Resonance energies of fullerenes with 4-membered rings

We report the resonance energies (REs ) of several fullerenes with 4-membered rings and their isomers with only 5- and 6-membered rings computed using the conjugated-circuit model [RE (CC )] and the topological resonance energy (TRE ) model. Both aromaticity indices were normalized by dividing by the size of the considered fullerene [RE (CC )/e and TRE /e]. The results parallel the predictions by Gao and Herndon using the much more advanced SCF –UHF π-electron approach. A good linear correlation is found between the topologically defined indices [RE (CC )/e and TRE /e] and normalized SCF –UHF π-electron energy. © 1995 John Wiley & Sons, Inc.     

Nearly Degenerate Isomers of C(BH)2: Cumulene,Carbene, or Carbone?

The ground electronic state of C(BH)₂ exhibits both a linear minimum and a peculiar angle‐deformation isomer with a central B‐C‐B angle near 90°. Definitive computations on these species and the intervening transition state have been executed by means of coupled‐cluster theory including single and double excitations (CCSD), perturbative triples (CCSD(T)), and full triples with perturbative quadruples (CCSDT(Q)), in concert with series of correlation‐consistent basis sets (cc‐pVXZ, X=D, T, Q, 5, 6; cc‐pCVXZ, X=T, Q). Final energies were pinpointed by focal‐point analyses (FPA) targeting the complete basis‐set limit of CCSDT(Q) theory with auxiliary core correlation, relativistic, and non‐Born–Oppenheimer corrections. Isomerization of the linear species to the bent form has a minuscule FPA reaction energy of 0.02 kcal mol^?1 and a corresponding barrier of only 1.89 kcal mol^?1. Quantum tunneling computations reveal interconversion of the two isomers on a timescale much less than 1 s even at 0 K. Highly accurate CCSD(T)/cc‐pVTZ and composite c～CCSDT(Q)/cc‐pCVQZ anharmonic vibrational frequencies confirm matrix‐isolation infrared bands previously assigned to linear C(BH)₂ and provide excellent predictions for the heretofore unobserved bent isomer. Chemical bonding in the C(BH)₂ species was exhaustively investigated by the atoms‐in‐molecules (AIM) approach, molecular orbital plots, various population analyses, local mode vibrations and force constants, unified reaction valley analysis (URVA), and other methods. Linear C(BH)₂ is a cumulene, whereas bent C(BH)₂ is best characterized as a carbene with little carbone character. Weak B–B attraction is clearly present in the unusual bent isomer, but its strength is insufficient to form a CB₂ ring with a genuine boron–boron bond and attendant AIM bond path.     

arachno-Diazapentaboranes

The reaction of appropriate amounts of BH₃ with diazadiboretidines (RBNtBu)₂ ( 1a–e ; R = Et, Pr, Bu, tBu, tBu(Me₃Si)N) transforms them into cyclic diazapentaboranes either of the type [ RB (H₂) BR NtBu BH NtBu ] ( 2a–c ), of the type [ HB (H₂) BR NtBu BH NtBu ] ( 3a–d ), or of the type [ HB (H₂) BH NtBu BH NtBu ] ( 4 ), or into an acyclic product RBH NtBu BH NtBu BHR ( 2e ). The structure of 3c is characterized by a planar N₂B₃ ring skeleton with an unsymmetrical double-hydrogen bridge.     

A Quasi-lattice Theory for Compound Forming Molten Alloys

Abstract

The complex formation model of Bhatia and Hargrove (BH) to explain the thermodynamic properties of compound forming A-B alloys is reformulated using a quasi-lattice picture. The formulation is explicitly carried out to an approximation where the pseudo-ternary alloy (of A and B atoms and A_μB_ν complexes (μ, ν small integers)), envisaged in BH, is treated in the quasi-chemical approximation. It is advantageous over BH in two major respects: Firstly, it gives useful insight into the two approximations used in BH, since these follow from it by simply going to a lower (zeroth) approximation and setting the coordination number z of the alloy to be z = 2 and z = ∞. Secondly, unlike the BH approach, it provides also an expression for the short range order parameter α₁ for nearest neighbours. The effect of varying z in the formulae is examined and a brief discussion of α₁ is given.     

