Redox-Controlled Self-Assembly of Vanadium-Seamed Hexameric Pyrogallol[4]Arene Nanocapsules.

Here we report the controlled self-assembly of vanadium-seamed metal-organic nanocapsules with specific metal oxidation state distributions. Three supramolecular assemblies composed of the same numbers of components including 24 metal centers and six pyrogallol[4]arene ligands were constructed: a VIII24L6 capsule, a mixed-valence VIII18VIV6L6 capsule, and a VIV24L6 capsule. Crystallographic studies of the new capsules reveal their remarkable structural complexity and geometries, while marked differences in metal oxidation state distribution greatly affect the photoelectric conversion properties of these assemblies. This work therefore represents a significant step forward in the construction of intricate metal-organic architectures with tailored structure and functionality.

A copper-seamed coordination nanocapsule as a semiconductor photocatalyst for molecular oxygen activation.

Here we report that a Cu2+-seamed coordination nanocapsule can serve as an efficient semiconductor photocatalyst for molecular oxygen activation. This capsule was constructed through a redox reaction facilitated self-assembly of cuprous bromide and C-pentyl-pyrogallol[4]arene. Photophysical and electrochemical studies revealed its strong visible-light absorption and photocurrent polarity switching effect. This novel molecular solid material is capable of activating molecular oxygen into reactive oxygen species under simulated sunlight irradiation. The oxygen activation process has been exploited for catalyzing aerobic oxidation reactions. The present work provides new insights into designing nonporous discrete metal-organic supramolecular assemblies for solar-driven molecular oxygen activation.

Synthesis, Characterization, and Stability of Dealkylated Salen-Supported Aluminum Phosphates.

Three salen aluminum bromide compounds salen(tBu)AlBr (1) (salen = N,N'-ethylenebis(3,5-di-tert-butylsalicylideneimine)), salpen(tBu)AlBr (2) (salpen = N,N'-propylenebis(3,5-di-tert-butylsalicylideneimine)), and salophen(tBu)AlBr (3) (salophen = N,N'-o-phenylenenebis(3,5-di-tert-butylsalicylideneimine) were evaluated for their potential use as dealkylation agents with a series of organophosphates. These reactions led to the aluminum phosphate compounds containing six-coordinate aluminum centers and hydrolytically stable P-O-C bonds: 4 = [salen(tBu)AlOP(O)(OMe)2]n, 5 = [salen(tBu)AlOP(O)(OEt)2]n, 6 = [salen(tBu)AlOP(O)(OPh)2]n, 7 = [salophen(tBu)AlOP(O)(OMe)2]n, 8 = [salpen(tBu)AlOP(O)(OiPr)2]2, 9 = (salen(tBu)AlO)3PO, 10 = (salpen(tBu)AlO)3PO, 11 = (salophen(tBu)AlO)3PO. All the compounds were characterized by 1H, 13C, 27Al, and 31P NMR, IR, and mass spectrometry. Furthermore, compounds 4-8 were structurally characterized by single-crystal X-ray diffraction. The potential hydrolysis of these compounds was modeled with 4 and demonstrated the unique stability of the final product and ease of isolation.

Self-Assembly of a Semiconductive and Photoactive Heterobimetallic Metal-Organic Capsule.

We report the synthesis of a novel metal-organic capsule constructed from six pyrogallol[4]arene macrocycles, which are switched together by 16 FeIII and 16 CoII ions. This supramolecular structure is the first instance of a spheroidal heterometallic nanocage assembled through a one-step metal-ligand coordination approach. This new assembly also demonstrates an important proof of concept through the formation of multiple heterometallic metal-metal interactions within the capsule framework. Photophysical and electrochemical studies of self-assembled capsule films indicate their potential as semiconductors. These materials display unexpected photoelectric conversion properties, thus representing an emergent phenomenon in discrete metal-organic supramolecular assemblies.

Controlled hierarchical self-assembly of networked coordination nanocapsules via the use of molecular chaperones.

