and Convergent Synthesis of Helical Naphtho[2,1-c]chromenes via a Multistep Cyclization/Aromatization Cascade Sequence.

Tetracyclic 6H-naphtho[2,1-c]chromenes are expeditiously synthesized through a BF3·OEt2-mediated, three-step cascade reaction, creating new central pyran and aromatic rings. The cascade involves the addition of phenol-derived alkynyl substrates to BF3-activated aldehydes followed by alkyne-Prins cyclization, Friedel-Crafts reaction, and final elimination. Aliphatic and electron-deficient aromatic aldehydes afford the products in 50-74% isolated yields, but benzaldehyde and tolualdehyde resulted in lower yields. X-ray analysis of a p-bromophenyl derivative (5aA) shows the two aromatic moieties are twisted by 28° to create a helical backbone.

Synthesis and Luminescence of Optical Memory Active Tetramethylammonium Cyanocuprate(I) 3D Networks.

The structures of three tetramethylammonium cyanocuprate(I) 3D networks [NMe4]2[Cu(CN)2]2•0.25H2O (1), [NMe4][Cu3(CN)4] (2), and [NMe4][Cu2(CN)3] (3), (Me4N = tetramethylammonium), and the photophysics of 1 and 2 are reported. These complexes are prepared by combining aqueous solutions of the simple salts tetramethylammonium chloride and potassium dicyanocuprate. Single-crystal X-ray diffraction analysis of complex 1 reveals {Cu2(CN)2(µ2-CN)4} rhomboids crosslinked by cyano ligands and D3h {Cu(CN)3} metal clusters into a 3D coordination polymer, while 2 features independent 2D layers of fused hexagonal {Cu8(CN)8} rings where two Cu(I) centers reside in a linear C∞v coordination sphere. Metallophilic interactions are observed in 1 as close Cu⋯Cu distances, but are noticeably absent in 2. Complex 3 is a simple honeycomb sheet composed of trigonal planar Cu(I) centers with no Cu…Cu interactions. Temperature and time-dependent luminescence of 1 and 2 have been performed between 298 K and 78 K and demonstrate that 1 is a dual singlet/triplet emitter at low temperatures while 2 is a triplet-only emitter. DFT and TD-DFT calculations were used to help interpret the experimental findings. Optical memory experiments show that 1 and 2 are both optical memory active. These complexes undergo a reduction of emission intensity upon laser irradiation at 255 nm although this loss is much faster in 2. The loss of emission intensity is reversible in both cases by applying heat to the sample. We propose a light-induced electron transfer mechanism for the optical memory behavior observed.

Synthesis of Spirocyclic Diphosphite-Supported Gold Metallomacrocycles via a Protodeauration/Cyclization Strategy: Mechanistic and Binding Studies.

A spirocylic diphosphite was used to generate P-metalated bimetallic complexes through protodeauration reactions involving LAuC6H4tBu (L = JohnPhos, tBuXPhos) and metallomacrocycles through protodeauration/cyclization using tBuC6H4AuP^PAuC6H4tBu precursors (P^P = flexible diphosphine). While the synthesis of the bimetallic complexes followed a stepwise process, generation of the metallomacrocycles was highly complex because of a series of reversible ligand redistribution reactions. The self-assembly was monitored, and key intermediates were identified by NMR spectroscopy and high-resolution mass spectrometry. The mechanistic investigation showed that using flexible diphosphine linkers was critical to the selective synthesis of metallomacrocycles because rigid diphosphines generated intractable mixtures of linear and cyclic compounds. The X-ray structure of a 32-membered metallomacrocycle revealed that the compound crystallized in an unsymmetrical collapsed form that was held together by two supported aurophilic interactions while the flexible diphosphines were folded along opposite sides of the metallomacrocycle. The solution structure was consistent with a symmetric species, which suggested interconversion between an open and collapsed form and/or rapid twisting of a collapsed form. The 32-membered metallomacrocycle was used to bind estrogen primarily through the formation of AuP-O-···H-OR hydrogen bonds.

Alkyl Pyridinium Iodocuprate(I) Clusters: Structural Types and Charge Transfer Behavior.