Ab Initio spectroscopic characterization of borane,BH, in its electronic state

The accurate potential energy and electric dipole moment functions of borane, BH, in its electronic state have been determined from ab initio calculations using the multireference averaged coupled‐pair functional method in conjunction with the correlation‐consistent core‐valence basis sets up to septuple‐zeta quality. The higher‐order electron correlation, scalar relativistic, adiabatic, and nonadiabatic effects were discussed. Vibration‐rotation energy levels of the ¹¹BH, ¹¹BD, ¹⁰BH, and ¹⁰BD isotopologues were predicted to near “spectroscopic” accuracy. For the main isotopologue ¹¹BH, the adiabatic dissociation energy D₀ and the effective equilibrium internuclear distance r_e were predicted to be 28 469 ± 10 cm^?1 and 1.23214 ± 0.0001 Å, respectively. © 2015 Wiley Periodicals, Inc.     

Synthesis,crystal structures and chemical bonding of RE5−xLixGe4 (RE = Nd,Sm and Gd; x≃ 1) with the orthorhombic Gd5Si4 type

The syntheses and single‐crystal and electronic structures of three new ternary lithium rare earth germanides, RE_5−xLi_xGe₄ (RE = Nd, Sm and Gd; x≃ 1), namely tetrasamarium lithium tetragermanide (Sm_3.97Li_1.03Ge₄), tetraneodymium lithium tetragermanide (Nd_3.97Li_1.03Ge₄) and tetragadolinium lithium tetragermanide (Gd_3.96Li_1.03Ge₄), are reported. All three compounds crystallize in the orthorhombic space group Pnma and adopt the Gd₅Si₄ structure type (Pearson code oP36). There are six atoms in the asymmetric unit: Li1 in Wyckoff site 4c, RE1 in 8d, RE2 in 8d, Ge1 in 8d, Ge2 in 4c and Ge3 in 4c. One of the RE sites, i.e. RE2, is statistically occupied by RE and Li atoms, accounting for the small deviation from ideal RE₄LiGe₄ stoichiometry.     

Cyanohydridoborate Anions: Synthesis,Salts, and Low-Viscosity Ionic Liquids

High-yield syntheses up to molar scales for salts of [BH(CN)₃]⁻ ( 2 ) and [BH₂(CN)₂]⁻ ( 3 ) starting from commercially available Na[BH₄] (Na 5 ), Na[BH₃(CN)] (Na 4 ), BCl₃, (CH₃)₃SiCN, and KCN were developed. Direct conversion of Na 5 into K 2 was accomplished with (CH₃)₃SiCN and (CH₃)₃SiCl as a catalyst in an autoclave. Alternatively, Na 5 is converted into Na[BH{OC(O)R}₃] (R=alkyl) that is more reactive towards (CH₃)₃SiCN and thus provides an easy access to salts of 2 . Some reaction intermediates were identified, for example, Na[BH(CN){OC(O)Et}₂] (Na 7 b ) and Na[BH(CN)₂{OC(O)Et}] (Na 8 b ). A third entry to 2 and 3 uses ether adducts of BHCl₂ or BH₂Cl such as the commercial 1,4-dioxane adducts that react with KCN and (CH₃)₃SiCN. Alkali metal salts of 2 and 3 are convenient starting materials for organic salts, especially for low viscosity ionic liquids (ILs). [EMIm] 3 has the lowest viscosity and highest conductivity with 10.2 mPa s and 32.6 mS cm⁻¹ at 20 °C known for non-protic ILs. The ILs are thermally, chemically, and electrochemically robust. These properties are crucial for applications in electrochemical devices, for example, dye-sensitized solar cells (Grätzel cells).     

