Theoretical evidence of d‐orbital aromaticity in anionic metal X (X = Sc,Y, La) clusters

The equilibrium geometries, total electronic energies, and vibrational frequencies for singlet, triplet, and quinted states of three all‐metal X (X = Sc, Y, and La) anions and nine relevant neutral singlet MX₃ (M = Li, Na, K, X = Sc, Y, La) clusters are investigated with four density functional theory (DFT) and correlated ab initio methods B3LYP, B3PW91, MP2, and CCSD(T). To our knowledge, the theoretical study on these clusters composed of the transition metal Sc, Y, La is first reported here. The calculated results show that for the X clusters the singlet states with trigonal D_3h structures are the lowest energetically, while the neutral singlet MX₃ clusters each have two stable isomers: one trigonal pyramidal C_3v and one bidentate C_2v structures with the pyramidal C_3v isomer being ground state. In addition, we calculate the resonance energies (RE) and nucleus‐independent chemical shift (NICS) for the singlet trigonal X rings and show that these singlet trigonal X rings exhibit higher degree of aromaticity. The detailed molecular orbital (MO) analyses reveal that the singlet trigonal X anions have one delocalized σ‐type and one delocalized π‐type MOs, which follow the 4n + 2 electron counting rule, respectively and play an important role in rendering these species two‐fold aromaticity. Here, an explicit theoretical evidence is given to prove that the contribution to the two‐fold aromaticity of the singlet trigonal X (X = Sc, Y, and La) rings originates primarily from the d‐orbital bonding interactions of these component transition metal X atoms. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Spectral,Thermal and Structural Studies of Two 3D Coordination Polymers Based on Tetracarboxylic Ligand

Two new coordination polymers,[M_6L_3(DMA)_3(H_2O)](M=Zn for 1,Cu for 2,L=tetrakis[3-(carboxyphenyl)oxamethyl]methane acid,DMA = N,N-dimethylacetamide) have been solvothermally synthesized. Single-crystal X-ray diffraction analysis reveals that compounds 1 and 2 are isostructural and crystallize in the trigonal space group R. The asymmetrical unit contains two metal ions,one L~(4-) ligand and two coordinated DMA molecules. The metal ions are connected through six aromatic rings into a linear trimetallic zinc building unit. The whole structure is connected through tetrehedral ligand and the trimetallic building units to form a 4,6-connected framework of the toc topology. Compounds 1 and 2 are further studied by IR spectroscopy,thermogravimetric analyses and PXRD. The solid-state UV-Vis and photoluminescent properties of compounds 1 are also investigated.     

新的富金属三组元层状碲化物TaNi2Te2的合成和晶体结构

通过高温固相反应合成了标题化合物并测定了其晶体结构．结晶学参数：正交晶系，空间群Pnma，Z＝4，α＝0.6480(1)；b＝0.35639(6)，c＝1.6994(4) nm，V＝0.3925(1) nm，D_c＝9.37 g·cm~(-3)，λ(MoK_α)＝0.071069 nm，μ(MoK_α)＝514.43 cm~(－1)，F(000)＝932，最终偏离因子R＝0.051．TaNi_2Te_2是一新的富金属三级元层状碲化物，在结构中两层金属原子夹于碲原子层之间，形成对Ta原子的平面三角形碲配位和对Ni原子的三角锥碲配位．演化合物的一个重要结构特征是平面形的五元环TeNi_4孪合形成扩展结构而每个Ta原子夹于两个TeNi_4五元环之间．     

povel isomers of hexasulfur: Prediction of a stable prism isomer and implications for the thermal reactivity of elemental sulfur

High-level ab initio molecular orbital calculations were employed to explore the potential energy hypersurface of hexasulfur, S(6). Twelve isomeric structures of S(6) have been identified: two unbranched rings (chair and boat), one trigonal prism of D(3h) symmetry, two singly branched rings (S(5)double bondS), three triplet chains, one singlet chain, and three doubly branched rings (Sdouble bondS(4)double bondS). The prism structure is essentially a cluster of three S(2) molecules connected via a six-center pi(*)-pi(*)-pi(*) interaction. It is by 51 kJ mol(-1) less stable than the lowest-energy chair form. The reactions to generate the boat, the prism, and the singly branched isomers from the chair form are predicted to have lower barriers than the ring opening reaction of cyclo-S(6), which requires an activation energy of 149 kJ mol(-1). The prism and singly branched isomers are found to be more reactive species than the chair form and they are potential sources of S(2) in chemical reactions involving elemental sulfur.     

