The Intramolecular Spin-Spin Interactions in Ruthenium Complexes of Pyrazole Derivatives

Peter A. Ajibade

Department of Chemistry, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa

The Intramolecular Spin-Spin Interactions in Ruthenium Complexes of Pyrazole Derivatives

Peter A. Ajibade

Department of Chemistry, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa

The spin-spin coupling can provide useful information for analysing the structure of a system and the extent of non-covalent bonds interactions. In this study, we present the isotropic NMR properties and spin-spin coupling involving ruthenium-ligand (Ru-L) bonds and other spin-spin interactions obtained from DFT calculations. The proton shift which in close proximity with the Ru and Cl (or O) atoms are characterised with lower and higher chemical shift respectively. Though Ru-Cl bond has longer bond length than all other Ru-L bonds, yet its spin-spin coupling is higher than others because of a very high contribution of PSO which is far higher than the contribution from FC terms. In all other Ru-L bonds, FC is the most significant Ramsey terms that define their spin-spin coupling. Both the isotropic and anisotropic shielding of the Hz of the pyrazole is lower than Hc of the cymene and the spin-spin coupling3J(Hz…Hz) of the pyrazole are less than half of the3J(Hc…Hc) of the cymene unit in the complexes. There is a little increase in both the3J(Hc…Hc) and3J(Hz…Hz) spin-spin coupling in the hydrolysed complexes compare to the non-hydrolysed complexes. The isotropic and anisotropic shielding tensor of Ru atoms increases in magnitude as the complexes get hydrolysed that could be ascribed to a more deshielding chemical environments.

NMR; DFT method; Spin-spin coupling; Interatomic distance; Shielding tensors

Introduction

The coupling constant between a pair of atoms is an important molecular property because it can provide useful information for analysing the structure of a system and the onset of intramolecular bonding interactions[1-2]. Spin-spin coupling is an interaction between the magnetic moments of the coupling nuclei and has been determined experimentally for large number of molecules using classical NMR experiments[3]of the molecules dissolved in liquid crystals[4-5]. The interpretation of experimental spin-spin data is often challenging[3]. J-coupling is sensitive to bonding interactions and is mediated by the polarization of the spins of the intervening bonding electrons unlike direct dipolar coupling, which is a through-space interaction. It has been used to probe the nature of hydrogen bonds, CH—π interactions, as well as van der Waals’ interactions[6]. It is expected that as the number of bonds between the two nuclei increases, their coupling should diminish[1-2].

It is computationally easier to partition the spin-spin property into contributing terms which is experimentally difficult[7]. The nuclear spin-spin coupling (J) of interaction are determined by the four Ramsey terms: Fermi contact (FC), spin dipole (SD), diamagnetic spin orbit (DSO), paramagnetic spin orbit (PSO))[8]. The FC and SD are known to represent the spin polarization densities and describe the interactions of the electronic spin with the nuclear magnetic field (namely the extended dipole field outside the nucleus and a strongly localized field inside the nucleus). The SD coupling mechanism requires occupied and unoccupied non-s-orbitals while FC operator probes the s-electrons at the sites of coupling nuclei[9]. FC operator probes the s-electrons at the sites of coupling nuclei[10]. A decrease of the SD contribution of the multiple bonds, indicating a decrease of the π-character leads to weakening of the bonds[10]. DSO and PSO represents orbital current densities[8]where DSO term is a direct indicator of the anisotropy of the charge distribution centred at the coupling nuclei, bond polarity and the electronegativity difference between two atoms X and Y. The PSO requires occupied and unoccupied non-s-orbitals of the coupling nuclei and can be related to the bond order, π-strength, electronegativity, and the magnetizability of a bond[9].

Our interest in the current study is the magnetic properties of ruthenium complexes starting from the precursor to mono-, bi- and tri-dentate complexes. It is of interest to determine the level of changes in the spin-spin interactions of the Ru-L bonds and their shielding tensors from the precursor to the mono-, bi- and tridentate derivatives of the pyrazole based ligands. It is also necessary to get insights from the theoretical model in relation to the experimental data obtained from their1H-NMR due to the presence of the Cl and Ru atoms and establish the effects of hydration of the complexes on the spin-spin coupling of the Ru-L and the selected C-H and H…H interatomic interactions.