Dividing a complex reaction involving a hypervalent iodine reagent into three limiting mechanisms by ab initio molecular dynamics

The electrophilic N‐trifluoromethylation of MeCN with a hypervalent iodine reagent to form a nitrilium ion, that is rapidly trapped by an azole nucleophile, is thought to occur via reductive elimination (RE). A recent study showed that, depending on the solvent representation, the S_N2 is favoured to a different extent over the RE. However, there is a discriminative solvent effect present, which calls for a statistical mechanics approach to fully account for the entropic contributions. In this study, we perform metadynamic simulations for two trifluoromethylation reactions (with N‐ and S‐nucleophiles), showing that the RE mechanism is always favoured in MeCN solution. These computations also indicate that a radical mechanism (single electron transfer) may play an important role. The computational protocol based on accelerated molecular dynamics for the exploration of the free energy surface is transferable and will be applied to similar reactions to investigate other electrophiles on the reagent. Based on the activation parameters determined, this approach also gives insight into the mechanistic details of the trifluoromethylation and shows that these commonly known mechanisms mark the limits within which the reaction proceeds. © 2015 Wiley Periodicals, Inc.     

New Trinuclear Complexes of Group 6, 8, and 9 Metals with a Triply Bridging Borylene Ligand

Trinuclear complexes of group 6, 8, and 9 transition metals with a (μ₃‐BH) ligand [(μ₃‐BH)(Cp*Rh)₂(μ‐CO)M′(CO)₅], 3 and 4 ( 3 : M′=Mo; 4 : M′=W) and 5 – 8 , [(Cp*Ru)₃(μ₃‐CO)₂(μ₃‐BH)(μ₃‐E)(μ‐H){M′(CO)₃}] ( 5 : M′=Cr, E=CO; 6 : M′=Mo, E=CO; 7 : M′=Mo, E=BH; 8 : M′=W, E=CO), have been synthesized from the reaction between nido‐[(Cp*M)₂B₃H₇] (nido‐ 1 : M=Rh; nido‐ 2 : M=RuH, Cp*=η⁵‐C₅Me₅) and [M′(CO)₅ ? thf] (M′=Mo and W). Compounds 3 and 4 are isoelectronic and isostructural with [(μ₃‐BH)(Cp*Co)₂(μ‐CO)M′(CO)₅], (M′=Cr, Mo and W) and [(μ₃‐BH)(Cp*Co)₂(μ‐CO)(μ‐H)₂M′′H(CO)₃], (M′′=Mn and Re). All compounds are composed of a bridging borylene ligand (B?H) that is effectively stabilized by a trinuclear framework. In contrast, the reaction of nido‐ 1 with [Cr(CO)₅ ? thf] gave [(Cp*Rh)₂Cr(CO)₃(μ‐CO)(μ₃‐BH)(B₂H₄)] ( 9 ). The geometry of 9 can be viewed as a condensed polyhedron composed of [Rh₂Cr(μ₃‐BH)] and [Rh₂CrB₂], a tetrahedral and a square pyramidal geometry, respectively. The bonding of 9 can be considered by using the polyhedral fusion formalism of Mingos. All compounds have been characterized by using different spectroscopic studies and the molecular structures were determined by using single‐crystal X‐ray diffraction analysis.     

A Series of Rare-Earth Mesoionic Carbene Complexes

We report the synthesis and characterisation of a series of rare-earth mesoionic carbene complexes, [RE{N(SiMe₃)₂}₃{CN(Me)C(Me)N(Me)CH}] ( 3RE , RE=Sc, Ce, Pr, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), greatly expanding the limited library of f-block mesoionic carbene complexes. These complexes were prepared by treatment of the parent RE-triamides with an N-heterocyclic olefin (NHO), where an NHO backbone proton undergoes a formal 1,4-proton migration to the NHO-methylene group. For all RE(III) metals, as expected, quantum chemical calculations suggest only a σ-component to the metal−carbene bonding, in contrast to a previously reported uranium(III) congener where the 5f³ metal engages in a weak π-back-bond to the MIC. All complexes were characterised by static variable-temperature magnetic measurements, and dynamic magnetic measurements reveal that 3Dy and 3Er are field-induced single-molecule magnets (SMMs), with U_eff energy barriers of 35 and 128 K, respectively. Complex 3Dy is, as expected, a poorly performing SMM, but conversely 3Er performs unexpectedly well.     