The reaction of copper(I) iodide (CuI) and N-alkyl pyridinium (RPy+, R = H, Me, Et, n-propyl = Pr, n-butyl = Bu, n-pentyl = Pn, and n-hexyl = Hx) or N-butyl-3-substituted pyridinium (N-Bu-3-PyX+, X = I, Br, Cl, CN, and OMe) iodide salts yielded pyridinium iodocuprate(I) salts. Crystal structures of iodocuprate ions coupled with RPy+ include {Cu3I6 3-} n (R = H), {Cu2I3 -} n (R = Me), {Cu3I4 -} n (R = Et), {Cu6I8 2-} n (R = Pr), and {Cu5I7 2-} n (R = Bu, Pn, Hx). The [N-Bu-3-PyX]+ ions were typically paired with the 1-D chain {Cu5I7 2-} n . Diffuse reflectance spectroscopy performed on the [N-Bu-3-PyX]+ iodocuprate salts revealed that increasing the electron withdrawing capacity of the [N-Bu-3-PyX]+ system reduced the absorption edge of the iodocuprate salt. Variable temperature emission spectra of several [N-Bu-3-PyX]+ compounds revealed two emission peaks, one consistent with a cluster-centered halide to metal charge transfer and the other consistent with an intermolecular mixed halide/metal charge transfer to the organic cation. The emission intensity and emission wavelength of the mixed halide/metal to cation charge transfer depends on the organic cation substitution.

Further Investigation of the Intermolecular Diels-Alder Cycloaddition for the Synthesis of Bicyclo[2.2.2]diazaoctane Alkaloids.

The convergent synthesis of bicyclo[2.2.2]diazaoctane structures using an intermolecular Diels-Alder cycloaddition between a pyrazinone and commercially available fumarate or maleate precursors is reported. High reactivity and stereoselection is observed with both dienophile substrates. Structure validation was achieved by conversion of cycloadducts into known [2.2.2]diazabicyclic compounds or into crystalline derivatives suitable for X-ray analysis. The cycloadduct derived from reaction of pyrazinone and maleic anhydride underwent selective anhydride ring opening and intersected an established precursor in the synthesis of brevianamide B.

Electrophilic Cyclization of Phenylalkynediols to Naphthyl(aryl)iodonium Triflates with Chelating Hydroxyls: Preparation and X-ray Analyses.

Alkynediols containing one propargylic alcohol as well as a second alcohol, which is propargylic or homopropargylic, react with PhI+CN-OTf (Stang's reagent) or 3,5-(CF3)2C6H3I+CN-OTf to afford naphthyl(aryl)iodonium triflates. The reaction occurs at room temperature over the course of 6-12 h and provides 36-82% yields of microcrystalline solids. Slow diffusion of Et2O into CH3CN solutions of the salts afforded X-ray quality crystals of five compounds with hydroxyl groups forming five- and six-membered chelation complexes with the iodine atom. Crystallizations from larger scale reactions (≥∼0.25 mmol) were generally facile from CH2Cl2.

Metal Substitution and Solvomorphism in Alkylthiolate-Bridged Zn3 and HgZn2 Metal Clusters.

The impact of substituting Hg(II) for Zn(II) in a thiolate-bridged trinuclear cluster with parallels to a metallothionein metal cluster was investigated. A new solvomorph of [Zn(ZnL)2](ClO4)2 (1) (L = N-(2-pyridylmethyl)-N-(2-(ethylthiolato)-amine) and five solvomorphs of a new compound [Hg(ZnL)2](ClO4)2 (2) were characterized by single-crystal X-ray crystallography. The interplay of hydrogen bonding and aromatic-packing interactions in producing lamellar, 2D lamellar, and columnar arrangements of complex cations in the crystalline state is discussed. Both variable temperature proton nuclear magnetic resonance and electrospray ion-mass spectrometry (ESI-MS) suggest that the complex ions of 1 and 2 are the predominant solution species at moderate concentrations. ESI-MS was also used to monitor differences in metal ion redistribution as 1 was titrated with Hg(ClO4)2 and [HgL(ClO4)]. These studies document the facile replacement of Zn(II) by Hg(II) with the preservation of the overall structure in thiolate-rich clusters.