Preparation and Structure of A Novel Ethanolamine-occluding Aluminoarsenate

An aluminoarsenate, Al2As2O3.EAN, denoted as AlAsO4-1 was synthesized from EAN(EAN= ethanolamine), pyroarsenic acid and aluminium-iso-propylate systems. The crystal structure of AlAsO4-1 was determined by single crystal X-ray diffraction method. The compound crystallizes in orthorhombic space group Pcab with the unit cell constants:0 = 8.781(3), 6=10.261(3), c=20. 433(11) A .V = 1840.9 A3, 2=8. The final R and Rw factors are 0. 0401 and 0. 0344, respectively. The framework of AlAsO4-1 contains two types of Al atoms. It is interesting that in the asymmetric unit one of two Al atoms is strictly 4-coordinated and the other is 6-coordinated. The three-dimensional framework is built of two-dimensional nets which consist of 4-membered rings and 8-membered rings. The biggest open channel in the framework runs along [100], in which EAN template is located. Arsenic atoms can function as a component element for construction of three-dimensional net with topological novelty.     

Racemization of R-Naproxen Ester Using Microwave Oven

(S)-(+)-2-(6-methoxy-2-naphthyl) propionic acid (Naproxen) is a nonsteroidal antiinflammatory drug which belongs to the family of 2-aryl propionic acid derivatives, which is widely used as a drug for human connective tissue diseases. The physiological activity of the S-form Naproxen is 28-fold that of the R-form^[1]. Hence, only the S-form is used as a drug for human diseases.     

三环己基锡邻(二茂铁甲酰基)苯甲酸酯配位聚合物的微波固相合成、晶体结构及性能

在微波辐射下, 邻二茂铁甲酰基苯甲酸与三环己基氢氧化锡反应, 合成了结构新颖的含铁锡多核配合物. 紫外光谱、 红外光谱、 核磁共振谱、 元素分析和X射线晶体衍射表征结果表明, 配合物的中心锡与配基原子形成五配位畸变三角双锥构型, 通过配体的羧基氧和羰基氧原子分别与锡原子连接形成一维链配位聚合物. 热分析结果表明, 配合物在163 ℃以下具有较好的热稳定性. 其溶液在电极上能准可逆电子转移, 对人体细胞HT-29, MCF-7, HepG2, KB和A549的体外抗癌活性均高于对照药顺铂, 具有潜在应用价值.     

Comparative semiempirical and ab initio study of the structural and chemical properties of uric acid and its anions

Semiempirical, density functional theory (DFT), and ab initio calculations have been performed to assess the relative stabilities of 15 possible tautomer forms of neutral uric acid, and of the different urate mono‐ and dianion forms. These methods have also been used to compute ionization potentials (IPs) for uric acid and its derived anions. Overall, we have found that semiempirical calculations, in particular PM3, perform well as compared with B3LYP or MP2 computations toward these different structural and chemical properties of uric acid: the triketo form of uric acid is the most stable tautomer form of neutral uric acid. Three other tautomer forms are relatively close in energy, within the range 2–6 kcal/mol above the triketo form, with a mean energy deviation of only 1.3 kcal/mol between PM3 and DFT or ab initio results; the monoanion form of uric acid obtained by abstracting one proton in position 3 (denoted UAN) is the most stable form among all four possible urate monoanions both in gas phase and in solution; the dianion form of uric acid obtained by abstracting two protons, respectively, in positions 3 and 9 of uric acid (denoted UANN) is the most stable urate dianion form both in gas phase and in solution. However, these two most stable species do not have the lowest IPs in solution: among monoanions and dianions, respectively, the species with the lowest IPs are UAN and UANN. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Electrochemical carboxylation of β-cyclodextrin/1-(3-phenoxyphenyl)-1-chloroethane inclusion complex on a glassy-carbon cathode in anhydrous dimethylformamide

Inclusion complexes of β-cyclodextrin with 1-(3-phenoxyphenyl)-1-chloroethane in the “guest-host” molar ratio of 1: 2 are synthesized, isolated, and characterized. It is shown that preparative electrocarboxylation of β-cyclodextrin/1-(3-phenoxyphenyl)-1-chloroethane inclusion complex on a glassy-carbon cathode in dimethylformamide leads to the formation of S-form of 2-(3-phenoxyphenyl)propionic acid (S-Phenoprofen) with an optical yield of ～20%. In addition to the acid, a dimer of electrochemically generated intermediates forms.     