Supramolecular chaperones play an important role in directing the assembly of multiple protein subunits and redox-active metal ions into precise, complex and functional quaternary structures. Here we report that hydroxyl tailed C-alkylpyrogallol[4]arene ligands and redox-active MnII ions, with the assistance of proline chaperone molecules, can assemble into two-dimensional (2D) and/or three-dimensional (3D) networked nanocapsules. Dimensionality is controlled by coordination between the exterior of nanocapsule subunits, and endohedral functionalization within the 2D system is achieved via chaperone guest encapsulation. The tailoring of surface properties of nanocapsules via coordination chemistry is also shown as an effective method for the fine-tuning magnetic properties, and electrochemical and spectroscopic studies support that the nanocapsule is an effective homogeneous water-oxidation electrocatalyst, operating at pH 6.07 with an exceptionally low overpotential of 368 mV.

Biomimetic Self-Assembly of CoII-Seamed Hexameric Metal-Organic Nanocapsules.

A CoII18L6 hexameric metal-organic nanocapsule (MONC) has been prepared and characterized using biomimetic self-assembly as the synthetic methodology. Akin to the biological behavior of zinc-finger proteins' release, uptake, and electrophilic substitution of Zn2+ ions, the assembly of this novel MONC has been accomplished by employing three sequential processes: assembly of the framework, metal ion insertion, and metal exchange, resulting in the formation of the CoII18L6 hexameric MONC. In this work, inspired by the biological behavior of metalloproteins, rational control of multiple complex supramolecular self-assembly has been achieved.

Lewis acid-assisted detection of nerve agents in water.

The five-coordinate compound, Salen((t)Bu)Al(Ac), prepared in situ from Salen((t)Bu)AlBr and NH4Ac, forms Lewis acid-base adducts in aqueous solution with the G-type nerve agents, Sarin and Soman, and the VX hydrolysis product, ethylmethylphosphonate (EMPA). The resulting compounds, [Salen((t)Bu)Al(NA)](+)[Ac] (-) (with NA = Sarin, Soman, and EMPA) are sufficiently stable to be identified by ESI-MS. Molecular ion peaks were detected for every compound with little or no fragmentation. The distinctive MS signatures for the [Salen((t)Bu)Al(NA)](+) compounds provide a new technique for identifying nerve agents from aqueous solution. The energetics of the displacement of Ac(-) by the nerve agents to form [Salen((t)Bu)Al(NA)](+)[Ac](-) were determined computationally.

C6H4S2AsCl: description and interpretation of an incommensurately modulated molecular crystal structure.

Crystals of 2-chloro-benzo-1,3,2-dithiarsole have a strongly modulated structure that can be solved and refined with relative ease in a P(1), Z' = 17 approximate supercell but that is better described as incommensurate. Two conventional refinements (different superstructure approximations that differ in the placement of their crystallographic inversion centers) and a (3 + 1)-dimensional superspace refinement are all nearly equally successful, at least as measured by the usual agreement factors; the data integration, however, shows that the incommensurate description is preferable. The overall packing is determined by the stacking of the aromatic rings and probably by the segregation of As and Cl atoms to give short As...Cl contacts. A refinement of the average (Z' = 1) structure shows that there are two basic orientations of the C6S2 plane, but that those orientations must be correlated in several directions to avoid impossibly short intermolecular contacts. Along the modulation vector q the orientation of the C6S2 plane varies smoothly, but q is not a direction in which the molecules are in contact. Along the directions in which the molecules are in contact the orientation of the C6S2 plane alternates; there are also positional shifts. The single modulation q relieves packing problems in several different directions well enough that crystals that diffract well can be grown.

Low-level mercury removal from groundwater using a synthetic chelating ligand.