1 Computational methods

Ten ruthenium complexes were optimized using PBEPBE which makes use of the functional of Perdew, Burke and Ernzerhof and their correlation[11-12]. The Ru atom was treated with basis set SBKJC VDZ[13]with effective core potential while all other atoms in the complexes were treated with basis set 6-31+G(d,p)[14-16]. The basis set SBKJC VDZ was obtained from EMSL Basis Set Library[17-18]. The functional PBEPBE which was used for the optimization has been found to give similar results with hybrid functional PBE0 and mPW1PW91 in the optimization of Ru(Ⅱ) complexes and in computing their stationary phase properties[19]. It has also been used to study weak-interacting systems[20]. The only possible limitation is the long-range deficiency of the DFT functional methods especially when studying noncovalent intermolecular interactions which makes hybrid DFT preferable[21-23]. Since we are not considering any long range interactions but purely intramolecular interaction, PBEPBE is thus a good choice. Also, all our geometries optimized with PBEPBE gives zero frequency which is a clear indication that local minimum was obtained through our choice functional method. Also, the basis set SBKJC VDZ ECP with PBE correlation has been shown to be effective in treating complexes with large number of electrons and has been applied in computing properties of many metal clusters[24-25]. The computation of the NMR and NMR spin-spin coupling constants J(A,B)[26-27]were done using B3LYP which is Becke’s three-parameter exchange[28]and Lee-Yang-Parr’s correlation nonlocal functional. During this time, the Ru atom was treated with all electron DGDZVP[29-30]basis set and the GIAO method was used for the computation of the NMR and spin-spin coupling. Both the optimization and computation of the properties were done using Gaussian 09 (G09)[31]. The theoretical proton chemical shift is termed direct method by subtracting each of the proton isotropic shielding directly from that of the reference tetramethylsilane (TMS) and fitting method by using reported equation σ1H=31.0-0.97σ1H as reported in the literature[32].

2 Result and discussion

2.1 The bonds geometries

The geometrical variation especially of the Ru-L bonds and their related angles from the precursor [6h-(Cym)RuCl2]2to monodentate (pzCym, pzWCym), to bidentate (bpzmCym, bpzmWCym, bpzaCym, bpzaWCym) and to tridentate (bpzpyCym, bpzpyWCym) derivatives (Figure 1) are shown in Tables 1 and 2. The complexes Cym2, pzCym,bpzmCym, bpzaCym, bpzpyCym were synthesised but their hydrated forms are only studied computationally.

Fig.1 The molecular representation of precursor dimmer6η-Cymene (Cym2) and6η-Cymene ruthenium(Ⅱ) complexes of pyrazole (pzCym), bis(pyrazol-1-yl)methane (bpzmCym), bis(pyrazol-1-yl)acetic (bpzaCym), bis(pyrazol-1-yl)pyridine (bpzpyCym) and bis(pyrazol-1-yl)pyridinic (bpzpyaCym) derivatives with their hydrated forms. The explicit hydrogen atoms are those whose spin-spin are of interest

Table 1 Selected interatomic distances in Angstroms that define the spin-spin coupling of interesting

The nitrogen atom in Ru-N and Ru-Np represent the coordinating nitrogen atom of the pyrazole and pyridine units of the ligands. The Hc and Hz represent the selected hydrogen atoms from the cymene and pyrazole units respectively.

Table 2 Selected bond angles of interest in the complexes

The computed geometrical bond distance of all the Ru-C ranges from 2.18 (in Cym2) to 2.34 (in bpzpyaCyme and bpzpyCym). The Ru-Cl are found within the range of 2.40 (bpzmCym and bpzaCym) to 2.51 (in precursor WCym2) which fall within many of the experimentally reported range of 2.30 to 2.48 in the literatures for ruthenium crystal structures[33-42]. The bond lengths of the bridged Ru-Cl in the precursor are longer than their normal Ru-Cl bonds. The Ru-Cl bond distances are lower in the complexes bpzmCym and bpzaCym with bidentate compare to other complexes. Uhe presence of the monodentate and bidentate resulted in a longer Ru-O bond distances of the hydrated complexes pzWCym and bpzmWCym (2.24) compare to the precursor WCym2 where the Ru-O bond is lowest (2.20). Among all the Ru-ligand (Ru-L) bonds considered (Ru-C, Ru-Cl, Ru-O and Ru-N), Ru-N has the lowest bond distances which ranges from 2.08 for the Ru-Np (Np is the coordinating nitrogen atom of the pyridine of tridentate ligands) to 2.17 for Ru-N in the complex bpzpyCym. All the Hc…Hc bond distances are within a close range of 2.48 to 2.51. The Hz…Hz have its lowest values in complex bpzpyaCym with tridentates (2.75) and highest values in complex with monodentate (2.78) while reverse is the case of N-N bond distance ranging from 1.35 in complex pzCym with monodentate binding mode to 1.40 in complex bpzpyaCym with tridentate binding modes. There is no change in the C4-H bond distances (1.09) of the pyrazole unit in the complexes and also in the N-Np bond interatomic distance of tridentate.

