On the resonance energy in new all-metal aromatic molecules

We have recently advanced the aromaticity concept into all-metal molecules containing Al(4)(2-), XAl(3)(-), Ga(4)(2-), In(4)(2-), Hg(4)(6-), Al(3)(-), and Ga(3)(-) aromatic units. All these systems are electron deficient species compared to the corresponding aromatic hydrocarbons. The electron deficiency results in an interesting new feature in all-metal aromatic systems, which should be considered as having both pi- and sigma-aromaticity, and that should result in their additional stability. In this work, we obtain crude evaluations of the resonance energies for Na(2)Al(4) and Na(2)Ga(4) all-metal aromatic molecules. The resonance energies were found to be unusually high: 30 kcal/mol (B3LYP/6-311+G*) and 48 kcal/mol (CCSD(T)/6-311+G(2df)) for Na(2)Al(4) and 21 kcal/mol (B3LYP/6-311+G*) for Na(2)Ga(4) compared to 20 kcal/mol in benzene. We believe that the high resonance energies in Na(2)Al(4) and in Na(2)Ga(4) are due to the presence of three completely delocalized bonds, one pi-bond and two sigma-bonds, thus confirming the presence of pi- and sigma-aromaticity.     

An unexpected silver triflate catalyzed reaction of 2-alkynylbenzaldehyde with 2-isocyanoacetate

An unexpected silver triflate catalyzed reaction of 2-alkynylbenzaldehyde with 2-isocyanoacetate provides an efficient route for the generation of isoquinolines. The reaction proceeds smoothly in air under mild conditions with high efficiency.     

Anion exchange induced tunable catalysis properties of an uncommon butterfly-like tetranuclear copper(II) cluster and magnetic characterization

An uncommon butterfly-like tetranuclear copper(ii) cluster with the formula {[Cu(4)(μ(3)-OH)(2)(μ(4)-Cl)(H(2)O)(2)(L)(2)]·Cl(H(2)O)(7)}(n) (1) (H(2)L = 1,2-bis[3-(1,2,4-triazolyl)-4-amino-5-carboxylmethylthio]ethane) has been synthesized. Compound 1 exhibits interesting anion exchange characteristics, in which both guest and coordinated Cl(-) can be replaced by I(-) or NO(3)(-) in water. Furthermore, a high catalytic selectivity to produce poly(phenylene ether) by the oxidative coupling of 2,6-dimethylphenol in water is found to be 74% for 1 and 87% for the anion-exchanged product 1-MI(x), respectively. Additionally, the antiferromagnetic interaction among Cu ions for compound 1 is also found.     

Structure and magnetism of a porous three-dimensional metal-organic framework based on planar tetranuclear copper(II) cluster units

A porous three-dimensional copper(II) metal-organic framework (MOF) {[Cu₂(tci)(OH)(pip)_0.5(H₂O)]·6H₂O} _n (1) [tci = tris (2-carboxyethyl)isocyanurate, pip = piperazine] has been generated under hydrothermal conditions at 120 °C. Single crystal X-ray diffraction reveals that the polymer exhibits a novel three-dimensional framework based on planar tetranuclear copper(II) cluster units. The variable temperature magnetic susceptibility data in the range 2–280 K show antiferromagnetic spin-spin coupling in the tetranuclear unit in complex 1. A theoretical fitting of the magnetic data gives J values of ?31.3 cm^?1, ?30.8 cm^?1, and 13.5 cm^?1.     

A C-terminal domain of the membrane copper pump Ctr1 exchanges copper(I) with the copper chaperone Atx1

A cloned C-terminal domain of the yeast high-affinity copper uptake pump Ctr1 exchanges Cu(I) rapidly with the yeast copper chaperone Atx1: 10(-2) < Kex < 10(+2).     

An organometallic tetranuclear cluster with phosphine and phosphido ligands in nonclassical bonding modes: X-ray structural characterization

The elimination of the NCMe ligand in [(C₆F₅)₂Pt(μ-PPh₂)₂M(NCCH₃)₂] (M = Pd, Pt) results in the formation of the tetranuclear clusters [Pt₂Pd₂(μ-PPh₂)₃(C₆F₅)₃(PPh₂C₆F₅)] 1 and [Pt₄(μ-PPh₂)₄(C₆F₅)₄] 2. The structure of 1 indicates that one of the palladium centres is connected to the rest of the centres through two M-M bonds and two weaker η²-C₆H₅ and η²-P-C interactions.     

Interplay among aromaticity, magnetism, and nonlinear optical response in all-metal aromatic systems