Contrasting coordination behavior of Group 12 perchlorate salts with an acyclic N3O2 donor ligand by X-ray crystallography and (1)H NMR.

An unbranched N3O2 ligand 2,6-bis[((2-pyridinylmethyl)oxy)methyl]pyridine (L1) was used to prepare new mononuclear heteroleptic Group 12 perchlorate complexes characterized by IR, (1)H NMR and X-ray crystallography. Racemic complexes with pentadentate L1 and one to four oxygens from either water or perchlorate bound to a metal ion were structurally characterized. Octahedral [Zn(L1)(OH2)](ClO4)2 (1) and pentagonal bipyramidal [Cd(L1)(OH2)(OClO3)]ClO4 (2) structures were found with lighter congeners. The polymorphic forms of [Hg(L1)(ClO4)2] characterized (3 in P1[combining macron] and 4 in P21/c) had a mix of monodentate, anisobidentate and bidentate perchlorates, providing the first examples of a tricapped trigonal prismatic Hg(ii) coordination geometry, as well as additional examples of a rare square antiprismatic Hg(ii) coordination geometry. Solution state (1)H NMR characterization of the Group 12 complexes in CD3CN indicated intramolecular reorganization remained rapid under conditions where intermolecular M-L1 exchange was slow on the chemical shift time scale for Zn(ii) and on the J(M(1)H) time scale for Cd(ii) and Hg(ii). Solution studies with more than one equivalent of ligand also suggested that a complex with a 1 : 2 ratio of M : L1 contributed significantly to solution equilibria with Hg(ii) but not the other metal ions. The behavior of related linear pentadentate ligands with Group 12 perchlorate salts is discussed.

Bis-tetradentate complexes of Cd(II) and Hg(II) with N8 coordination: structural and NMR comparisons.

Tripodal N4 ligands tris[(1-methylimidazol-2-yl)methyl]amine (L1), bis[(1-methylimidazol-2-yl)methyl][(2-pyridyl)methyl]amine (L2) and [(1-methylimidazol-2-yl)methyl]-bis-[(2-pyridyl)methyl]amine (L3) were used to prepare five new [ML2](ClO4)2 (M = Cd(II), Hg(II)) complexes. All complexes had N8 metal coordination and a trans-bicapped octahedral structure as determined by X-ray crystallography. Metal-nitrogen bond distances generally decreased in the order M-Namine > M-Npyridyl > M-Nimidazoyl, and the perchlorates were well separated from the metal ions. Variable temperature solution state (1)H NMR spectroscopy revealed conditions for slow intramolecular reorganization were more readily accessible for the Cd(II) complexes than for the Hg(II) complexes. Both protons of imidazoyl ring ligand components had large, comparable J((199)Hg(1)H) despite sizable differences in nuclear separation.

Photophysical properties of {[Ag(CN)2](-)}2 complexes trapped in a supramolecular electron-acceptor organic framework.

The organic acceptor 1,1'-bis-(2,4-dinitrophenyl)-4,4'-bipyridinium (DNP(2+)) reacts with dicyanoargentate to form a supramolecular complex with the general formula: {[Ag(CN)2]2DNP}·2H2O. The photophysical properties of this complex were determined using solid-state luminescence experiments including luminescence lifetime measurements. Luminescence of the dicyanoargentate dimers is observed both by direct excitation of the silver dimers as well as excitation of the DNP(2+) followed by indirect non-radiative energy transfer to the silver dimer units for emission. The structures themselves were characterized using X-ray crystallography. The results are compared to those from the previously studied {[Au(CN)2]2DNP}·4H2O system.

Theoretical insights into the effect of amine and phosphine decoration on the photoluminescence of copper(i) and silver(i) coordination polymers.

Coinage metal cyanides (MCN) form photoluminescent 1D coordination polymers. The decoration of these chains with amine and phosphine ligands shifts the wavelength for photoluminescence into the visible region. Density-functional theory (DFT) and time-dependent DFT (TD-DFT) calculations of zigzag and helical models of decorated chains are used to show that the transitions that contribute to the experimental spectra are related to the π-π excitations previously shown for coinage metal cyanide chains.