Distribution of aluminum and boron in the periodical building units of boron-containing Beta zeolites

Various boron only ([B]-BEA) as well as aluminum- and boron-containing beta zeolites ([Al,B]-BEA) have been prepared and modified by ion exchange of ammonium, sodium, and nickel ions. The zeolite samples have been characterized by 11B, 27Al, and 29Si MAS as well as three of them by 11B and 27Al 3Q-MAS NMR spectroscopy. The quantitative contributions of defect-free Si(nX) (n = 2, 1, 0; X = Al, B) and Si(OH)x (x = 2, 1) sites to the NMR signal intensities were calculated from the various Si/(Al + B) ratios and relative 11B, 27Al, and 29Si NMR signal intensities using the special distribution of aluminum and boron in different periodical building units of the zeolite framework. The boron atoms are sitting exclusively in diagonal positions in the four-membered rings of [B]-BEA zeolites, while the aluminum atoms are situated both in diagonal and lone positions in the four-membered rings of [Al,B]-BEA zeolites. A higher part of boron atoms are positioned in framework-related deformed tetrahedral boron species than in lattice positions in the [B]-BEA than in the [Al,B]-BEA zeolites. All extraframework octahedral aluminum species are transformed back to lattice positions due to ion exchange from the protonated form to ammonium-, sodium-, or nickel-ions containing zeolites. Oppositely, trigonal boron leaves the zeolite structure completely during ion exchange.     

Cobalt and manganese diphosphonates with one-, two-, and three-dimensional structures and field-induced magnetic transitions

Reactions of 2-(1-Imidazole)-1-hydroxyl-1,1'-ethylidenediphosphonic acid (ImhedpH(4)) and cobalt or manganese salts under hydrothermal conditions result in three new metal diphosphonates: β-Co(3)(ImhedpH)(2)(H(2)O)(4)·2H(2)O (1), Co(3)(ImhedpH)(2)(H(2)O)(4) (2), and Mn(ImhedpH(2))·H(2)O (3). In compound 1, the columns made up of {Co1(2)O(2)} dimers and {PO(3)C} tetrahedra through corner-sharing are cross-linked through {Co2O(6)} octahedra, forming an inorganic layer. Neighboring layers are pillared by coordinated imidazole groups of ImhedpH(-) ligands, leading to a three-dimensional open framework containing two kinds of channels with sizes of 8.256 × 9.851 ? and 8.030 × 4.745 ? (van der Waals radii not accounted for). Compound 2 shows a layer structure, in which Co(3)(ImhedpH)(2)(H(2)O)(4) trimer units are connected through the corner-sharing of {Co1O(5)} trigonal bipyramids and {PO(3)C} tetrahedra, forming an inorganic layer containing 20-member rings composed of six Co atoms, two μ(3)-O1 units, and four O-P-O units. The noncoordinated imidazole groups protrude from two sides of the layer. Compound 3 shows a ladder structure, where the Mn(II) ions are bridged by ImhedpH(2)(2-) ligands through double O-P-O units to form a single chain, and two such chains are further fused together by sharing edges of {MnO(5)} trigonal bipyramids. The magnetic properties of 1-3 have been studied. Ferrimagnetism and field-induced magnetic transition from ferrimagnetism to a fully polarized state are observed in 1. Compounds 2 and 3 reveal dominant antiferromagnetic interactions between metal centers, and two-step field-induced magnetic phase transitions are found in 2.     

Synthesis, structures and catalytic properties of iron(III) complexes with asymmetric N-capped tripodal NO3 ligands and a pentadentate N2O3 ligand

