Density Functional Computational Results Research Articles

Triberyllium cluster sandwich complexes: A density functional investigation

Density functional computational results at the B3LYP/6-311+G∗∗ level of theory for triberyllium–benzene organometallic sandwich complexes are reported. These molecules are the first examples of triangular triberyllium clusters complexed to arene systems. An inverse sandwich complex is reported in which a benzene ring, distorted into a chair conformation, is bound between two eclipsed, triangular Be3 clusters. In addition, a triple-decker complex is reported in which two eclipsed, triangular Be3 clusters are layered between a terminal benzene ring distorted into a boat conformation, a bridging benzene ring also distorted into a boat-like structure, and a terminal benzene ring with a chaise longue conformation. A simple sandwich complex containing a Be3 cluster bound between two distorted benzene rings, one in a boat conformation and the other in a chaise longue conformation, is also reported. The beryllium atoms are asymmetrically bound to the C6H6 rings in η1-, η2-, or η3-modes.

Density Functional Theoretical Modeling, Electrostatic Surface Potential and Surface Enhanced Raman Spectroscopic Studies on Biosynthesized Silver Nanoparticles: Observation of 400 pM Sensitivity to Explosives

Interaction of adsorbate on charged surfaces, orientation of the analyte on the surface, and surface enhancement aspects have been studied. These aspects have been explored in details to explain the surface-enhanced Raman spectroscopic (SERS) spectra of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW or CL-20), a well-known explosive, and 2,4,6-trinitrotoluene (TNT) using one-pot synthesis of silver nanoparticles via biosynthetic route using natural precursor extracts of clove and pepper. The biosynthesized silver nanoparticles (bio Ag Nps) have been characterized using UV-vis spectroscopy, scanning electron microscopy and atomic force microscopy. SERS studies conducted using bio Ag Nps on different water insoluble analytes, such as CL-20 and TNT, lead to SERS signals at concentration levels of 400 pM. The experimental findings have been corroborated with density functional computational results, electrostatic surface potential calculations, Fukui functions and ζ potential measurements.

Dispersion energy enforced dimerization of a cyclic disilylated plumbylene.

By reaction of 1,4-dipotassio-1,1,4,4-tetrakis(trimethylsilyl)tetramethyltetrasilane with PbBr2 in the presence of triethylphosphine a base adduct of a cyclic disilylated plumbylene could be obtained. Phosphine abstraction with B(C6F5)3 led to formation of a base-free plumbylene dimer, which features an unexpected single donor–acceptor PbPb bond. The results of density functional computations at the M06-2X and B3LYP level of theory indicate that the dominating interactions which hold the plumbylene subunits together and which define its actual molecular structure are attracting van der Waals forces between the two large and polarizable plumbylene subunits.

Silaimidazolium and silaimidazolidinium ions

2-Silaimidazolium ions and 2-silaimidazolidinium ions were synthesized by Lewis acid-base adduct formation between N-heterocyclic silylenes and silyl arenium ions. They were isolated in high yields as their [B(C(6)F(5))(4)](-) salts. These salts are stable at room temperature and were characterized by NMR spectroscopy supported by the results of density functional computations of molecular structures and NMR chemical shifts. NICS calculations suggest for the imidazolium ions only a modest degree of aromaticity. Despite the bulkiness of the used substituents R(1) and R(2), silylium ions and behave as classical Lewis pairs and show no unexpected reactivity.

A Joint Experimental and Computational Study on the Electronic Communication in Diethynylaryl‐Bridged (η5‐C5H5)Fe(η2‐dppe) and (η5‐C5H5)Fe(CO)2 Units

AbstractA family of bimetallic complexes [Cp(CO)2Fe–C≡C–Ar–C≡C–Fe(CO)2Cp] {Cp = C5H5; 6a–g: Ar = C4H2S (a), 3‐(C4H9)‐C4HS (b), 3‐(C16H33)‐C4HS (c), C6H4 (d), 2,5‐bis(OC4H9)‐C6H2 (e), 2,5‐bis(OC8H17)‐C6H2 (f), (C6H4)2 (g)} was prepared by the three‐step Pd‐catalysed extended one‐pot (EOP) synthetic protocol from Bu3Sn–C≡CH, X–Ar–X (X = I, Br) and Cp(CO)2FeI. Complexes 6a,d,g were then exposed to ultraviolet irradiation in the presence of an equivalent amount of 1,2‐bis(diphenylphosphanyl)ethane (dppe) to form the corresponding bimetallic complexes [Cp(dppe)Fe–C≡C–Ar–C≡C–Fe(dppe)Cp] (7a,d,g). Compounds 6a–g and 7a,d,g were characterised by cyclic voltammetry (CV). The most significant electrochemical information comes from the oxidation of the dppe derivatives. The ΔE° separations between the subsequent reversible waves suggest that the efficiency of the metal–metal electronic coupling decreases in the order 7a > 7d > 7g. Complexes 7a and 7g were also chemically oxidised with [Fe(Cp*)]2[BF4] {Cp* = C5(CH3)5} and [Fe(Cp)]2[BF4] respectively, and the near infrared (NIR) spectra of the mixed‐valence species 7a+ and 7g+ were recorded. A strong intervalence transition (IT) band was observed only for the radical cation 7a+. While this finding confirms the existence of an electronic interaction between the two termini when a 2,5‐thiophene group is present in the spacer, the NIR spectrum of 7g+ reveals a reduced efficiency in conveying electrons when the C4H2S moiety is replaced by a 4,4′‐biphenyl. In order to rationalise and quantify the extent of electronic communication, ruled by geometrical and electronic factors, density functional computational results on selected [Cp (PH3)2Fe] and [Cp(CO)2Fe] binuclear model complexes are reported. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Optical spectroscopy of jet-cooled NiSi

The electronic states of gaseous diatomic NiSi have been investigated using the combined techniques of resonant two-photon ionization spectroscopy, dispersed fluorescence spectroscopy, and density functional computations. A single electronic band system, designated as the [18.0]1←X 1Σ+ system, has been found in the 17 500–19 500 cm−1 range, and three bands of this system have been rotationally resolved and analyzed. To shorter wavelengths, the spectrum becomes much more congested and intense, and four bands in this region have been rotationally resolved and analyzed as well. A dispersed fluorescence investigation has allowed the measurement of 17 vibrational levels of the ground state. Through this work, the ground state of Ni58Si28 is demonstrated to have Σ+1 symmetry, with r0=2.0316(4) Å, ωe=467.43(30) cm−1, and ωexe=2.046(21) cm−1. These results are in good agreement with the results of density functional computations performed on the ground state. Comparisons to AlCu and CuSi demonstrate that NiSi has a double bond, while these related molecules are best considered as having a single σ-bond.