Planar D3h Research Articles

Molecular structures and energies of low-lying [formula omitted] clusters: Comparison with [formula omitted] clusters

The structures and energies of LixSix(x=1–4) were investigated by the DFT and MP2 methods by using a variety of basis sets of 6-31G(d), 6-311+G(2df), and cc-pVXZ (X=T, Q, 5). Two singlet low-lying doubly-bridged bent (C2v) and planar (D2h) structures are found to be the global minimum and a transition state on the potential energy surface of Li2Si2, respectively. The preference of polylithium compounds LixSix(x=2–4) for nonclassical structures can be taken as an indication that the extensive bonding prevails presumably owing to ionic contribution.

Raman and infrared spectral studies of [C(NH2)3]2MII(H2O)4(SO4)2, MII = Mn, Cd and VO

AbstractThe Raman and FTIR spectra of three metal guanidinium sulfates, [C(NH2)3]2MII(H2O)4(SO4)2, (MII = Mn, Cd and VO), are recorded. The observed spectral bands are assigned in terms of the fundamental modes of vibration of the guanidinium ions, sulfate groups and water molecules. The appearance of the sulfate tetrahedra's ν1 and ν2 modes in the IR spectra and the partial lifting of the ν4 mode in the Raman spectra indicate the distortion of the SO42− tetrahedra in the structure, so that its symmetry is lowered from Td to C1. The geometry of the sulfate group in guanidinium vanadyl sulfate does not deviate much from that of the average sulfate group. The distortion of the SO4 tetrahedra is stronger in GuCds than in GuMnS. The CN3 group in the guanidinium ion is planar (D3h point group) in GuCdS and GuMnS, whereas it is lowered in the vanadyl compound. Furthermore, the spectral analyses show the presence of weak hydrogen bonds in the structures. Copyright © 2007 John Wiley & Sons, Ltd.

High-Accuracy Structure of Cyclobutane by Femtosecond Rotational Raman Four-Wave Mixing

The femtosecond degenerate four-wave mixing (fs-DFWM) technique is applied for the measurement of accurate rotational constants of cyclobutane (C4H8). The vibrational levels of C4H8 exhibit tunneling splitting due to the ring-puckering interconversion between the symmetry-equivalent D2d minima via a planar D4h barrier. For the v = 0 ground state, the fs-DFWM method yields a rotational constant B + 0 = 10663.452(18) MHz. The ring-puckering tunneling leads to slightly different rotational constants for the 0+ and 0- levels, B + 0 - B -0 = 33 +/- 2 kHz. This difference increases by a factor of approximately 90 in the v = 1+/1- ring-puckering states to B +1 - B -1 = -3059 +/- 4 kHz. Combining the experimental rotational constants with the structure parameters and rotational constants calculated by high-level ab initio calculations allows us to determine accurate equilibrium and vibrationally averaged structure parameters for cyclobutane, for example, re(C-C) = 1.5474 A, re(C-Haxial) = 1.0830 A, re(C-Hequatorial) = 1.0810 A, and ring puckering angle theta e = 29.8 degrees .

Matrix Isolation Infrared Spectroscopic and Theoretical Study of Dinuclear Chromium Oxide Clusters: Cr2On (n = 2, 4, 6) in Solid Argon

Dichromium oxide clusters, Cr2O2, Cr2O4, and Cr2O6, have been prepared and characterized by matrix isolation infrared spectroscopy and quantum chemical calculations. Laser-evaporated chromium atoms reacted with O2 in solid argon to form the previously characterized CrO2 molecules, which further reacted with chromium atoms to form Cr2O2 spontaneously on annealing. The Cr2O2 cluster is determined to have a chainlike CrOCrO structure. The rhombic ring isomer, which was predicted to be more stable than the CrOCrO structure, was not formed at the present experimental conditions. The Cr2O4 cluster was formed from the barrierless dimerization of the chromium dioxide molecules, which is characterized to have a planar D2h symmetry. TheCr2O6 cluster was produced under UV light irradiation. It is determined to have a singlet ground state with a nonplanar D2h symmetry.

