Geminal Structure Research Articles

Carbene Complexes Based on Dilithium Methandiides

AbstractIn the last 15 years, methandiide ligands have given access to a new class of carbene complexes with unique electronic properties. The metal–carbon interactions in these complexes cover a range of bonding situations, from highly polar interactions to metal–carbon double bonds. This flexibility has allowed the isolation of complexes with metals covering the whole periodic table, including metals that had long been reluctant to form multiple bonds with carbon atoms. Thus, recent years have seen the revelation of many unusual carbene species with interesting reactivities. In this microreview, we focus on the latest developments in the chemistry of methandiides and their use as ligands in carbene complexes. We give an overview of the geminal dianionic compounds, their properties, and molecular and electronic structures, with special focus on those compounds that are applied in transition metal chemistry. The second part of the article deals with the preparation and electronic structures of methandiide‐derived carbene complexes, and we highlight important examples that display the unique properties and efficiency of the ligands. The last section gives an overview of the reactivity and the non‐innocent behavior of these methandiide ligands.

General Synthetic Approach toward Geminal-Substituted Tetraarylethene Fluorophores with Tunable Emission Properties: X-ray Crystallography, Aggregation-Induced Emission and Piezofluorochromism

A general approach to the design and synthesis of a new series of geminal-substituted tetraarylethene (g-TAE) chromophores with aggregation-induced emission (AIE) properties has been developed via Corey–Fuchs reaction and subsequent Suzuki/Stille coupling reactions. To demonstrate the synthetic simplicity and versatility of this approach, fluorophores with diverse electronic characteristics have been synthesized. The validation of the geminal structure and bulky steric effect on the bond lengths and dihedral angles is further confirmed by the X-ray crystallography of three chromophores. With respect to single crystals of 2,2′-(2,2-diphenylethene-1,1-diyl)-dinaphthalene (DPDN2), 1,1′-(2,2-diphenylethene-1,1-diyl)-dinaphthalene (DPDN1), and 9,9′-(2,2-diphenylethene-1,1-diyl)dianthracene (DPDAn), intensive cofacial π–π stacking is absent in their molecular packing. The pseudopolymorphism of DPDAn crystals associated with different photoluminescence properties is investigated. In comparison to the solvent-free DPDAn crystal, the solvated DPDAn with embedded methanol or dichloromethane leads to some non-negligible conformational and packing alterations, which accounts for its distinct fluorescence properties. The AIE phenomena and optical properties of g-TAEs are probed with respect to steric and electronic effects. Along with their electrochemical characteristics and piezofluorochromism, our work has elucidated that this general approach can be utilized to develop a promising class of TAE materials for systematic investigations of its optoelectronic properties and crystal engineering.

Coordination of Two N2 Molecules to One Ni+ Site in Ni–ZSM-5: An FTIR Spectroscopy Study

Ni+ cations were produced in a Ni–ZSM-5 zeolite by partial reduction with CO, and the ability of the Ni+ and Ni2+ sites to coordinate 14N2, 15N2, and/or CO molecules was studied by FTIR spectroscopy. With Ni+ cations, CO produces mono-, di-, and tricarbonyl species while only mono- and dicarbonyls are formed with Ni2+. Adsorption of 14N2 at 100 K results in formation of Ni2+–14N2 adducts (band at 2343 cm–1) and geminal Ni+(14N2)2 complexes (νs at 2287 and νas at 2270 cm–1). The Ni+(14N2)2 complexes lose their ligands stepwise during evacuation at 100 K, and two kinds of monoligand Ni+–14N2 species are formed (2252 and 2238 cm–1). After 15N2 adsorption, the Ni+(15N2)2 complexes were observed at 2211 and 2194 cm–1: the two Ni+–15N2 species at 2178 and 2163 cm–1, and the Ni2+–15N2 adducts at 2264 cm–1. To prove the geminal structure, coadsorption of 14N2 and 15N2 was studied. It resulted in formation of Ni+(14N2)(15N2) species that were characterized by 14N–14N and 15N–15N stretchings at 2277 and 2201 cm–1, ...

