Density functional theory study of the oxidative dehydrogenation of propane on the (001) surface of V2O5

The density functional theory using a plane‐waves basis set and pseudopotential has been used to study the reaction pathways for ODH of propane on the V₂O₅(001) surface. The calculations indicated that propane adsoprtion step was initiated by the insertion of vanadyl oxygen O (1) into methylene C? H bond forming an iso‐propanol structure. This step is the rate‐determining step with an activation energy of 23.3 kcal/mol. The subsequent step involved the abstraction of the second hydrogen by O (1) site leading the formation of propene. This process had an activation energy of 22.5 kcal/mol. The elimination of surface bound water molecule at the O (1) was a barrierless process. The energy required for this process was compensated from O2 dissociative adsorption. Finally, the electronic density of state has been applied to prove the reality of the calculated results. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Theoretical prediction on HBeN− and HNBe− anions using multiconfiguration second‐order perturbation theory

The HBeN^? and HNBe^? anions have been investigated for the first time using the CASSCF, CASPT2, and DFT/B3LYP methods with the contracted atomic natural orbital (ANO) and cc‐pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO and B3LYP/cc‐pVTZ levels. The ground and the first excited states of HBeN^? are predicted to be X²Π and A²Σ⁺ states, respectively. It was predicted that the ground state of HNBe^? is X²Σ⁺ state. The A²Π state of HNBe^? has unique imaginary frequency. A bend local minimum M1 was found along the 1²A″ potential energy surface and the A²Π state of HNBe^? should be the transition state of the isomerization reactions for M1 ? M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HBeN bond angle. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

The Electropolymerization of 2,6‐Diaminopyridine and Its Application as Mercury Ion Selective Electrode

A composite graphite (CG) electrode modified with poly(2,6‐diaminopyridine) (PDAP) was used as solid state‐ion selective electrode for determination of mercury. The electrooxidation of monomer 2, 6 diaminopyridine (DAP) onto CG was accomplished from the 30 mM DAP in 5% H₂SO₄ and 0.5 M ZnSO₄. The electrode displayed Nernstian response with slope of 28.4±1 mV decade⁻¹ in concentration range of 1×10⁻⁶ to 1×10⁻¹ M and in solution of pH 3–5. The limit of detection for electrode was 3×10⁻⁸ M with response time of 25 s. The electrode was also suitable as an indicator electrode in the potentiometric titration of Hg²⁺ with iodide.     

Structure and Magnetic Properties of Two Lanthanide 1,4‐Phenylenediacetate Compounds

The reactions of Ln(NO₃)₃ with 1,4‐phenylenediacetic acid (H₂PDA) under hydrothermal conditions produced two isostructural lanthanide coordination polymers with the empirical formula [Ln₂(PDA)₃(H₂O)] · 2H₂O [Ln = Nd ( 1 ), Sm ( 2 )]. Single‐crystal X‐ray diffraction analyses revealed that both contain one‐dimensionalmetal carboxylato chains, which are further connected by the–CH₂C₆H₄CH₂– spacers of PDA^2– ligands to yield a three‐dimensional metal‐organic framework. Magnetic susceptibilities of 1 and 2 were measured. The experimental χ_mT value of both compounds decreases continuously with decreasing temperature over the whole temperature range. The best least‐squares fit of the experimental data of 1 to a theoretical equation in the temperature range of 70–300 K gives the zero‐field splitting parameter Δ = 2.21 cm^–1 and the magnetic interaction between the Nd^III ions 2zJ′ = –1.97 cm^–1, which indicates the presence of antiferromagnetic interaction between the Nd^III ions. The experimental χ_mT value of 2 at 2 K is much smaller than the expected value for two free Sm^III ions (⁶H_5/2, g = 2/7) in the ground state, indicating that an antiferromagnetic interaction possibly exists between Sm^III ions at low temperature. Fitting the magnetic data of 2 above 110 K based on an equation deduced from the Sm^III ion in a monomeric system with free‐ion approximation gave a spin‐orbit coupling parameter λ = 192(2) cm^–1     

Transition‐Metal Complexes Based on the 1,3,5‐Triethynyl Benzene Linking Unit

The synthesis of a unique series of heteromultinuclear transition metal compounds is reported. Complexes 1‐I‐3‐Br‐5‐(FcC≡C)‐C₆H₃ ( 4 ), 1‐Br‐3‐(bpy‐C≡C)‐5‐(FcC≡C)‐C₆H₃ ( 6 ), 1,3‐(bpy‐C≡C)₂‐5‐(FcC≡C)‐C₆H₃ ( 7 ), 1‐(XC≡C)‐3‐(bpy‐C≡C)‐5‐(FcC≡C)‐C₆H₃ ( 8 , X = SiMe₃; 9 , X = H), 1‐(HC≡C)‐3‐[(CO)₃ClRe(bpy‐C≡C)]‐5‐(FcC≡C)‐C₆H₃ ( 11 ), 1‐[(Ph₃P)AuC≡C]‐3‐[(CO)₃ClRe(bpy‐C≡C)]‐5‐(FcC≡C)‐C₆H₃ ( 13 ), 1‐[(Ph₃P)AuC≡C]‐3‐(bpy‐C≡C)‐5‐(FcC≡C)‐C₆H₃ ( 14 ), [1‐[(Ph₃PAuC≡C]‐3‐[{[Ti](C≡CSiMe₃)₂}Cu(bpy‐C≡C)]‐5‐(FcC≡C)‐C₆H₃]PF₆ ( 16 ), and [1,3‐[(tBu₂bpy)₂Ru(bpy‐C≡C)]₂‐5‐(FcC≡C)‐C₆H₃](PF₆)₄ ( 18 ) (Fc = (η⁵‐C₅H₄)(η⁵‐C₅H₅)Fe, bpy = 2,2′‐bipyridiyl‐5‐yl, [Ti] = (η⁵‐C₅H₄SiMe₃)₂Ti) were prepared by using consecutive synthesis methodologies including metathesis, desilylation, dehydrohalogenation, and carbon–carbon cross‐coupling reactions. In these complexes the corresponding metal atoms are connected by carbon‐rich bridging units comprising 1,3‐diethynyl‐, 1,3,5‐triethynylbenzene and bipyridyl units. They were characterized by elemental analysis, IR and NMR spectroscopy, and partly by ESI‐TOF mass spectrometry., The structures of 4 and 11 in the solid state are reported. Both molecules are characterized by the central benzene core bridging the individual transition metal complex fragments. The corresponding acetylide entities are, as typical, found in a linear arrangement with representative M–C, C–C_C≡C and C≡C bond lengths.     