As expected, the largest bond angle is the Nz-Ru-Nz of the tridentate complexes bpzpyaCym and bpzpyCym but the values is lower than the sum of the two Nz-Ru-Np which are found within the Nz-Ru-Nz of the tridentate complexes. The Nz-Ru-Np bond angle is lower than the Nz-Ru-Np. The Nz-Ru-Nz bond angle is higher in hydrated complexes bpzmWCym and bpzaWCym (Table 2) which is responsible for the observed increase in the N…N bond distances (Table 1) compare to their unhydrated complexes. On the contrary, the Cl-Ru-O bond angle of the hydrated complexes WCym2 and pzWCym are lower than the Cl-Ru-Cl bond angle in their unhydrated complexes.

2.2 NMR chemical shift and spin-spin coupling

The interest is to study the level of changes in the coupling spin-spin interactions of the Ru-L from the precursor to the derivatives and also consider the change in the isotropic shielding tensors of coordinating atoms which are C atoms of cymene, N atoms from the pyrazole derivatives and selected H atoms from the cymene (4H) and pyrazole ligands derivative.

Table 3 The experimental and the theoretical (direct and fitting) of the1H-NMR of the complexes

DirectFittingExperimentCym2CH30.62to3.321.127to3.750.185to3.21C-Hc2.92,4.063.36,4.462.68Cothers-H4.12to5.674.52to6.035.39to5.79pzCymCH30.88to3.281.37to3.710.91to2.80C-Hc3.503.912.84Cothers-H4.59to7.524.98to7.825.47to8.04C4-H6.346.676.52NH12.6012.748.29bpzmCymCH31.17to2.831.66to3.271.10to2.80C-Hc3.714.122.92Cothers-H5.038to8.045.41to8.325.88to8.27CH25.46,6.165.82,6.506.28C4-H6.67,6.696.99,7.016.42bpzaCymCH31.18to2.881.67to3.321.25～1.89C-Hc3.764.173.25Cothers-H5.04to8.085.41to8.314.5to8.47C4-H6.62,6.646.95,6.976.75CHOO7.017.327.45COOH7.567.857.75bpzpyCymCH3-0.52to2.810.014to3.250.351to2.35C-Hc2.442.892.64Cothers-H5.21to8.685.57to8.944.59to8.91C4-H7.32,7.397.63,7.697.05

C-Hc is the CH(CH3)2of the cymene unit

The experimental and theoretical1H-NMR properties of the synthesised complexes are presented in Table 3. As shown in Figure 2, an up-field shift was observed for the four C-H proton of the benzene ring of cymene from the precursor (35.3730) to bpzmCym (35.8779) and to bpzpyCym (35.836) which indicate deshielding effect of the bidentate and tridentate ligands on the cymene proton shift. The assignment of the experimental1H-NMR shift with the values obtained from the theoretical direct and fitting methods are presented in Table 3. There is a strong relationship between the experimental and theoretical chemical shifts especially for the methyl groups, the C4-H of the pyrazole unit and the CH(CH3)2of the cymene protons. The chemical shifts of some methyl groups are very low from negative to values less than one. Through the theoretical analysis of the NMR chemical shifts, it clearly shows that the methyl groups which are characterised with very low chemical shift are directed towards the Ru atom while those with higher chemical shifts are directed towards the chlorido atom in the complexes.

Fig.2 The experimental NMR of the precursor Cem2 and complexes bpzmCym and bpzpyCym derivatives