Synthesis and reversible hydration–dehydration system of copolymers bearing a vicinal tricarbonyl structure

AbstractNovel copolymers composed of a styrene (St) derivative bearing a vicinal tricarbonyl moiety and various vinyl monomers such as St, methyl methacrylate (MMA), and N‐vinylpyrrolidone (NVP) were synthesized by (1) radical copolymerization of a St derivative with a 1,3‐diketone structure with St, MMA, and NVP and (2) successive oxidation of the resulting copolymers with N‐bromosuccinimide in DMSO to convert their 1,3‐diketone moieties in the side chains into the corresponding vicinal tricarbonyl moieties. Their tricarbonyl moieties were readily hydrated in water‐containing acetone to generate the corresponding copolymers bearing geminal diol structures in the side chains. On the other hand, heating the resulting copolymers bearing the geminal diol structures in vacuo‐enabled successful recovery of the vicinal tricarbonyl moieties to demonstrate the reversible nature of this system. The hydration behavior in powdery state under air atmosphere saturated by water was also investigated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

On the Exception to the /υ/ to /A/ Change in Early Modern English

Chung, Inkie. 2012. On the Exception to the /υ/to/A/ Change in Early Modern English. The Linguistic Association of Korea Journal, 20(3), 39~58, This paper deals with an exception of the diachronic change in the history of the English language, i.e., the change of the short high back (lax) rounded vowel /υ/ in Middle English to the mid back/central lax unrounded vowel /A/in Modern English. This exception is best analyzed as the inalterability effect of partial geminate structure (in the sense of Hayes, 1986) due to spreading of the [labial] node of the preceding labial consonant to the following vowel. It provides support for Halle, Vaux and Wolfe`s (2000) revised articulator model, contra Clements` (1991) unified feature model. It also presents arguments supporting Halle, Vaux and Wolfe`s (2000) claim that only terminal features spread in the geometrical representation of distinctive features. The analysis employs Calabrese`s (2005) correlation statement and the notion of economy (Chomsky, 2000; Calabrese, 2005).

CO oxidation by co-adsorbed atomic O on the Au(321) surface with Ag impurities: A mechanistic study from first-principles calculations

The reaction routes between co-adsorbed CO and O on kinked Au(321) slabs are analyzed theoretically. Complexes of vicinal type react most easily with calculated barriers from 0.05 to 0.3eV, whereas the more strongly co-adsorbed geminal structures do not react directly unless surface oxygen is present in excess. Generally, the activation energy of CO2 formation from vicinal complexes remains low and that from geminal complexes increases, when Ag impurities are introduced. Our results can be generalized to other rough gold surfaces, particularly, helping to understand the formation of CO2 above 200K, as observed in the temperature programmed desorption studies of nanoporous gold, a monolithic nanostructured gold catalyst.

Construction of reversible hydration–dehydration system by a model compound and a novel polymer bearing vicinal tricarbonyl structure

AbstractA novel polymer bearing acyclic vicinal tricarbonyl moieties in the side chains was synthesized by (1) radical polymerization of a styrene derivative with a 1,3‐diketone structure and (2) successive treatment of the resulting polystyrene derivative by N‐bromosuccinimide to convert its 1,3‐diketone moiety in the side chains into the corresponding vicinal tricarbonyl moiety. The tricarbonyl moiety was highly reactive with water to permit its rapid conversion into a geminal diol structure in water‐containing acetone. On the other hand, heating the resulting polymer bearing the geminal diol structure under vacuum enabled successful recovery of the vicinal tricarbonyl moiety to demonstrate the reversible nature of this system, which allowed us to repeat the hydration–dehydration cycle without deteriorating the polymer structure. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Geminate template: A model for first Finnish words

The CV syllable or reduplicative word is seen as an essential structure in early speech development, and word-initial consonants are seen to be a part of the optimal syllable in the speech of young children. The aim of this study is to evaluate the usefulness of the CV(CV) structure for a description of the first words of Joel (1;1—1;6), who is acquiring Finnish. Among his first 50 words, many words were produced with a (C)VC:V structure instead of a CVCV structure. An overused geminate template gives support for the saliency of the medial position. The saliency of the medial position is supported by the fact that word-initial consonant omission is common in the speech of Finnish children despite the word stress being on the first syllable. Additional support comes from the reduction of Finnish three-syllable words. Even though a reduced word usually consists of the first two syllables (SW1), a geminate structure may become part of the word regardless of its location in the word.