Identification of the Radical Anions of C2N4S2and P2N4S2Rings by In Situ EPR Spectroelectrochemistry and DFT Calculations

The previously unknown radical anions of unsaturated E2N4S2 ring systems (E=RC, R2NC, R2P) can be generated voltammetrically by the one-electron reduction of the neutral species and, despite half-lives on the order of a few seconds, have been unambiguously characterized by electron paramagnetic resonance (EPR) spectroelectrochemistry using a highly sensitive in situ electrolysis cell. Cyclic voltammetric studies using a glassy-carbon working electrode in CH3CN and CH2Cl2 with [nBu4N][PF6] as the supporting electrolyte gave reversible formal potentials for the [E2N4S2]0/- process in the range of -1.25 to -1.77 V and irreversible peak potentials for oxidation in the range of 0.66 to 1.60 V (vs the Fc+/0 couple; Fc=ferrocene). Reduction of the neutral compound undergoes an electrochemically reversible one-electron transfer, followed by the decay of the anion to an unknown species via a first-order (chemical) reaction pathway. The values of the first-order rate constant, kf, for the decay of all the radical anions in CH2Cl2 have been estimated from the decay of the EPR signals for (X-C6H4CN2S)2*-, where X=4-OCH3 (kf=0.04 s(-1)), 4-CH3 (kf=0.02 s(-1)), 4-H (kf=0.08 s(-1)), 4-Cl (kf=0.05 s(-1)), 4-CF3 (kf=0.05 s(-1)), or 3-CF3 (kf=0.07 s(-1)), and for [(CH3)3CCN2S]2*- (kf=0.02 s(-1)), [(CH3)2NCN2S]2*- (kf=0.05 s(-1)), and [(C6H5)2PN2S]2*- (kf=0.7 s(-1)). Values of kf for X=4-H and for [(CH3)2NCN2S]2*- were also determined from the cyclic voltammetric responses (in CH2Cl2) and were both found to be 0.05 s(-1). Possible pathways for the first-order anion decomposition that are consistent with the experimental observations are discussed. Density functional theory calculations at the UB3LYP/6-31G(d) level of theory predict the structures of the radical anions as either planar (D2h) or folded (C2v) species; the calculated hyperfine coupling constants are in excellent agreement with experimental results. Linear correlations were observed between the voltammetrically determined potentials and both the orbital energies and Hammett coefficients for the neutral aryl-substituted rings.

δ Aromaticity in [Ta3O3]−

We report experimental and theoretical evidence of -aromaticity, which is discovered in the Ta3O3 – cluster via a combined photoelectron spectroscopy and ab initio study. Well-resolved low-lying electronic transitions are observed in the photoelectron spectra of Ta3O3 – and are compared with ab initio calculations, which show that the Ta3O3 – cluster possesses a planar D3h triangular structure. Chemical bonding analyses reveal that among the five valence molecular orbitals responsible for the multi-center metal-metal bonding there is a completely bonding delta and orbital from the 5d atomic orbitals of Ta. The totally delocalized multi-center bond renders -aromaticity for Ta3O3 – and represents a new mode of chemical bonding. Ta3O3 – is the first -aromatic molecule confirmed experimentally and theoretically, suggesting that -aromaticity may exist in many multi-nuclear, low oxidation state transition-metal compounds.

A quantum chemistry study: A new kind of boron nitrides

At the B3LYP/6-311+G** and the BP86/6-311+G** levels of theory, BNN, H(3)BNN, NNBH(2)-BH(2)NN, (BNN)(2)H(2), NNBBNN, (BNN)(3) (+), (BNN)(4), (BNN)(4) (2+), (BNN)(4) (2-), B(4)(NN)(2), (BNN)(5) (-), (BNN)(6), (BNN)(7) (+), and (BNN)(8) (2+) are investigated. Neutral (BNN)(4) is aromatic with its triplet state but antiaromatic with its singlet state. (BNN)(4) dication favors D(2d) structure, while (BNN)(4) dianion favors a planar D(4h) structure. (BNN)(3) (+), (BNN)(4) (2-), (BNN)(5) (-), (BNN)(6), (BNN)(7) (+), (BNN)(7) (3-), (BNN)(8) (2+), and (BNN)(8) (2-) are all aromatic with planar monocyclic conformation, following the 4n + 2 rule. Moreover, according to the CASSCF and MRCI calculations, the planar B(4)(NN)(2) of D(2h) symmetry prefers to be a sigma-pi diradical in spite of open-shell singlet or triplet and is also aromatic. Akin to the sigma-pi back interaction in compounds containing transition metal, there exists the sigma-pi back interaction between boron and N(2) ligand among some species reported herein, which strengthens B(-)N bond but activates N-N bond, especially in (4)Sigma(-) BNN. The T-shaped structure lies lowest in energy among seven isomers of the (BNN)(2)H(2) dimer, and the parallel-displaced structure is favored between two isomers of the (BNN)(6) dimer.