A new family of N-capped tripodal NO(3) proligands N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N-(2'-hydroxy-5'-R-phenyl)amine [H(3)(L(n))] [when R= Me, n = 1; R= (t)Bu, n = 2; R = Cl, n = 3] with different substituents in one of the aryl rings and N,N-bis(2-hydroxy-3-tert-butylbenzyl)-N-(2'-hydroxy-5'-methylphenyl)amine [H(3)(L(4))] were synthesised. The preparation of a new pentadentate proligand N-methyl-N,N',N'-tris(2-hydroxy-3,5-di-tert-butylbenzyl)ethane-1,2-diamine [H(3)(L(5))] with an N(2)O(3) donor set is also reported. Reaction of the proligands [H(3)(L(n))] (n = 1-4) with iron(iii) chloride in the presence of base (triethylamine) and 1-methylimidazole (1-Meim) as co-ligand led to the formation of iron complexes of the type [Fe(L(n))(1-Meim)] (n = 1-4) () respectively, while treatment of the trilithium salt of [H(3)(L(5))] with iron(iii) chloride afforded [Fe(L(5))] (). All complexes were structurally characterised by X-ray crystallography. In complexes , the ligands form five- and six-membered chelate rings with the iron centres which have distorted trigonal bipyramidal geometry with an N(2)O(3) coordination environment. Complex adopts a similar distorted trigonal bipyramidal geometry also with N(2)O(3) coordination around the iron centre. The catalytic activity of these iron complexes towards epoxidation of styrene was examined.     

Synthesis of a Fluorescent Polymer Bearing Covalently Linked Thienylene Moieties and Rhodamine for Efficient Sensing

A novel conjugated polymer (RB‐PPETE) of poly[p‐(phenylene ethynylene)‐alt‐(thienylene ethynylene)] (PPETE) bearing covalently linked thienylene rings and Rhodamine B units has been synthesized and successfully used to detect metal ions. The Rhodamine B exists as a lactone, which is colorless and non‐fluorescent. Hg²⁺ ions can induce the Rhodamine group to form a ring‐opened state. The fluorescence resonance energy transfer (FRET) was demonstrated in the polymer, and in the presence of Hg²⁺ ions the excitation energy along the backbone of the conjugated polymer is transferred to the energy acceptor (Rhodamine B), which leads to a visual color change of the solution from slight yellow to orange. Meanwhile, this new system shows outstanding Hg²⁺‐selective FRET off–on type fluoroionophoric properties among the representative metal ions in tetrahydrofuran.

     

Theoretical study of aromaticity in small hydrogen and metal cation clusters X (X=H,Li, Na,K, and Cu)

Five cation clusters X (X=H, Li, Na, K, and Cu) with two possible isomers, i.e., regular trigonal structure (D_3h) and linear structure (D_∞h), have been investigated using four methods: B3LYP, B3PW91, MP2, CCSD(T) and basis set 6‐311+G(3df). The calculations show that only the regular trigonal structure (D_3h) is stable. The related neutral clusters X₃Cl (X=H, Li, Na, K, and Cu) are also investigated using two methods: B3LYP, MP2, and basis set 6‐311+G(3df). For H₃Cl species, there is no a stable structure to be found. For other four X₃Cl (X=Li, Na, K, and Cu) species, there are two stable isomers, for which the bidentate structures (C_2v‐1) [see Fig. 1 (d)] are global minima. According to the general criteria for aromaticity including resonance energy (RE) and nucleus‐independent chemical shift (NICS), the five trigonal isomers exhibit a higher degree of aromaticity. Molecular orbital analysis reveals that the five trigonal X(X=H, Li, Na, K, and Cu) isomers possess only σ‐aromaticity originating from s orbitals. For the Cu ring the d orbitals do not play a significant role in the electron delocalization effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Structurally characterized group 4 metal alkoxides modified with the pyridyl-based ligands 2-mercapto pyridine n-oxide and 3,3′-dihydroxy-2,2′-bipyridine

An investigation of a series of substituted pyridyl-based ligands was undertaken using 2-mercapto pyridine n-oxide (H-2MPO) and 3,3′-dihydroxy-2,2′-bipyridine (H₂-OBPy) as the modifying reagents of a series of titanium alkoxides. The resultant products were identified as (2MPO)₂Ti(OR)₂ [OR = OCHMe₂ (1), OCH₂CMe₃ (2), OCMe₃ (3)] and [(OR)₂M(μ_c-OBPy)]₃ where MOR = TiOCH₂CMe₃ (4) along with ZrOCMe₃ (5) from Zr(OCMe₃)₄ (μ_c = chelating bridging). The structure of 1–3 were found to adopt similar monomeric structures with octahedrally (Oh) bound Ti metal centers using two terminal OR and two chelating 2MPO derivatives. Switching to the OBPy ligand, cyclic trinuclear species with Oh bound metals that employed two terminal OR and two μ_c-OBPy ligands were isolated. The two rings of the bridging OBPy were rotated such that one O and one N from different rings chelate to a single metal. The synthesis and characterization of these compounds and comparison to appropriate literature species are presented.     