Syntheses,structures and catalytic activities of low-coordinated rare-earth metal complexes containing 2,2′-pyridylpyrrolides

Reactions of the ligand precursors 2-(2′-pyridyl)-3,5-Me₂-pyrrole ( L ¹ H) and 2-(2-pyridyl)-3,4,5-Me₃-pyrrole ( L ² H) with [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ in toluene afforded a series of low-coordinated rare-earth metal bis-amido complexes L ¹ RE[N(SiMe₃)₂]₂ [RE = Y ( 1a ), Dy ( 1b ), Er ( 1c ), Yb ( 1d )] and L ² RE[N(SiMe₃)₂]₂ [RE = Y ( 2a ), Dy ( 2b ), Er ( 2c ), Yb ( 2d )]. With the ionic radius of rare-earth metal increasing, the reaction of L ¹ H and [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ gave dinuclear complexes ( L ¹ )₂RE(μ-Cl)(μ-η⁵:η¹:η¹- L ¹ )RE( L ¹ )[N(SiMe₃)₂]₂ [RE = Sm ( 1e ), Pr ( 1f )]; however, the reaction of L ² H and [(Me₃Si)₂N]₃Sm(μ-Cl)Li(THF)₃ afforded ( L ² )₂Sm[N(SiMe₃)₂]₂ ( 2e ). Results indicated that the ionic radius of rare-earth metal and subtle change in the ligands have substantial effects on the structure and bonding mode of complexes. The complexes showed a high catalytic activity for the ring-opening reaction of cyclohexene oxide with amines to afford various β-aminoalcohols under mild solvent-free conditions.     

Ring opening polymerization of α‐amino acid N‐carboxyanhydrides catalyzed by rare earth catalysts: Polymerization characteristics and mechanism

Five rare earth complexes are first introduced to catalyze ring opening polymerizations (ROPs) of γ‐benzyl‐L ‐glutamate N‐carboxyanhydride (BLG NCA) and L ‐alanine NCA (ALA NCA) including rare earth isopropoxide (RE(OiPr)₃), rare earth tris(2,6‐di‐tert‐butyl‐4‐methylphenolate) (RE(OAr)₃), rare earth tris(borohydride) (RE(BH₄)₃(THF)₃), rare earth tris[bis(trimethylsilyl)amide] (RE(NTMS)₃), and rare earth trifluoromethanesulfonate. The first four catalysts exhibit high activities in ROPs producing polypeptides with quantitative yields (>90%) and moderate molecular weight (MW) distributions ranging from 1.2 to 1.6. In RE(BH₄)₃(THF)₃ and RE(NTMS)₃ catalytic systems, MWs of the produced polypeptides can be controlled by feeding ratios of monomer to catalyst, which is in contrast to the systems of RE(OiPr)₃ and RE(OAr)₃ with little controllability over the MWs. End groups of the polypeptides are analyzed by MALDI‐TOF MS and polymerization mechanisms are proposed accordingly. With ligands of significant steric hindrance in RE(OiPr)₃ and RE(OAr)₃, deprotonation of 3‐NH of NCA is the only initiation mode producing a N‐rare earth metallated NCA ( i ) responsible for further chain growth, resulting in α‐carboxylic‐ω‐aminotelechelic polypeptides after termination. In the case of RE(BH₄)₃(THF)₃ with small ligands, another initiation mode at 5‐CO position of NCA takes place simultaneously, resulting in α‐hydroxyl‐ω‐aminotelechelic polypeptides. In RE(NTMS)₃ system, the protonated ligand hexamethyldisilazane (HMDS) initiates the polymerization and produces α‐amide‐ω‐aminotelechelic polypeptides. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A comparative study of effective core potential and full-electron calculations in Mo compounds. I. An analysis of topological properties of bond charge distribution