Spatial Structure of Au8: Importance of Basis Set Completeness and Geometry Relaxation

The relative stabilities of the lowest energy structures are calculated for the gold octamer, Au8, employing highly correlated ab initio methods. The question of dimensionality of these clusters is addressed, and a guideline for future structural studies of such systems is provided. In particular, the importance of geometry relaxation beyond the MP2 level of theory as well as the need for basis sets toward the complete limit (CBS) are discussed. The planar D(4h) symmetric structure of Au8 is the lowest energy structure. At the CCSD(T)/CBS limit, it is separated by 16 kJ mol(-1) from the next higher Td symmetric isomer.

Electron−Phonon Interactions and Jahn−Teller Effects in the Monocation of Corannulene

Electron-phonon interactions in the monocation of corannulene are studied by using the hybrid Hartree-Fock (HF)/density-functional-theory (DFT) method in the Gaussian 98 program package. The C-C stretching mode of 1498 cm(-1) most strongly couples to the e1 highest occupied molecular orbitals (HOMO) in corannulene. The total electron-phonon coupling constant for the monocation (l(HOMO)) of corannulene is estimated to be 0.165 eV. The l(HOMO) value for corannulene is much larger than those for coronene and acenes with similar numbers of carbon atoms. The delocalized electronic structures and the intermediate characteristics between the strong sigma-orbital interactions and weak pi-orbital interactions originating from a bowl-shaped C(5v) geometry are the main reason that the l(HOMO) value for corannulene is much larger than those for planar D(6h) symmetric pi-conjugated coronene and D(2h) symmetric pi-conjugated acenes with similar numbers of carbon atoms. The electron transfer in the positively charged corannulene is also discussed. Intramolecular electron mobility (sigma(intra,monocation)) in the positively charged corannulene is estimated to be smaller than those for the positively charged pi-conjugated acenes and coronene. The reorganization energy for the positively charged corannulene (0.060 eV) is estimated to be larger than those for the positively charged acenes and coronene. The strong orbital interactions between two neighboring carbon atoms in the HOMO of corannulene with the bowl-shaped structure are the main reasons for the calculated results. Thus, the larger overlap integral between two neighboring molecules is needed for the positively charged corannulene to become a better conductor than those for positively charged coronene and acenes. The smaller density of states at the Fermi level n(0) values are enough for the conditions of the attractive electron-electron interactions to be realized in the monocation of corannulene than in the monocations of coronene and acenes with similar numbers of carbon atoms. The multimode problem is also treated in order to investigate how consideration of the multimode problem is closely related to the characteristics of the electron-phonon interactions.

Theoretical Study on the Small Clusters of LiH, NaH, BeH2, and MgH2

High-level ab initio molecular orbital theory is used to calculate the geometries, vibrational frequencies, atomic charges, and binding energies of the small clusters (LiH)(n), (NaH)(n), (BeH(2))(n), and (MgH(2))(n) (n = 1-4). For (LiH)(n) and (NaH)(n), there are planar cyclic structures when n = 2, 3. We have found the cubic structure T(d) in addition to the planar cyclic D(4)(h) when n = 4. The D(4)(h) is less stable than the T(d) geometry. For (BeH(2))(n) and (MgH(2))(n), when n = 3, there are three kinds of structures: chain C(2)(v), planar cyclic D(3)(h), and hat-like C(2)(v). The C(2)(v) geometry is more stable than the others. When n = 4, there are four kinds of structures: chain D(2)(h), cubic T(d), string-like C(2), and cubic transformation C(1). The most stable compounds in the families of (LiH)(n), (NaH)(n), (BeH(2))(n), and (MgH(2))(n) are cubic T(d), cubic T(d), chain D(2)(h), and string-like C(2) geometries, respectively, when n = 4. Calculated binding energies range from -24 to -37 kcal/mol for (LiH)(n) and --19 to -30 kcal/mol for (NaH)(n), (BeH(2))(n), and (MgH(2))(n). The hydrogen atoms in hydride clusters always have negative charges. The atomic charges of planar cyclic structures are weaker than those of cubic structures, and there is a tendency of reducing along with the increase of the cluster size. The vibrational frequencies of planar cyclic structures have consistent tendency, too. It indicates that the bond distance increases with the ionic character of the bond.

