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Huang X.,South China Normal University | Tan Y.,South China Normal University | Xu X.,South China Normal University | Xu X.,Key Laboratory of Theoretical Chemistry of Environment | And 3 more authors.
Acta Chimica Sinica | Year: 2012

The geometrical and electronic structures of heterometal string complexes [CuCuM (npa)4Cl]+ (1:M=Pt, 2:M= Pd, 3: M=Ni) were investigated theoretically by density functional theory UBP86 method with incorporating the external electric field along the metal chain in Cl→M(r) and M(r)→Cl two directions. In general, under the electric field, the spin densities of the high potential end decrease while that of the low potential end increase, and the negative charge transfers to the high potential end. When the electric field enhances, the molecular energy decreases and the dipole moment increases linearly. With the increase of the electric field, the spatial distribution of frontier orbitals changes regularly, and the energies of frontier occupied orbitals increase in the sensitive order of πnb > σ* > δM(r)-N(r) *, which leads to the frontier occupied orbital level crossing. When the Cl→M(r) electric field is applied, the spin densities delocalize from Cu to M(r), and the positive charge transfers from Cu to M(r). Moreover, the molecular energy decreases more sensitively. Also in the Cl→M(r) electric field, the contractions of Cu-Cu and Cu-M(r) distances and the decrease of the frontier orbital energy gap are beneficial to the electron transport of the metal string complexes. However, under the M(r)→Cl electric field, the distances of Cu-Cu and Cu-M increase. The effect of M(r)→Cl electric field on the molecular energy, spin density and charge density of metal atoms are less obvious than that of Cl→M(r) electric field. When the electric field increases to some extent, the spin densities of the metal atoms remain stable values, and the changes of them are obviously asymmetric in Cl→M(r) and M(r)→Cl directions. Therefore, 1~3 may have the potential application of molecular rectifier. © 2012 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. Source

Ding D.-D.,South China Normal University | Xu X.,South China Normal University | Xu X.,Key Laboratory of Theoretical Chemistry of Environment | Xu X.,Key Laboratory of ElectroChemical Technology on Energy Storage and Power Generation in Guangdong Universities | And 7 more authors.
Wuli Huaxue Xuebao/ Acta Physico - Chimica Sinica | Year: 2015

The coordination structures of metal string complexes (n, m)[Cr3(PhPyF)4Cl2] (HPhPyF=N,N'-phenylpyridylformamidine; n=2, 3, 4; m=2, 1, 0) with potential applications as molecular wires have been investigated using the density functional theory BP86 method by considering the effects of an external electric field (EF). Herein, n and m represent the number of benzene rings on the left and right in the PhPyF- ligand, respectively. The results show that: (1) under zero field, the three kinds of coordination modes ((2, 2), (3, 1), (4, 0)) of the four PhPyF- ligands are close in energy, which indicates that they are competitive conformations. The (2, 2) coordination mode is the most stable one. The Cl axial ligands on the two sides of (4, 0) can coordinate to Cr atoms, indicating that these two axial ligands can combine with electrodes. Moreover, the Cl4―Cr1 bond is stronger than Cl5―Cr3, different from (4, 0) [CuCuM(npa)4Cl] [PF6] (M=Pd, Pt; 2-naphthyridylphenylamine) in which the axial ligand Cl close to benzene cannot coordinate to metal atom M. (2) There is a 3-center-3-electron delocalization σ bond in the Cr36+ chain for (2, 2), (3, 1), and (4, 0), but the delocalization gradually weakens. The polarity from Cl4 to Cl5 is stronger as the coordination mode of four PhPyF- ligands becomes more consistent. (3) The geometry and electronic structure of the investigated complexes change regularly under the electric field. Because the electron transfer direction of (3, 1) and (4, 0) is the same as its molecular polarity, the bond length, spin density, charge and energy gap are more sensitive to -Z electric field. Therefore, the -Z elelctric field is beneficial to the conductivity of the molecules. Moreover, the sensitivity of the structures to electric field increases with polarity. © 2015 Editorial office of Acta Physico-Chimica Sinica. Source

Zhou W.,South China Normal University | Chen R.,South China Normal University | Wu Z.,South China Normal University | Ding D.,South China Normal University | And 7 more authors.
Acta Chimica Sinica | Year: 2015

The asymmetric heterometal string complexes [Cu2Pt(npa)4X2] (X=Cl-(1), NCS-(2), npa=2-naphthyridyl- phenylamine) are suitable candidates for promising inorganic molecule rectifiers. The electronic structures and transmission properties of them were investigated by theoretical calculation using Density Function Theory BP86 and Non Equilibrium Green's Functions method. The results revealed that: (1) Since the interaction between axial ligand NCS- and Cu atom is stronger than that of Cl-Cu, the Cu-Cu bond of complex 1 is stronger than that in 2, while its Cu-Pt bond is weaker than that in 2. Therefore, complex 1 has smaller energy gap ΔE between π* Pt dxz/yz and π* Cu-Cu orbital compared with that of 2. (2) The transmission channels of 1 and 2 both are β spin π* orbitals, which are mainly combination of π* Cu-Cu and π* Pt dxz/yz orbital. The smaller ΔE, the larger delocalization of π* channel, and hence the stronger transmission capacity. When the positive bias is less than 0.15 V and under negative bias, current of 1 is greater than that of 2 for the smaller ΔE of 1. However when the positive bias is larger than 0.15 V, current of 2 is significantly higher than that of 1 for the stronger delocalization of π* channel in 2. (3) The complex 2 has better rectifying effect. With a larger ΔE, the transmission of Pt → Cu direction is easier and the rectifying effect is stronger. Current of 2 under the positive bias is significantly greater than that in negative bias. When the bias is larger than 0.15 V, the rectified ratio of 2 is 10~40 times larger than 1. (4) With the ΔEβ smaller than ΔEα, the transmission capacity of α spin channel is less than β, and the effect of the spin filter will be stronger for the larger difference between ΔEβ and ΔEα. Both 1 and 2 have significant spin filter effect (up to 80%~99%). © 2015 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. Source

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