Mercury is present in many industrial processes at low concentrations and is a cause for concern due to the propensity for mercury to bioaccumulate. As a cumulative toxin, introduction of mercury into the environment at any level has the potential to adversely affect ecologic systems. To date, no commercial precipitants are available that can irreversibly and permanently bind mercury. In the current work, selected commercial reagents were compared alongside the dianionic ligand 1,3-benzenediamidoethanethiolate (BDET(2-)) to test the feasibility of low-level (parts-per-billion, ppb) mercury treatment for groundwater near a chloralkali plant. Of all the reagents examined, only K(2)BDET was capable of reducing mercury concentrations to below instrumental detection limits of 0.05 ppb with the added benefit of producing a stable precipitate.

Mononuclear Schiff base boron halides: synthesis, characterization, and dealkylation of trimethyl phosphate.

A series of mononuclear boron halides of the type LBX(2) [LH = N-phenyl-3,5-di-tert-butylsalicylaldimine, X = Cl (2), Br (3)] and LBX [LH2 = N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (7), Br (8); LH2 = N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (9), Br (10); and LH2 = N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine, X = Cl (11), Br (12)] were synthesized from their borate precursors LB(OMe)2 (1) (LH = N-phenyl-3,5-di-tert-butylsalicylaldimine) and LB(OMe) [LH2 = N-(2-hydroxyphenyl)-3,5-di-tert-butylsalicylaldimine (4), N-(2-hydroxyethyl)-3,5-di-tert-butylsalicylaldimine (5), N-(3-hydroxypropyl)-3,5-di-tert-butylsalicylaldimine (6)]. The boron halide compounds were air and moisture sensitive, and upon hydrolysis, compound 7 resulted in the oxo-bridged compound 13 that contained two seven-membered boron heterocycles. The boron halide compounds dealkylated trimethyl phosphate in stoichiometric reactions to produce methyl halide and unidentified phosphate materials. Compounds 8 and 12 were found to be the most effective dealkylating agents. On reaction with tert-butyl diphenyl phosphinate, compound 8 produced a unique boron phosphinate compound LB(O)OPPh2 (14) containing a terminal phosphinate group. Compounds 1-14 were characterized by 1H, 13C, 11B, 31P NMR, IR, MS, EA, and MP. Compounds 5, 6, and 11-14 also were characterized by single-crystal X-ray diffraction.

Mercury(II) 2-aminoethanethiolate clusters: intramolecular transformations and mechanisms.

The combination of HgF2 and 2-aminoethanethiol (AET, with some AET.HCl present) yielded a cyclic tetranuclear thiolate, [Hg4Cl4(SCH2CH2NH2)4] (1), with alternating Hg and S atoms. The Cl from the reaction mixture led to the formation of Hg-Cl bonds with no Hg-F in the final product. In contrast, a similar reaction with HgBr2 yielded a nonanuclear cluster, [Hg9Br15(SCH2CH2NH3)15]3+ (2), and the disulfide salt {[HgBr4][(NH3CH2CH2S-)2]} (3). Despite similar reactions, the AET groups in 2 are protonated compared to the nonprotonated amine groups in 1, which allows the ligand to chelate the Hg atom in the latter compound. The reaction with HgI2 yielded a cyclic tetranuclear compound, [Hg4I6(SCH2CH2NH2)2(SCH2CH2NH3)2](H2O/EtOH) (4), containing protonated and nonprotonated AET groups. Compound 4 at room temperature irreversibly rearranges to [Hg4I4(SCH2CH2NH2)4] (5), which is isostructural to 1. A systematic pathway for the formation of 1 along with the intramolecular conversion of 4 to 5 is proposed. These compounds demonstrate that very diverse Hg-S compounds form under similar reaction conditions.

Aluminum phosphinate and phosphates of salen ligands.

A new dealkylation reaction between organophosphate esters and Salen aluminum bromide compounds has been used to prepare three new aluminum salen compounds salen((t)Bu)AlOP(O)Ph2 (1) (salen = N,N'-ethylenebis(3,5-di-tert-butylsalicylideneimine)), [(MeOH)Alsalen((t)Bu)[OMePO2(O)]Alsalen((t)Bu)[OMePO2(O)]Alsalen((t)Bu)]Br (2), and [salpen((t)Bu)AlO]2[(BuO)2PO]2 (3) (salpen = N,N'-propylenebis(3,5-di-tert-butylsalicylideneimine)). Compounds 1.MeOH, 2, and 3 were characterized by single-crystal X-ray diffraction. Compound 1 is the first example of a monomeric aluminum Schiff base phosphinate. Compound 2 is a cationic Salen aluminum phosphate, and compound 3 contains an aluminophosphate ring. This work is the first example of the intentional use of an aluminum-based dealkylation reaction to form new compounds.