Theoretical Studies of Inorganic Compounds. 341) Energy Decomposition Analysis of E–E Bonding in Planar and Perpendicular X2E−EX2 (E = B, Al, Ga, In, Tl; X = H, F, Cl, Br, I)

AbstractThe nature of E–E bonding in group 13 compounds X2E–EX2 (E = B, Al, Ga, In, Tl; X = H, F, Cl, Br, I) has been investigated by means of an energy decomposition analysis (EDA) at the BP86/TZ2P level of theory. The calculated equilibrium geometries of all molecules B2X4−Tl2X4 have a perpendicular (D2d) geometry. The largest energy barriers for rotation about the E‐E bond are predicted for the hydrogen species B2H4−Tl2H4. The EDA shows that the rotational barriers of B2X4−Tl2X4 may not be used for an estimate of the hyperconjugative strength in the D2d structures except for the tetrahydrides. The values for the planar (D2h) transition states reveals that π conjugation of the halogen lone‐pair electrons stabilizes the transition states. The bonding analysis shows that hyperconjugation in B2I4 is stronger than in B2H4 although the latter compound has a higher rotational barrier than the former. In B2F4, hyperconjugative stabilization of the perpendicular structure and conjugative stabilization of the planar structure nearly cancel each other yielding a nearly vanishing rotational barrier. The heavier analogues Al2X4−Tl2X4 have low rotational barriers and rather weak hyperconjugative interactions. The larger rotational barriers of the hydrogen systems Al2H4−Tl2H4 compared with the tetrahalogen compounds is explained with the cooperation of the relatively large hyperconjugation in the perpendicular form and the relatively weak conjugation in the planar transition structures. The EDA also indicates that the electrostatic (ΔEelstat) and molecular orbital (ΔEorb) components of the E–E bonding are similar in magnitude.Thecalculated B‐B bond dissociation energies of B2X4 (De = 93.0–108.4 kcal/mol) show that the bonds are rather strong. The heavier analogues Al2X4−Tl2X4 have weaker bonds (De = 16.6–61.7 kcal/mol). In general, the X2E‐EX2 bond dissociation energies follow the trend for atoms E: B ≫ Al > Ga > In > Tl and for atoms X: H > F > Cl > I.

Dicyclobuta[de,ij]naphthalene and Dicyclopenta[cd,gh]pentalene: A Theoretical Study

The structures, energetics, and aromatic character of dicyclobuta[de,ij]naphthalene, 1, dicyclopenta[cd,gh]pentalene, 2, dihydrodicyclobuta[de,ij]naphthalene, 3, and dihydrocyclopenta[cd,gh]pentalene, 4, have been examined at the B3LYP/6-311++G//B3LYP/6-31G level of theory. All molecules are bowl-shaped, and the pentalene isomers, 2 and 4, are most stable. A comparison with other C(12)H(6) and C(12)H(8) isomers indicates that 2 is approximately 25 kcal/mol less stable than 1,5,9-tridehydro[12]annulene and 4 is approximately 100 kcal/mol higher in energy than acenaphthylene, both of which are synthetically accessible. The transition state structure for bowl-to-bowl inversion of 1 is planar (D(2)(h)()) and lies 30.9 kcal/mol higher in energy than the ground state; the transition state for inversion of 2 is C(2)(h)() and lies 46.6 kcal/mol higher in energy. Symmetry considerations, bond length alternations, and NICS values (a magnetic criterion) all indicate that the ground states of 1, 3, and 4 are very aromatic; however, HOMA values (a measure of bond delocalization) indicate that 3S and 4S are aromatic but that 1S is less so. NICS values for the ground state of 2 strongly indicate aromaticity; however, bond localization, symmetry, and HOMA values argue otherwise.

Density functional theory studies of lithium porphyrin radicals

The ground-state geometries of monolithium porphyrin (LiP) π-radical and its three reduced/oxidized species ([LiP]−, [LiP]2−, and [LiP]+) have been calculated with the density functional theory. The results show that LiP, [LiP]− and [LiP]+ have planar D4h structures while the [LiP]2− dianion has a rectangular distorted D2h structure due to the ground-state Jahn-Teller effect. LiTPP and LiOEP radicals were also studied to assess the effect of peripheral substitutions. The ground-state LiTPP has a normal porphyrin ring (D4h effective symmetry), while the ground-state LiOEP has a porphyrin ring with pronounced bond length alternation (C4h effective symmetry) due to the pseudo-Jahn-Teller (pJT) distortion along an A2g-like coordinate. The spin densities of LiP, LiTPP, and LiOEP were analyzed, showing evident effects of peripheral substitution. Electronic absorption spectrum of LiP radical was calculated with the time-dependent DFT and was compared with the experimental results of LiTPP.