The values of all the selected spin-spin coupling1J(Ru-L),1J(C-H),1J(N-N*),nJ(N…N) andnJ(H…H) are presented in Table 4 and the feature of their changes in each of the complexes are shown in Figure 3. All the1J(Ru-C),1J(Ru-N) and1J(Ru-Cl) spin-spin interactions have negative values while the1J(Ru-O) andnJ(H…H) have positive values (Table 4 and Figure 2). There is appreciable decrease in the magnitude of the1J(Ru-C) from the precursor (Cym2 and WCym2) to the complexes (Figure 2). The lowest magnitude of the1J(Ru-C) is found in pzWCym (-4.087) while the highest is found in bpzmWCym (-13.317) (Figure 2 and Table 4). In the precursor WCym2 and complex pzWCym where there is another Cl atom after the hydrolysis, the spin-spin interactions of the remaining1J(Ru-Cl) and the1J(Ru-N) decrease significantly in magnitude. The feature of all the1J(Ru-N) of the bpzpyCym and bpzpyaCym are nearly the same with very little or no difference at all. The1J(Ru-Np) of the pyridine unit of bpzpyCym and bpzpyaCym have the lowest magnitude compare to all their1J(Ru-N) of their pyrazole unit. The spin-spin1J(Ru-Cl) have the lowest value in Cym2 and highest value in bpzmCym. The highest value of the spin-spin coupling1J(Ru-O) is found in pzWCym while the lowest is in bpzmWCym. There is no direct relationship between the changes in the bond distances of the complexes and the change in the observed spin-spin coupling values.

Table 4 Selected spin-spin coupling of the complexes

Fig.3 Features of changes in the selected spin-spin coupling of ruthenium(Ⅱ)6η-cymene complexes of pyrazole derivatives and their hydrated forms

The values of all the3J(Hz…Hz) in the pyrazole unit is less than half of the3J(Hc…Hc) spin-spin coupling observed for the cymene unit of the complexes (Table 4). The values of the3J(Hc…Hc) are within the range of 5.947 Hz in pzCyme to 7.230 Hz in complex bpzpyaCym which are within the experimental ranges of 6～8 Hz[43-44], 6[45-46], 5.7～6.2 Hz[47], 6.4 Hz[48], 6.02～6.56 Hz[49]reported in the literatures. The spin-spin range of 7.0～9.2 Hz is more typical of substituted benzenes[50]. The two Ru atoms in Cym2 are very similar in their J-coupling with ligand atoms but there is a relatively higher difference in the two Ru atoms coupling with ligands in WCym2 as a result of the hydrolysis. The J-coupling of the two Ru atoms with their individual Cl atom is higher in negative value than the bridged Cl atoms which is reverse to their observed bond distances (Table 1). There is a little increase in the spin-spin3J(H…H) coupling in the hydrolysed complexes compare to the non-hydrolysed complexes. It is only in the hydrated complex pzWCym that there is a highest1J(Ru-N) spin-spin coupling to its unhydrated complex while no significant change was observed for other hydrated complexes. The4J(N…N) of the spin-spin coupling of the two donor nitrogen atoms of the two pyrazole units is higher than3J(N…Np) between the nitrogen donor centre of the pyrazole unit and the pyridine unit. The lowest spin-spin coupling is the6J(N…N) between the donor nitrogen centre of the pyrazole units of the complexes bpzpzCym and bpzpyaCym. The spin-spin coupling of the C4-H spans a wider range of values ranges from 65.700 Hz of pzWCym to 216.206 of the complex bpzpyCym which is contrary to their observed bond distances which are relatively the same in values (Table 1).

The isotropic and anisotropic shielding tensors of Ru and the C, N, Cl, and O which directly coordinated with it and selected H atoms of interest are shown in Table 5. The isotropic and anisotropic shielding tensor of Ru atoms increases in magnitude as the complexes get hydrolysed which is an indication of more deshielding effect due to hydrolysis. The N atom of the pyridine unit of the tridentate (Np) is much more shielded than the N atoms of its pyrazole units. Among all the coordinating N atoms in the complexes, the N atoms of the pyrazole unit of complexes bpzpyaCym and bpzpyCym have the lowest magnitude of isotropic shielding. Among all the hydrogen atoms of interest (C-H of the cymene unit, C4-H and N-H of the pyrazole unit), the hydrogen atom of N-H have the lowest isotropic shielding but highest anisotropic shielding. Both the isotropic anisotropic shielding of the H atoms of the pyrazole C4-H is lower than that of the cymene C-H. The anisotropic values of the Ru, C, C4, and N atoms are higher than their isotropic shielding especially that of N atom. An opposite is observed for the Hc, Hz and Cl atoms.