Structure and isomerization comparison of Zn(II), Cd(II) and Hg(II) perchlorate complexes of 2,6-bis([(2-pyridyl-methyl)amino]methyl)pyridine.

The divalent zinc triad perchlorate coordination chemistry of 2,6-bis([(2-pyridyl-methyl)amino]methyl)pyridine (L) was investigated by X-ray crystallography and solution state (1)H NMR. New complexes [HgL(ClO4)2] (1) and [CdL(ClO4)2] (2) were isolated as bicapped distorted square pyramidal racemates, contrasting with the approximate trigonal bipyramidal structure of [ZnL](ClO4)2 (3). Although rapid inter- and intramolecular exchange is common for simple complexes of zinc triad metal ions, conditions for slow intramolecular isomerization on both the δ and J(HH) time scales were established for 1, 2 and 3. Trends in geminal (1)H coupling suggested that an asymmetric structure was favored for all three metal ions at or below 40 °C. Contributions of a symmetric structure to solution equilibria were both temperature- and metal ion-dependent. Spectral trends were consistent with interconversion of a pair of enantiomeric square pyramidal ligand conformers through a symmetric trigonal bipyramidal ligand conformer by M-N bond cleavage and nitrogen inversion. Racemization was slower than the coupling constant time scale up to 40 °C for all complexes. Differential stabilization of specific small ligand conformations in solution has potential toxicological significance.

Multifunctionality of organometallic quinonoid metal complexes: surface chemistry, coordination polymers, and catalysts.

Quinonoid metal complexes have potential applications in surface chemistry, coordination polymers, and catalysts. Although quinonoid manganese tricarbonyl complexes have been used as secondary building units (SBUs) in the formation of novel metal-organometallic coordination networks and polymers, the potentially wider applications of these versatile linkers have not yet been recognized. In this Account, we focus on these diverse new applications of quinonoid metal complexes, and report on the variety of quinonoid metal complexes that we have synthesized. Through the use of [(η(6)-hydroquinone)Mn(CO)3](+), we are able to modify the surface of Fe3O4 and FePt nanoparticles (NPs). This process occurs either by the replacement of oleylamine with neutral [(η(5)-semiquinone)Mn(CO)3] at the NP surface, or by the binding of anionic [(η(4)-quinone)Mn(CO)3](-) upon further deprotonation of [(η(5)-semiquinone)Mn(CO)3] at the NP surface. We have demonstrated chemistry at the intersection of surface-modified NPs and coordination polymers through the growth of organometallic coordination polymers onto the surface modified Fe3O4 NPs. The resulting magnetic NP/organometallic coordination polymer hybrid material exhibited both the unique superparamagnetic behavior associated with Fe3O4 NPs and the paramagnetism attributable to the metal nodes, depending upon the magnetic range examined. By the use of functionalized [(η(5)-semiquinone)Mn(CO)3] complexes, we attained the formation of an organometallic monolayer on the surface of highly ordered pyrolitic graphite (HOPG). The resulting organometallic monolayer was not simply a random array of manganese atoms on the surface, but rather consisted of an alternating "up and down" spatial arrangement of Mn atoms extending from the HOPG surface due to hydrogen bonding of the quinonoid complexes. We also showed that the topology of metal atoms on the surface could be controlled through the use of quinonoid metal complexes. A quinonoid rhodium complex showed catalytic activity in Suzuki-Miyaura type reaction. As a result of the excellent stability of the homogeneous catalyst [(quinone)Rh(COD)](-) in water, we also successfully demonstrated catalyst recycling in 1,2- and 1,4-addition reactions. The compound [(quinone)Ir(COD)](-) showed significantly poorer catalytic activity in 1,4-addition reactions. Following upon the excellent coordination ability of the quinonoid rhodium complexes to metal centers, we synthesized organometallic coordination polymer nanocatalysts and silica gel-supported quinonoid rhodium catalysts, the latter using a surface sol-gel technique. The resulting heterogeneous catalysts showed activity in the stereospecific polymerization of phenylacetylene.