Ab initio structural study of M(mda)2 complexes (M = Be, Mg, Ca; mda = C3O2H3)

The structure of M(mda)2 (M = Be, Mg, Ca; mda = C3O2H3) bis-complexes was investigated by the ab initio Hartree-Fock method and by including electron correlation in terms of second order Moller-Plesset perturbation theory; for calculations we used triple-zeta valence basis sets complemented with polarization functions. Two most probable geometrical nuclear configurations (D2h and D2d) are considered for each molecule. The structure with two mutually orthogonal chelate ligands (D2d symmetry) corresponds to the potential energy surface (PES) minimum. The planar D2h configuration corresponds to the first order saddle point on PES; consequently, its relative energy determines the height of the barrier to the D2d→D2h→D2d′ intramolecular rearrangement. Correlation equations that relate the calculated values of equilibrium internuclear distances, force constants, and rearrangement barrier heights to the value of the ionic radius of the metal atom have been obtained. These correlations were employed to evaluate the molecular constants for Sr(mda)2 and Ba(mda)2. The theoretical data are compared with the available experimental literature data.

A computational study of the electron detachment energies of Al2As2 − and Al3As3 −

Ab initio and density functional theory calculations are reported for the low-lying electronic states of Al2As2 −, Al2As2, Al3As3 −, and Al3As3. The 2B2g ground electronic state of Al2As2 − has a rhombic structure with the Al atoms occupying the shorter diagonal. In contrast, the As atoms occupy the shorter diagonal of the ground state rhombic structure of Al2As2. Electron detachment energies computed for Al2As2 − are presented and discussed. The adiabatic electron affinity of Al2As2 − is calculated to be 2.1 eV at the CCSD(T) level, using B3LYP and MP2 optimized geometries. The ground states of both Al3As3 − (2A1′) and Al3As3 (1A1′) have planar hexagonal D3h geometry. Electron detachment energies computed for the anion are reported. At the CCSD(T)//B3LYP level, the electron affinity of Al3As3 is calculated to be 2.47 eV.

Structure and Bonding in B6‐ and B6: Planarity and Antiaromaticity.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Pseudo-Jahn−Teller Distortion from Planarity in Heterocyclic Seven- and Eight-Membered Ring Systems with Eight π Electrons

To elucidate the nature of a pseudo-Jahn−Teller (JT) distortion from planarity, ab initio MCSCF calculations with the 6-31G(d,p) basis sets were carried out in the ground states of seven- and eight-membered unsaturated heterocycles with eight π electrons. The monocyclic systems examined were found to show a variety of structural changes. Azepine and oxepin undergo the pseudo-JT distortions from a planar C2v to a boat Cs conformation. In 1,5-diazocine, the pseudo-JT distortion takes place in two stages, the initial step being from a symmetric planar D2h to a skew C2h structure and the subsequent step from the skew C2h to a tub C2 structure. The 1,3,5,7-tetrazocine molecule undergoes pseudo-JT distortions from a symmetric planar D4h to skew C4h and crown-like D2d structures through the respective in-plane and out-of-plane nuclear deformations. Moreover, the C4h and D2d structures are distorted into the same tub-shaped S4 conformation. An inspection of the energy components comprised in the total energy reveals that the stability of nonplanar structures arises from a lowering of the electron−nuclear attraction energy. The energy variation is accounted for in terms of an electrostatic interaction and the proximity among the nuclei and electron clouds owing to a folding of the molecular skeleton. It is shown that the theoretical structural characteristics for azepine, oxepin, 1,5-diazocine, and 1,3,5,7-tetrazocine are in good agreement with available experimental facts.