Combining explicitly correlated R12 and Gaussian geminal electronic structure theories

Explicitly correlated R12 methods using a single short-range correlation factor (also known as F12 methods) have dramatically smaller basis set errors compared to the standard wave function counterparts, even when used with small basis sets. Correlations on several length scales, however, may not be described efficiently with one correlation factor. Here the authors explore a more general MP2-R12 method in which each electron pair uses a set of (contracted) Gaussian-type geminals (GTGs) with fixed exponents, whose coefficients are optimized linearly. The following features distinguish the current method from related explicitly correlated approaches published in the literature: (1) only two-electron integrals are needed, (2) the only approximations are the resolution of the identity and the generalized Brillouin condition, (3) only linear parameters are optimized, and (4) an arbitrary number of (non-)contracted GTGs can appear. The present method using only three GTGs and a double-zeta quality basis computed valence correlation energies for a set of 20 small molecules only 2.2% removed from the basis set limit. The average basis set error reduces to 1.2% using a near-complete set of seven GTGs with the double-zeta basis set. The conventional MP2 energies computed with much larger quadruple, quintuple, and sextuple basis sets all had larger average errors: 4.6%, 2.4%, and 1.5%, respectively. The new method compares well to the published MP2-R12 method using a single Slater-type geminal (STG) correlation factor. For example, the average basis set error in the absolute MP2-R12 energy obtained with the exp(-r12) correlation factor is 1.7%. Correlation contribution to atomization energies evaluated with the present method and with the STG-based method only required a double-zeta basis set to exceed the precision of the conventional sextuple-zeta result. The new method is shown to always be numerically stable if linear dependencies are removed from the two-particle basis and the zeroth-order Hamiltonian matrix is made positive definite.

Density Functional Theory Studies on Transimination of Vitamin B6 Analogues through Geminal Diamine Formation

A theoretical study on the transimination reaction in the gas phase of a molecular complex that consists of a Schiff base formed from a vitamin B6 model compound, methylamine, and one water molecule is reported. In this nonenzymatic environment, DFT calculations (B3LYP/6-31+G*) with full optimization of each intermediate and transistion state structure and a further study of the topology of the charge density function according to Bader's AIM theory are carried out. This work has allowed the detailed outline of the energy profile of the reaction leading to the geminal diamine formation and the description of the geometries of all the structures involved. The reaction determining step is the addition of the incoming amine onto the Schiff base and the main intermediate of the overall reaction is a geminal diamine structure. The mechanism also points out the reactive role of one water molecule by allowing the proton transfer between distant sites of the molecular complex by means of the formation of a concerted transition state.

Hydrogen adsorption on Cs thin films deposited on Al(111)

The adsorption of hydrogen on Cs thin films deposited on Al(111) has been investigated by means of electron energy loss spectroscopy (EELS) and temperature programmed desorption (TPD). When hydrogen is adsorbed at a surface temperature of 85 K, three hydride phases are formed depending on Cs coverage. For Cs coverages below one monolayer (ML), hydrogen adsorption causes formation of a stable surface complex, CsAlH 2, in which H atoms are bound to Al with a geminal structure. In the coverage range between 1 and 2 ML, a surface hydride of Cs and the CsAlH 2 complex are formed on the surface, while above 2 ML, both the surface hydride and a bulk hydride of Cs are formed. When a hydrogen-adsorbed thick Cs film is heated from 85 K, Cs atoms start to desorb from 270 K, while hydrogen atoms initially located in surface region do not desorb with Cs but penetrate into bulk and finally reach the Al substrate resulting in the formation of the CsAlH 2 complex. This complex is quite stable and decomposes above 450 K desorbing H 2 and Cs. Hydrogen adsorption on CsAl surface alloy phases was also studied and it was found that its adsorption state is essentially the same as that on the Cs submonolayer overlayers, that is, formation of the CsAlH 2 complex.