All-metal aromatic molecules are the latest inclusion in the family of aromatic systems. Two different classes of all-metal aromatic clusters are primarily identified: one is aromatic only in the low spin state, and the other shows aromaticity even in high-spin situations. This observation prompts us to investigate the effect of spin multiplicity on aromaticity, taking Al(4)(2-), Te(2)As(2)(2-), and their copper complexes as reference systems. Among these clusters, it has been found that the molecules that are aromatic only in their singlet state manifest antiaromaticity in their triplet state. The aromaticity in the singlet state is characterized by the diatropic ring current circulated through the bonds, which are cleaved to generate excess spin density on the atoms in the antiaromatic triplet state. Hence, in such systems, an antagonistic relationship between aromaticity and high-spin situations emerges. On the other hand, in the case of triplet aromatic molecules, the magnetic orbitals and the orbitals maintaining aromaticity are different; hence, aromaticity is not depleted in the high-spin state. The nonlinear optical (NLO) behavior of the same set of clusters in different spin states has also been addressed. We correlate the second hyperpolarizability and spin density in order to judge the effect of spin multiplicity on third-order NLO response. This correlation reveals a high degree of NLO behavior in systems with excess spin density. The variance of aromaticity and NLO response with spin multiplicity is found to stem from a single aspect, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and eventually the interplay among aromaticity, magnetism, and NLO response in such materials is established. Hence, the HOMO-LUMO energy gap becomes the cornerstone for tuning the interplay. This correlation among the said properties is not system-specific and thus can be envisaged even beyond the periphery of all-metal aromatic clusters. Such interplay is of crucial importance in tailoring novel paradigm of multifunctional materials.     

Structure and dynamics of Cu(I) binding in copper chaperones Atox1 and CopZ: a computer simulation study

Copper chaperones deliver reduced copper (i.e., Cu(I)) to metal-binding domains of P-type ATPases in the cytoplasm of a range of organisms. Both chaperones and target domains have a ferredoxin-like fold and metal-binding motifs involving two Cys residues. Here, we investigated the Cu-binding geometry and structural dynamics of two homologous Cu(I) chaperones, Homo sapiens Atox1 and Bacillus subtilis CopZ, using a combination of quantum mechanical-molecular mechanics (QM-MM) and classical molecular dynamics (MD) methods. Our QM-MM optimized geometries for the holo- proteins suggested that Cu(I) in Atox1 favors a linear Cys(S)-Cu-Cys(S) arrangement but that this angle is close to 150 degrees in CopZ. Classical MD simulations suggest that both Atox1 and CopZ apo- forms have an increased conformational flexibility as compared to the respective holo- forms. This difference is most pronounced in CopZ and correlates with a lower in vitro thermal stability. Both average fluctuation (i.e., rmsd) and radius of gyration data demonstrate that the effects of Cu(I) coordination extend throughout the proteins. Distinct deviations between the two homologues were found in protein-solvent interactions, entropy of Cu(I) binding, and apo-protein Cys-Cys distance distributions. Our in silico results provide new insights into copper chaperone behavior with direct implications for copper transport mechanisms in vivo.     

Aromaticity and electronic delocalization in all-metal clusters with single, double, and triple aromatic character

A series of monocyclic planar inorganic compounds with single, double, and triple (anti)aromatic character has been studied. The electron delocalization and aromaticity of these compounds have been assessed by means of two-center and multicenter electronic delocalization indices and their ??-, ??-, and ??-components. Results show that these indices are excellent predictors of the ??-, ??-, and ??-aromatic character of all-metal and semimetal clusters.     

Two unprecedented 1D coordination polymer chains based on tetranuclear copper(II) building blocks

The reaction of copper(II) sulfate with pyridine in DMF or methanol yield two unprecedented Cu(II) coordination polymers {[Cu₄(μ₄-O)(py)₄(SO₄)₄][μ-Cu(py)(DMF)₂]}_n(1) and {[Cu₄(μ₄-O)(py)₄(SO₄)₄][μ-Cu(py)₄]}_n(2), respectively. Single-crystal X-ray diffraction indicated that compound 1 crystallizes in the monoclinic system, space group p2(1)/n, a=14.542(5) Å, b=16.359(5) Å, c=18.951(5) Å, β=92.047(5)°, V=4505(2) Å³, Z=4 while 2 is monoclinic C2/c, a=23.078(5) Å, b=10.214(5) Å, c=23.142(5) Å, β=115.471(5)°, V=4925(3) Å³, Z=4. Both of the two compounds consist of tetrahedral tetranuclear [Cu₄(μ₄-O)(py)₄(SO₄)₄] clusters that are bridged by pentacoordinated Cu atom for 1 or hexacoordinated Cu atoms for 2 through the sulfate oxygen to form the infinite one-dimensional polymer chains.     

An unexpected silver triflate-catalyzed tandem reaction of N'-(2-alkynylbenzylidene)hydrazide with ketene

An unexpected silver triflate-catalyzed tandem reaction of N'-(2-alkynylbenzylidene)hydrazide with ketene through 6-endo-cyclization, [3+2] cycloaddition and rearrangement is reported. This reaction proceeds efficiently to generate the molecular complexity with the formation of four bonds in a one-pot procedure.     

Temperature-dependent crystal structure and fluorescence properties of a tetranuclear copper(I) cluster from in situ [2 + 3] cycloaddition synthesis

Hydrothermal reaction of CuSO₄·7H₂O and NaN₃ with 2-cyanothiophene in aqueous ethanol yielded a novel tetranuclear copper(I) polymer, {[Cu₄(tptz)₄]·0.5(C₂H₆O)}_n (1) (Htptz = 5-(thiophen-2-yl)-1H-tetrazole). The tptz ligand in the complex was generated through an in situ [2 + 3] cycloaddition reaction involving the cyano groups of the precursor 2-cyanothiophene. In a rare example, three different geometries of Cu(I) cations, namely the linear, triangle, and tetrahedron geometries of Cu(I) centers, are created and linked by Htptz ligands into a 1-D ladder structure. Additionally, 1 exhibits strong blue fluorescence (with λ = 467 nm) at room temperature in the solid state.