Solution and solid-state study of heteroleptic Hg(II)-thiolates: crystal structures of [Hg4I4(SCH2CH2NH2)4] and [Hg4I8(SCH2CH2NH3)2]n.nH2O.

Combination of 2-aminoethanethiol hydrochloride and HgI2 in water in the presence of a base yielded a cyclic molecular structure, [Hg4I4(SCH2CH2NH2)4] (1). For the same reaction in the absence of the base, a similar structure with protonated amines was expected; however, polymeric [Hg4I8(SCH2CH2NH3)2]n.nH2O2 was formed instead. The structures are quite variable despite similar reaction conditions. For instance, there is an additional Hg-N interaction in 1 due to the use of base. The environment around tetracoordinate Hg in 1 is comprised of S, N, and I atoms, with the ligand forming a five-membered chelate and the I atoms present alternate to each other. In the repeating unit of 2, three independent types of Hg atoms are observed, with HgSI3, HgS2I2, and HgI4 bonding environments that have both bridging and terminal I atoms. A simple mechanistic pathway for the formation of 1 and 2 is proposed that includes the presence of three- and four-coordinate Hg intermediates in the solution. Intermolecular hydrogen bonding involving N, I, and S in 1 and N, I, and O atoms in 2 create extended three-dimensional networks. The shortest Hg... Hg distances are found to be intrachain in the range 3.938-3.962 A and indicate no interaction between these atoms. The solution studies (UV-vis and NMR) along with solid-state (IR, Raman, and X-ray) studies for 1 and 2 confirm retention of the structural configuration in the solution. The thermal study of 2 indicates that degradation of the complex occurs in a single step, in contrast to 1, which takes a more complicated decomposition pathway.

Five-coordinate aluminum bromides: synthesis, structure, cation formation, and cleavage of phosphate ester bonds.

The alkane elimination reaction between Salen((t)Bu)H(2) ligands and diethylaluminum bromide was used to prepare three Salen aluminum bromide compounds salen((t)Bu)AlBr (1) (salen = N,N'-ethylenebis(3,5-di-tert-butylsalicylideneimine)), salpen((t)Bu)AlBr (2) (salpen = N,N'-propylenebis(3,5-di-tert-butylsalicylideneimine)), and salophen((t)Bu)AlBr (3) (salophen = N,N'-o-phenylenenebis(3,5-di-tert-butylsalicylideneimine)). The compounds contain five-coordinate aluminum either in a distorted square pyramidal or a trigonal bipyramidal environment. The bromide group in these compounds could be displaced by triphenylphosphine oxide or triphenyl phosphate to produce the six-coordinate cationic aluminum compounds [salen((t)Bu)Al(Ph(3)PO)(2)]Br (4), [salpen((t)Bu)Al(Ph(3)PO)(2)]Br (5), [salophen((t)Bu)Al(Ph(3)PO)(2)]Br (6), and [salophen((t)Bu)Al[(PhO)(3)PO)](2)]Br (7). All the compounds were characterized by (1)H, (13)C, (27)Al, and (31)P NMR, IR, mass spectrometry, and melting point. Furthermore, compounds 1-3 and 5-7 were structurally characterized by single-crystal X-ray diffraction. Compounds 1-3 dealkylated a series of organophosphates in stoichiometric reactions by breaking the ester C-O bond. Also, they were catalytic in the dealkylation reaction between trimethyl phosphate and added boron tribromide.

Mercurophilic interaction in novel polynuclear Hg(II)-2-aminoethanethiolates.