Molecular Geometry of Monomeric and Dimeric Yttrium Trichloride from Gas-Phase Electron Diffraction and Quantum Chemical Calculations

The molecular geometry of yttrium trichloride has been determined by high-temperature gas-phase electron diffraction. The vapor phase consisted of about 87% monomeric and 13% dimeric species. High-level quantum chemical calculations have also been carried out for both the monomer and dimer of yttrium trichloride, and their geometries, harmonic force fields, and vibrational frequencies have been determined. The monomer YCl3 molecule was found to be planar (D3h symmetry) both by experiment and by computation. The bond length of YCl3 from electron diffraction is 2.450(7) (rg) or 2.422(12) (re) Å. It proved remarkably difficult to obtain a converged theoretical prediction for the bond length; large polarization bases are needed, and the published bases accompanying the pseudopotentials used appear to be overcontracted. The SCF method predicts bonds that are too long by some 0.043 Å, whereas the B3LYP method overestimates by about 0.03 Å. The B3PW91 prediction is almost within the experimental uncertainty for re. Among the traditional correlated methods, the MP2 distance with an infinitely large basis is probably indistinguishable from the experimental value, given the combined uncertainties, whereas the estimated CCSD(T) result of 2.423(10) Å is astonishingly close to the experimental result. The out-of-plane bending motion for YCl3 is noticeably anharmonic, with the result that straightforward quantum predictions of its frequency are lower than the value observed in the gas phase at high temperature.

Structure and Bonding in B6- and B6: Planarity and Antiaromaticity

The electronic structure and chemical bonding of B6- and B6 were investigated using anion photoelectron spectroscopy and ab initio calculation. Vibrationally resolved photoelectron spectra were obtained for B6- and were compared to calculations performed at various levels of theory. Extensive searches were carried out for the global minimum of B6-, which was found to have a planar D2h structure with a doublet ground state (2B2g). Good agreement was observed between ab initio detachment energies and the experimental spectra, establishing that the ground-state structure of B6- is planar, in contrast to the three-dimensional structures for the valence-isoelectronic Al6- and Al6 species. The chemical bonding in B6- was interpreted in terms of linear combinations of molecular orbitals of two B3- fragments. The antiaromatic nature of chemical bonding was established for B6- and B62-, based on the analysis of orbital contributions to overall paratropic ring currents.

Frontier orbital and density functional study of the variation of the hard–soft behavior of monoborane (BH3) and boron trifluoride (BF3) as a function of angles of reorganization from planar (D3h) to pyramidal (C3v) shape

AbstractIn chemical response the BH3 and BF3 molecules undergo the physical process of planar (D3h) to pyramidal (C3v) reorganization in shape as the condition precedent to the event of chemical reaction under the requirement of symmetry. A frontier orbital and density functional study of the variation of the stability of electronic structures and chemical reactivity of associated with the physical process of D3h to C3v geometry reorganization has been performed. The theoretical parameters viz. eigenvalues of HOMO and LUMO, the HOMO and LUMO energy gap, the global hardness and global softness, the chemical potential, the condensed Fukui function, and local softness of B atom, the reaction site, have been computed over a wide range of ∠XBX angles. The nature of variation in the intrinsic chemical reactivity, global and local, of the molecules associated with their geometry reorganization during the chemical event of charge transfer interaction involving their frontier molecular orbitals has been quantitatively explored. The hardness profiles as a function of reaction coordinates are consistent with the principle of maximum hardness (PMH). Results demonstrate that the hardness and softness are not a static and invariable property of molecules but a dynamic and variable function of molecular structure. The hardness parameters and the HOMO–LUMO gap of the molecules are so modified with the distortion of molecular geometry that, after a certain stage of molecular deformation, the profiles of such parameters of the molecules intersect and cross each other, signifying that the relative order of the intrinsic hardness of their equilibrium geometry is reversed. The intrinsically hard molecule BF3 becomes softer than the intrinsically soft molecule BH3 as a consequence of structural distortion. The increase in chemical reactivity computed in terms of density functional parameters are transparent and justified in terms of the profiles of the eigenvalues of the frontier orbitals. The profiles of chemical potential reveal the inherent difference in the tendency of backdonation from two molecules. The computed values of Fukui functions and local softness parameters of the B atom site demonstrate that the concept of local softness can be exploited for a theoretical analysis and understanding of the characteristic chemical events of the molecules under consideration. The profiles of the Fukui functions and local softness parameters of the two molecules seem to reflect and reveal their intrinsic difference in the tendency of receiving donation in the LUMO (electrophilicity) and that of backdonation from the HOMO (nucleophilicity) and the inherent difference of overall reactivity of the two molecules by a simultaneous operation of two opposing processes of charge transfer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003