Self-assembly of rectangles and prisms via a molecular "clip"

Aromatic molecular "clips" bearing two symmetrically bound platinum moieties have been prepared. The molecular "clip" 4 readily self-assembled with linear linkers such as 4,4'-bipyridyl, 1,4-bis[2-(4-isocyano-3,5-diisopropylphenyl)ethynyl]benzene, and nicotinic acid to form molecular rectangles. The overall dimensions of the rectangle 7 were 7.3 Angstroms x 15.3 Angstroms. The molecular "clip" also self-assembled with tritopic pyridyl and isocyanide ligands to form trigonal prismatic frameworks. The characterization of the supramolecules by multinuclear NMR, electrospray mass spectrometry, and X-ray crystal structures is also reported.     

NaGe3P3: a new ternary germanium phosphide featuring an unusual [Ge3P7] ring

A new ternary germanium phosphide, NaGe(3)P(3), was obtained for the first time with the use of NaP as the reactive flux. It crystallizes in the orthorhombic space group Pmc2(1). The basic structural unit is an unprecedented [Ge(3)P(7)] ring built from one Ge(P)(4) tetrahedron, one Ge(Ge)(P)(3) tetrahedron and one Ge(Ge)(P)(2) trigonal pyramid with Ge in mixed valences of 4+, 3+ and 1+. The bonding between a tetrahedrally coordinated Ge atom and a trigonal pyramidally coordinated Ge atom (with 4s(2) lone pair of electrons) is observed for the first time in inorganic compounds. These [Ge(3)P(7)] rings are connected with each other to form two-dimensional [Ge(3)P(3)](-) layers separated by Na(+) cations. An optical band gap of 2.06(2) eV was deduced from the diffuse reflectance spectrum. Based on the electronic structure calculation, NaGe(3)P(3) is an indirect gap semiconductor with the Ge 4s, Ge 4p and P 3p orbitals strongly hybridizing around the Fermi level.     

Near-infrared luminescence of nine-coordinate neodymium complexes with benzimidazole-substituted 8-hydroxyquinolines

A new class of benzimidazole-substituted 8-hydroxyquinoline ligands has been prepared that contain a monoanionic tridentate N,N,O-coordinating unit. These ligands form charge-neutral lanthanide complexes of the type [Ln(L-R) 3]. nH 2O or [Ln 2(L2) 3]. nH 2O ( n = 1-3) with early lanthanides from La (III) to Gd (III) inclusive. Crystallographic characterization was carried out for 11 complexes with 6 different ligands. In all of these structures, the lanthanide ion was found to be nine-coordinated by three ligands arranged in an "up-up-down" fashion around the metal center. The coordination environment can be described as a tricapped trigonal prism, with N atoms of quinoline rings occupying capping positions. Upon deprotonation of the ligand and complex formation, a new absorption band appears in the visible range of the spectrum with a maximum in the range of 466-483 nm and molar absorption coefficient of (7.2 - 18) x 10 (3) M (-1) cm (-1). Its origin is likely to be an intraligand phenolate-to-pyridyl charge transfer transition centered on the 8-hydroxyquinolate chromophore. Upon excitation in ligand absorption bands, new Nd (III) complexes display characteristic metal-centered luminescence in the near-infrared region from 850 to 1450 nm with quantum yields and lifetimes in solid state at room temperature as high as 0.34% and 1.2 mus, respectively.     

The role of the π-bonding network for trigonal level splittings of tris-bidentate Cr(acac)3 and Cr(ox) 3 3−

The varying -bonding contributions in the title compounds caused by the different electronic and molecular structure of the chelate rings are used for explaining the large band splittings in the absorption spectra by trigonal symmetry. It is shown that usual ligand field theory and the angular overlap model are not able to account for the trigonal level splitting of Cr(acac)₃ for which the coordination sphere of oxygen atoms is nearly octahedrally arranged. The experimental finding can, however, be rationalized by an extended angular overlap model which considers the phase coupling of -orbitals in the ligands leading to non-additive contributions to the metal-ligand bond energy.On leave of absence from the Bulgarian Academy of Sciences, Sofia, Bulgaria