Effective core potential (ECP) and full-electron (FE) calculations for MoS₄^?2, MoO₄^?2, and MoOCl₄ compounds were analyzed. Geometry parameters, binding energies, charge distributions, and topological properties of the electronic density were studied for Mo? L bonds (L = S, O, Cl). Results clearly indicate that those approaches that include valence plus 4s and 4p electrons (ECP2 methods) are able to reproduce the topological properties of Mo? L bonds, charge distributions, and geometries with respect to those obtained by FE methods. ECP methods that consider only the 4d and 5s valence electrons (ECP1) fail in the calculation of molecular properties. The use of 5p functions in ECP1 approaches produces a negative Mulliken charge on Mo. Bader's charges give more consistent results than Mulliken's ones. A new parameter for measuring the degree of ionicity is proposed. © 1994 by John Wiley & Sons, Inc.     

The role of kinetic energy in chemical binding

The wavefunctions and various partitions of the energy are examined for a variety of small molecules (H₂, H₃, H₄, HeH, HeH₂, He₂, LiH, and BH) in order to isolate the factors crucial for bond formation. We find that a natural partition of the energy leads to the conclusion that the crucial factor is the exchange, or nonclassical, part of the kinetic energy, T ^x. The change in T ^xupon pushing the atoms towards one another is the dominant term in the binding energy; it is negative when the resulting molecule is stable and positive when it is unstable. We show that T ^x is related to the interference kinetic energy considered by Ruedenberg.

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Zusammenfassung Die Wellenfunktionen und verschiedene Zerlegungen der Energie werden für eine Reihe kleiner Moleküle untersucht (H₂, H₃, H₄, HeH, HeH₂, He₂, LiH und BH), um die Faktoren zu finden, die für die Bindungsbildung ausschlaggebend sind. Die natürliche Zerlegung der Energie läßt die Folgerung zu, daß der bestimmende Faktor der Austauschanteil T ^x(oder nichtklassische Anteil) der kinetischen Energie ist. Die Änderung von T ^xbeim Zusammenführen der Atome ist der dominierende Term für die Bindungsenergie; er ist negativ, wenn das resultierende Molekül stabil ist, und positiv, falls es instabil ist. Es wird gezeigt, daß T ^x im Zusammenhang zum Wechselwirkungsanteil der kinetischen Energie nach Ruedenberg steht.

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Partially supported by a grant (GP-15423) from the National Science Foundation. This paper is based on a portion of the PhD thesis (California Institute of Technology, 1970) by CWW.

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National Science Foundation Predoctoral Trainee.

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Alfred P. Sloan Foundation Research Fellow.

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Contribution No. 3917.     

Heterometallic Triply‐Bridging Bis‐Borylene Complexes

Triply‐bridging bis‐{hydrido(borylene)} and bis‐borylene species of groups 6, 8 and 9 transition metals are reported. Mild thermolysis of [Fe₂(CO)₉] with an in situ produced intermediate, generated from the low‐temperature reaction of [Cp*WCl₄] (Cp*=η⁵‐C₅Me₅) and [LiBH₄?THF] afforded triply‐bridging bis‐{hydrido(borylene)}, [(μ₃‐BH)₂H₂{Cp*W(CO)₂}₂{Fe(CO)₂}] ( 1 ) and bis‐borylene, [(μ₃‐BH)₂{Cp*W(CO)₂}₂{Fe(CO)₃}] ( 2 ). The chemical bonding analyses of 1 show that the B?H interactions in bis‐{hydrido (borylene)} species is stronger as compared to the M?H ones. Frontier molecular orbital analysis shows a significantly larger energy gap between the HOMO‐LUMO for 2 as compared to 1 . In an attempt to synthesize the ruthenium analogue of 1 , a similar reaction has been performed with [Ru₃(CO)₁₂]. Although we failed to get the bis‐{hydrido(borylene)} species, the reaction afforded triply‐bridging bis‐borylene species [(μ₃‐BH)₂{WCp*(CO)₂}₂{Ru(CO)₃}] ( 2′ ), an analogue of 2 . In search for the isolation of bridging bis‐borylene species of Rh, we have treated [Co₂(CO)₈] with nido‐[(RhCp*)₂(B₃H₇)], which afforded triply‐bridging bis‐borylene species [(μ₃‐BH)₂(RhCp*)₂Co₂(CO)₄(μ‐CO)] ( 3 ). All the compounds have been characterized by means of single‐crystal X‐ray diffraction study; ¹H, ¹¹B, ¹³C NMR spectroscopy; IR spectroscopy and mass spectrometry.     