Excited‐State Dynamics of the Metal String Complex Co3(dpa)4(NCS)2 from Femtosecond Transient Absorption Spectra

Transient absorption spectroscopy is used to study the excited‐state dynamics of Co₃(dpa)₄(NCS)₂, where dpa is the ligand di(2‐pyridyl)amido. The ππ*, charge‐transfer, and d–d transition states are excited upon irradiation at wavelengths of 330, 400 and 600 nm, respectively. Similar transient spectra are observed under the experimental temporal resolution and the transient species show weak absorption. We thus propose that a low‐lying metal‐centered d–d state is accessed immediately after excitation. Analyses of the experimental kinetic traces reveal rapid conversion from the ligand‐centered ππ* and the charge‐transfer states to this metal‐centered d‐d state within 100 fs. The excited molecule then crosses to a second d–d state within the ligand‐field manifold, with a time coefficient of 0.6–1.4 ps. Because the ground‐state bleaching band recovers with a time coefficient of 10–23 ps, we propose that an excited molecule crosses from the low‐lying d–d state either directly within the same spin system or with spin crossing via the state ²B to the ground state ²A₂ (symmetry group C₄). In this trimetal string complex, relaxation to the ground electronic surface after excitation is thus rapid.     

Time‐dependent density functional theory study on the hydrogen bonding‐induced twisted intramolecular charge‐transfer excited states of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine

In this work, the time‐dependent density functional theory (TDDFT) method was carried out to investigate the hydrogen‐bonded intramolecular charge‐transfer excited state of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine (DMAPIP) in methanol (MeOH) solvent. All the geometric conformations of the ground state and locally excited (LE) state and the twisted intramolecular charge‐transfer (TICT) state for isolated DMAPIP and its hydrogen‐bonded complexes have been optimized. At the same time, the absorption and fluorescence spectra of DMAPIP and the hydrogen‐bonded complexes in different electronic states are also calculated. We theoretically demonstrated for the first time that the intermolecular hydrogen bond formed between DMAPIP and MeOH can induce the formation of the TICT state for DMAPIP in MeOH solvent. Therefore, the two components at 414 and 506 nm observed in the fluorescence spectra of DMAPIP in MeOH solvent were reassigned in this work. The fluorescence peak at 414 nm is confirmed to be the LE state. Furthermore, the red‐shifted shoulder at 506 nm should be originated from the hydrogen‐bonded TICT excited state. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Synthesis and structure of dinuclear dimethylene- or 1,4-phenylene-linked bis(decamethyltitanoceneoxide) (Ti) complexes

The singly tucked-in titanocene [Ti(η⁵-C₅Me₅)(η⁵:η¹-C₅Me₄CH₂)] (1) reacts smoothly with ethylene glycol or hydroquinone to give bis(titanoceneoxide) (Ti^III) complexes [CH₂OTi(η⁵-C₅Me₅)₂]₂ (2) and [(η⁵-C₅Me₅)₂TiOC₆H₄OTi(η⁵-C₅Me₅)₂] (3) containing dimethylene and 1,4-phenylene link, respectively. EPR spectra of 2 in 2-methyltetrahydrofuran glass and 3 in toluene glass revealed that the unpaired d¹ electrons are in interaction to form triplet state molecules. The Ti-Ti distance derived from the zero-field splittings D for the two conformations of 2 (7.42 Å and 7.66 Å) are in good agreement with the Ti-Ti distance of 7.2430(7) Å from the X-ray diffraction single-crystal analysis. For 3, however, the Ti-Ti distance derived from D (7.65 Å) is by 1.47 Å shorter than the crystallographic distance of 9.1230(8) Å that indicates an enhancement of the through-space dipole-dipole interaction due to the presence of a conjugated quinonide link.     

Atomistic in situ investigation of the morphogenesis of grains during pressure-induced phase transitions: molecular dynamics simulations of the B1-B2 transformation of RbCl

The mechanistic details of the pressure-induced B1-B2 phase transition of rubidium chloride are investigated in a series of transition path sampling molecular dynamics simulations. The B2→B1 transformation proceeds by nucleation and growth involving several, initially separated, nucleation centers. We show how independent and partially correlated nucleation events can function within a global mechanism and explore the evolution of phase domains during the transition. From this, the mechanisms of grain boundary formation are elaborated. The atomic structure of the domain-domain interfaces fully support the concept of Bernal polyhedra. Indeed, the manifold of different grain morphologies obtained from our simulations may be rationalized on the basis of essentially only two different kinds of Bernal polyhedra. The latter also play a crucial role for the B1→B2 transformation and specific grain boundary motifs are identified as preferred nucleation centers for this transition.