Stabilized hydrogen on Cs-modified Al(111): Evidence for formation of alkali aluminum dihydride surface complex

The adsorption of hydrogen on Cs-modified Al(111) surfaces has been studied using high-resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). A stabilized hydrogen species which desorbs simultaneously with Cs at 480 K (γ hydrogen) appears in the presence of Cs and the ratio between the number of Cs and that of the γ hydrogen is 1:2, independent of Cs coverage, which is indicative of a substantial attractive interaction between Cs and the γ hydrogen. HREEL spectra of the γ hydrogen exhibit intense loss peaks at around 800 and 1700 cm−1. Detailed analyses of these loss peaks using isotope mixtures (H+D) indicate that the γ hydrogen is directly bound to Al with a geminal structure (AlH2). From the combined results of TPD and HREELS, it is considered that a cesium aluminum dihydride complex (CsAlH2) is formed on the surface, which is supported by ab initio calculations.

Preparation of urethane and urea derivatives of (NPCl2)3. Crystal structure of a spirocyclic phosphazene with a phosphacyanuric loop

Reactions of (NPCl2)3 with NaNCO in the presence of aliphatic alcohols have been investigated. Using an equimolar amount of NaNCO in refluxing acetonitrile, high yields of mono(urethane) derivatives N3P3Cl5(NHCO2R) were obtained. Disubstitution is mainly non-geminal. Reactions of (NPCl2)3 with AgNCO and methanol in acetonitrile follow a quite different pattern and lead to the formation of three products with basically geminal structures, e.g. gem-N3P3Cl4(OR)(NHCO2R), gem-N3P3Cl4(NHCO2R)2, and a spiro derivative (NPCl2)2NP[N(CO2R)C(O)NHC(CH3)N]. The crystal structure of the last compound (R = CH3) has been determined. The difference between the reaction pathways observed for NaNCO and AgNCO is discussed in terms of SN2 and SN1 mechanisms, respectively. An improved synthesis of (NPCl2)2NP(NH2)(NCO) and its reactions with alcohols and amines are described.

Complexation of dihydropyridine derivatives with cyclodextrins and 2-hydroxypropyl-β-cyclodextrin in solution

Structure-interaction relationships in the inclusion complexation of cyclodextrins (CD) and 2-hydroxypropyl β-cyclodextrin (2-HP-β-CD) with homologous derivatives of 1,4-dihydropyridines (DHPs) were investigated on the basis of phase solubility analysis, stabilization effects, and 1H-NMR spectroscopy. Furthermore, the influence of 2-HP-β-CD on the adsorption of DHPs into the administration set and the compatibility of the complex with excipients for intravenous administration was examined. The interaction of DHPs with CD decreased in the order β-CD > 2-HP-/3-CD > γ-CD > α-CD. The solubilization of DHP derivatives with 2-HP-β-CD was strongly influenced by the pH and the counterion indicating a considerable influence of the degree of dissociation of the guest molecule on complex formation. DHP derivatives with aromatic substitution were much more strongly solubilized than alkyl esters such as nitrendipine. It was found that the intensity of interaction of 2-HP-β-CD with DHPs depends on the substituents in the aromatic side chain decreasing in the order chlorobenzyl substitution, linear monoaryl structures, and geminal diaryl structures. Aromatically substituted 4-(3-nitrophenyl)-DHP derivatives were found to be photolabile, however, no photostabilization was observed with 2-HP-β-CD. Concerning the chemical stability of DHP derivatives, 2-HP-β-CD exerted destabilizing effects. By means of 1H-NMR chemical shift measurement with the respective aromatic amines, the inclusion of the aromatic ester side chain within the cavity of 2-HP-β-CD was elucidated in aqueous solution. The adsorption of DHPs on hydrophobic PVC administration tubes was significantly reduced due to complexation with 2-HP-β-CD. The addition of human albumin led to complete recovery of the drug. The compatibility of the complexes with solutions for infusion was generally improved compared with conventionally solubilized systems, and increased in the order modified gelatin, bovine serum, physiological NaCl, dextran, and carbohydrates such as hexoses or sugar alcohols.