Study of the Suppression of Porphyrin Emission upon Addition of Rare Earth Ions

A topic of constant investigation in recent decades has been the study of electron and/or energy transfer reactions in supramolecular systems. The energy transfer between donor-acceptor depends on the influence of the substituent in the intersystem crossing. The competition between the radiative and non-radiative processes also depends on other factors such as temperature, solvent and energy gap. In this work, we have studied the suppression of the emission of monocarboxyphenyl porphyrins after addition of rare earth ions (RE(III)). The porphyrin emission decreases with the addition of RE(III), no matter which ion is present. When Eu(III) was used, the emission of this ion was not observed either. This suppression happens due to the effect of the heavy atom and not due to the energy transfer through electronic levels between the porphyrin and the RE(III). After the addition of RE(III), the lifetime for MCTPPH₂ started to decay biexponentially, indicating the formation of a new species (MCTPPH₂-RE(III)) of a shorter lifetime. The presence of NO₂ groups in the ortho mesoaryl positions of MCTNPPH₂ and the presence of Zn(II) in Zn(MCTPP) decreased both the porphyrin lifetime and emission due to an increase in the spin-orbit coupling.     

NMR parameters of the tetrahedrane [Fe2(CO)6(μ-SNH)], studied by experiment and DFT

The intramolecular dynamic behavior of the tetrahedrane-type cluster [Fe₂(CO)₆(μ-SNH)] 1 was studied by ¹³C NMR spectroscopy. The ⁵⁷Fe chemical shift of 1 and the coupling constants ¹ J(⁵⁷Fe,¹³C) were measured. These NMR parameters, and also ¹ J(⁵⁷Fe,¹⁵N), were found to be in good agreement with data calculated by using density functional theory (DFT) methods (B3LYP), based on the geometry calculated at the 6-311+G(d,p) level of theory. The isolobal replacement of the Fe(CO)₃ with BH fragments leads to the tetrahedranes [Fe(CO)₃(BH)(μ-SNH)] 2 and [(HB)₂(μ-SNH)] 3. Both were identified by calculations as minima on the respective potential energy surface (PES). However, the tetrahedrane-type structure of 3 is much higher in energy when compared with the planar cyclic isomers 3a and 3b.     