The reaction of 2-aminoethanethiol hydrochloride with Hg(2)Cl(2) in water yielded elemental mercury and one-dimensional polynuclear compounds [{Hg(3)Cl(5)(SCH(2)CH(2)NH(3))(3)}Cl](n) and [HgCl(SCH(2)CH(2)NH(2))(H(2)O)(2)](n) (2). The coordination environment around Hg in 1 and 2 is quite variable despite similar reaction conditions. The formation of a five-membered S/N chelate in 2 can be attributed to the use of base to produce a neutral ligand. Three independent types of Hg atoms, both three- and four-coordinate are observed in 1, whereas in 2, the Hg atom is tetracoordinate with S, N and Cl atoms in the primary coordination sphere. Despite distinct structural chemistry, the coordination environments in 1 and 2 are fairly similar with repeating units connected with bridged thiolate S atoms in addition to a terminal Cl attached to Hg. Intermolecular hydrogen-bonding involving amine protons, Cl and water molecules are responsible for a three-dimensional network in both 1 and 2. A short Hg...Hg distance of 3.564 A, indicates the presence of a mercurophilic interaction in 1. The compounds have been characterized by (1)H and (13)C NMR, UV-Vis, FT-IR, Raman, mass spectrometry, TGA and single X-ray crystallography.

Structure-directing influence of halide in mercury thiolate clusters.

Under identical conditions, the reaction of 2-aminoethanethiol hydrochloride with HgX(2) (X = Cl and Br) in water yielded discrete hexanuclear [Hg(6)Cl(8)(SCH(2)CH(2)NH(3))(8))]Cl(4).4H(2)O (1) and nonanuclear [Hg(9)Br(15)(SCH(2)CH(2)NH(3))(9)](Cl(0.8)Br(0.2))(3) (2) complexes with unusual coordination environments. Compound 1 crystallizes as triclinic with a = 9.434(2) Angstroms, b = 10.999(2) Angstroms, c = 13.675(7) Angstroms, alpha = 92.9(7) degrees, beta = 105.2(7) degrees, and gamma = 96.9(7) degrees, whereas 2 is monoclinic with a = 14.162(3) Angstroms, b = 8.009(16) Angstroms, c = 19.604(4) Angstroms, alpha = gamma = 90.0 degrees, and beta = 92.7(3) degrees. In both cases, it is observed that the halide creates the secondary structure around trinuclear units (dimer in 1 and trimer in 2) through Hg-X bonding. Two independent types of Hg atoms (four- and five-coordinate in 1) and (three- and four-coordinate in 2) are observed. The geometry around Hg is quite variable with bridging thiolate and both bridging and terminal halides. The angles around Hg associated with the S atoms are more obtuse than expected from mercury(II) thiolates with a coordination number of more than 2. Intermolecular hydrogen bonding involving NH(3)(+), water molecules, and the halide atoms is responsible for the three-dimensional network in both compounds. Relatively short Hg...Hg interactions in 1 (3.797 and 3.776 Angstroms) and in 2 (3.605 and 3.750 Angstroms) are also observed. The compounds have been characterized with the help of (1)H and (13)C NMR, UV-Vis, infrared, Raman, and mass spectrometry, thermogravimetric analysis, and single X-ray crystallography.

Soft metal preferences of 1,3-benzenediamidoethanethiol.

Recent studies indicate that the sodium salt of 1,3-benzenediamidoethanethiol (BDET) is both economical and effective in precipitating mercury and other heavy metals from water. Because wastewaters and contaminated natural waters may contain a variety of heavy metals, it is important to determine how different heavy metals may interact with BDET, and whether free metals may displace those that are bound. To explore this possibility, Cd-, Cu-, Pb-, Mn-, Hg- and Zn-BDET were leached separately under a nitrogen purge for up to 240 h in pH 3 aqueous solutions containing 0.100 mmol of all five heavy metals. The leaching studies indicate that dissolved Hg has a strong tendency to displace Cd, Cu, Mn, Pb, and Zn from the BDET structure.