In search of Trigeminal Pentafluorosulfanyl (SF 5) carbon derivatives

In the course of our studies to synthesize as yet unknown perfluorocarbon compounds containing three SF 5, R fSF 4, or SF 5 and R fSF 4 groups, all attached to the same carbon atom, we have investigated the fluorination behavior of promising starting materials using different fluorination techniques like elemental as well as electrochemical methods. H 2C(SCH 3) 2 (1) HC(SCH 3) 3 (2) HC(SH) 3 (3) HC(SAc) 3 (4) Hexathiaadamantane (5) Trimethylhexathiaadamantane (6) In compounds 26, the tertiary carbon-sulfur structure is already present and has to survive the fluorination processes without complete degradation by cleavage of one of the carbon-sulfur bonds. Meanwhile, in compound 1 such a tertiary structure has to be formed during the fluorination via the cleavage of a CS bond at one molecule, followed by the formation of a third CS bond at the starting CS geminal structure of another molecule. Such a “cleavage — new bond formation” phenomenon is a well-known experimental observation, especially during the electrochemical fluorination process. The results of the fluorinations of compounds 16 will be discussed in detail.

ChemInform Abstract: An Investigation of the Reaction Products of N3P3Cl4(NH2)2 with Nucleophilic Reagents. Examples of Geminal→Non‐Geminal Rearrangements

Abstract Based on its reactions with various nucleophiles both geminal and non-geminal structures have been earlier proposed for N3P3Cl4(NH2)2, although its geminal structure is now considered established. The reactions of this compound with alcohols have been investigated and the products examined by NMR spectroscopy and X-ray crystallography. Evidence for both unrearranged as well as geminal → non-geminal rearranged alcoholysis products is presented.

AN INVESTIGATION OF THE REACTION PRODUCTS OF N3P3CL4(NH2)2WITH NUCLEOPHILIC REAGENTS. EXAMPLES OF GEMINAL → NON-GEMINAL REARRANGEMENTS

Abstract Based on its reactions with various nucleophiles both geminal and non-geminal structures have been earlier proposed for N3P3Cl4(NH2)2, although its geminal structure is now considered established. The reactions of this compound with alcohols have been investigated and the products examined by NMR spectroscopy and X-ray crystallography. Evidence for both unrearranged as well as geminal → non-geminal rearranged alcoholysis products is presented.

Studies of phosphazenes—VII: Reactions of hexabromocyclotriphosphazatirene, N 3P 3Br 6, with ethylamine

The reaction of hexabromocyclotriphosphazene, N 3P 3Br 6 with ethylamine yields the derivatives N 3P 3Br 6− n (NHEt) n [ n = 1, 2(two isomers), 4 and 6]. Two hydrogen bromide adducts, N 3P 3Br 2(NHEt) 4·HBr and N 3P 3(NHEt) 6·HBr have also been isolated. The 1H NMR data indicate that the bis-derivatives have nongeminal structures whereas the tetrakis-compound possesses a geminal structure. For the hydrogen bromide adducts, infrared and 1H NMR spectroscopic data suggest that protonation occurs at a ring nitrogen atom. The halogen replacement pattern is very similar to that observed in the analogous reaction of hexachlorocyclotriphosphazene, N 3P 3Cl 6.

The preparation and geminal molecular structure of the compound N 3P 3Br 4(NH 2) 2

1,1-Diamido-3,3,5,5-tetrabromocyclotriphosphonitrile, N 3P 3Br 4(NH 2) 2, was prepared by allowing the trimeric bromide, N 3P 3Br 6, to react with ammonia in diethyl ether. The compound was characterized by i.r. spectroscopy and mass spectrometry. Phosphorus-31 NMR spectroscopy indicated a geminal molecular structure. The molecular structure of the compound N 3P 3Br 4(NH 2) 2 was compared with that of the corresponding chloride to determine whether the same substitution pattern is followed in its formation.

The geminal molecular structure of the compound N 3P 3Cl 4(NCS) 2

The compound, N 3P 3Cl 4(NCS) 2, was prepared and characterized by i.r., mass and 31P NMR spectroscopy. I.R. data indicated that each thiocyanate moiety is nitrogen-bonded to a phosphorus atom in the ring. A geminal molecular structure was assigned on the basis of 31P NMR data. Several alcohol and amine addition derivatives of the compound gem-N 3P 3Cl 4(NCS) 2 were also prepared. The addition compounds were characterized by infrared and 31P NMR spectroscopy. Geminal molecular structures were assigned to these adducts on the basis of their 31P NMR spectra.