Pyrromethene–BF2 complexes as laser dyes: 2

Pyrromethene–BF₂ complexes (P–BF₂) 7 were obtained from α-unsubstituted pyrroles 5 by acylation and condensation to give intermediate pyrromethene hydrohalides 6 followed by treatment with boron trifluoride etherate. Conversion of ethyl α-pyrrolecarboxylates 4 to α-unsubstituted pyrroles 5 was brought about by thermolysis in phosphoric acid at 160°C, or by saponification followed by decarboxylation in ethanolamine at 180°C, or as unisolated intermediates in the conversion of esters 4 to pyrromethene hydrobromides 6 by heating in a mixture of formic and hydrobromic acids. Addition of hydrogen cyanide followed by dehydrogenation by treatment with bromine converted 3,5,3′,5′-tetramethyl-4,4′-diethylpyrromethene hydrobromide 9 to 3,5,-3′,5′-tetramethyl-4,4′-diethyl-6-cyanopyrromethene hydrobromide 6bb , confirmed by the further conversion to 1,3,5,7-tetramethyl-2,6-diethyl-8-cyanopyrromethene–BF₂ complex 7bb on treatment with boron trifluoride etherate. An alternation effect in the relative efficiency (RE) of laser activity in 1,3,5,7,8-pentamethyl-2,6-di-n-alkylpyrromethene–BF₂ dyes depended on the number of methylene units in the n-alkyl substituent, -(CH₂)_nH, to give RE ≥ 100 when n = 0,2,4 and RE 65, 85 when n = 1,3. (The RE 100 was arbitrarily assigned to the dye rhodamine 6G). The absence of fluorescence and laser activity in 1,3,5,7-tetramethyl-2,6-diethyl-8-isopropylpyrromethene–BF₂ complex 7p and a markedly diminished fluorescence quantum yield (Φ 0.23) and lack of laser activity in 1,3,5,7-tetramethyl-2,6-diethyl-8-cyclohexylpyrromethene–BF₂ complex 7q were attributed to molecular nonplanarity brought about by the steric interference between each of the two bulky 8-substituents with the 1,7-dimethyl substituents. An atypically low RE 20 for a peralkylated dye without steric interference was observed for 1,2,6,7-bistrimethylene-3,5,8-trimethylpyrromethene–BF₂ complex 7j . Comparisons with peralkylated dyes revealed a major reduction in RE 0–40 for the six dyes 7u–z lacking substitution at the 8-position. Low laser activity RE was brought about by functional group (polar) substitution in the 2,6-diphenyl derivative 7I , RE 20, and the 2,6-diacetamido derivative 7m , RE 5, of 1,3,5,7,8-pentamethylpyrromethene–BF₂ complex (PMP–BF₂) 7a and in 1,7-dimethoxy-2,3,5,6,8-pentamethylpyrromethene–BF₂ complex 7n , RE 30. Diethyl 1,3,5,7-tetramethyl-8-cyanopyrromethene-2,6-dicarboxylate–BF₂ complex, 7aa , and 1,3,5,7-tetramethyl-2,6-diethyl-8-cyanopyrromethene–BF₂ complex, 7bb , offered examples of P–BF₂ dyes with electron withdrawing substituents at the 8-position. The dye 7aa , λ_las 617 nm, showed nearly twice the power efficiency that was obtained from rhodamine B, λ_las 611 nm.     

Reinvestigation of intramolecular hydrogen bond in malonaldehyde derivatives: An ab initio,AIM and NBO study

The RAHB systems in malonaldehyde and its derivatives at MP2/ 6‐311++G(d,p) level of theory were studied and their intramolecular hydrogen bond energies by using the related rotamers method was obtained. The topological properties of electron density distribution in O? H···O intramolecular hydrogen bond have been analyzed in term of quantum theory of atoms in molecules (QTAIM). Correlations between the H‐bond strength and topological parameters are probed. The results of QTAIM clearly showed that the linear correlation between the electron density distribution at HB critical point and RAHB ring critical point with the corresponding hydrogen bond energies was obtained. Moreover, it was found a linear correlation between the electronic potential energy density, V(r_cp), and hydrogen bond energy which can be used as a simple equation for evaluation of HB energy in complex RAHB systems. Finally, the similar linear treatment between the geometrical parameters, such as O···O or O? H distance, and Lp(O)→σ*_OH charge transfer energy with the intramolecular hydrogen bond energy is observed. © 2010 Wiley Periodicals, Inc., Int J Quantum Chem, 2011     

Synthesis of carboxymethyl potato starch and comparison of optimal reaction conditions from different sources

Carboxymethyl potato starch (CMPS) was synthesized under heterogeneous reaction conditions. The influences of etherification temperature, alkalization and etherification time, sodium hydroxide to monochloroacetic acid (MCA) molar ratio (n_NaOH/n_MCA), theoretical degree of substitution (DS_t), the ratio of isopropyl alcohol (IPA) volume to starch mass (v_IPA/m_st) on degree of substitution (DS) and reaction efficiency (RE) of CMPS were investigated. Compared with the previous literature data, the results had significant difference for the optimal carboxymethylation conditions of potato starch from different sources. CMPS prepared under optimal conditions showed the highest DS and RE, which were 1.36 and 0.88, respectively. Furthermore, the RE value in this work is considerably higher than that reported in the literature. The time of alkalization and etherification were also discussed independently. In addition, CMPS was characterized by Fourier transform infrared spectrophotometry and scanning electron microscopy (SEM). Copyright © 2008 John Wiley & Sons, Ltd.