Table 5 The Isotropic and Anisotropic shielding of selected atoms of interest in the complexes

2.3 Ramsey terms and their correlation with J-coupling and other computed properties

The values of the Ramsey terms FC, SD, PSO and DSO which determines the J-coupling interactions[8]of selected bonds of interest are presented in supplementary Table S1. In all of the Ru-C, Ru-N, Ru-O, N-N, N…N, Hc…Hc, Hz…Hz, C-H and N-H, the most significant Ramsey term which contribute mostly to their spin-spin interactions is the FC follow by a light contribution from PSO except in all the H…H and C-H where their DSO contribution is higher than PSO. It is possible to relate PSO coupling mechanism to bond order, π-strength, electronegativity, and the magnetizability of a bond[9]. The FC term of the hydrogen atom from pyrazole unit (Hz) is lower than that of the cymene unit (Hc) which resulted to the lower spin-spin coupling of the Hz…Hz of the pyrazole ligands. Unlike other Ru-ligand (Ru-L) bonds, the FC and the PSO contribution to the spin-spin coupling of the hydrated bonds Ru-O are very close in values. The highest values of spin-spin interaction among all the Ru-L bonds are observed in Ru-Cl because of a very high contribution of PSO which is far higher than the contribution from FC term. Generally, the contribution of the Ramsey terms to the values of the spin-spin coupling interaction in the complexes followed the order FC>PSO>SD>DSO. However, there are many exceptions to the order as indicated before. In all the interatomic spin-spin of atoms without a direct bonds like Hc…Hc, Hz…Hz, N…N and two with direct bond (C-H, N-N), the values of SD are significantly lower than DSO indicating the absent of π-character[10]. The reason for higher DSO term than SD term is because DSO is a direct indicator of the anisotropy of the charge distribution centred at the coupling nuclei, bond polarity and the electronegativity difference between two atoms X and Y.

Table 6 The correlations of the Ramsey Terms, Spin-Spin, Isotropic and Anisotropic shielding and their corresponding interatomic distance

FCSDPSODSOJ-CoupFC1.000.330.160.481.00SD0.331.000.920.290.40PSO0.160.921.000.120.24DSO0.480.290.121.000.49J-Coup1.000.400.240.491.00Dist-0.66-0.30-0.13-0.31-0.66Iso10.430.330.340.400.45Aniso1-0.36-0.25-0.25-0.35-0.37Iso2-0.12-0.81-0.87-0.12-0.18Aniso2-0.27-0.45-0.43-0.27-0.30Ave(Iso)0.430.220.220.400.44Ave(Aniso)-0.36-0.27-0.26-0.35-0.38

Fig.4 The correlation (R2) and linear equation of the Ramsey terms, Isotropic, Anisotropic, average Isotropic and Anisotropic shielding tensor with the J-Coupling of selected atoms in the complexes. The J-coupling and FC were scaled with 0.1; Iso1, Aniso1, Ave(Iso) and Ave(Aniso) were scaled by 0.001 while Iso2 and Aniso2 were scaled by 0.01 in the plot. The suffix 1 and 2 of the Iso and Aniso indicate first and second atom that are involved in the coupling

The correlation of the J-coupling interaction with the Ramsey terms, interatomic distance, atomic isotropic and anisotropic shielding are shown in Table 6. The most correlating Ramsey terms with spin-spin coupling is FC (R2=0.99 as shown in Figure 4) just has its values are found to be significant. Even though the values of PSO are significant in many of the computed spin-spin coupling than SD and DSO but its correlation with the spin-spin coupling is lower than that of SD and DSO. There is significant high correlation of the interatomic distances with both the FC and spin-spin coupling. There is significant correlation between the FC and PSO just as the two of them are found to be the most significant in values among the computed Ramsey terms for the bonds. Even though the values of interatomic distances do not directly determine the interatomic spin-spin coupling but its correlation with spin-spin coupling is higher (R2=0.43 as shown in Figure 4) than PSO, SD and DSO which directly determine the values. The correlation of the isotropic and anisotropic shielding tensor of the first set of atom which is dominated with Ru atom and that of the second sets and their averages with the spin-spin coupling is lower than many of the Ramsey terms like FC and DSO.

3 Conclusions

The chemical shift and the spin-spin coupling interaction of ten ruthenium complexes made up of six non-hydrated and four hydrated forms were computed using DFT calculations. Four of the non-hydrated complexes were synthesised and a high similarity between the experimental and theoretical prom NMR chemical shifts were observed especially for their methyl groups, the C4-H of the pyrazole unit and the CH(CH3)2of the cymene protons. The methyl groups which are characterised with very low chemical shift are directed towards the Ru atoms while those with higher chemical shift are directed towards the chlorido atom in the complexes. The bond length of the bridged Ru-Cl in the precursors are longer than their normal Ru-Cl bonds while J-coupling bridged is lower than the normal. The Ru-Cl bond distances are lower in the complexes bpzmCym and bpzaCym with bidentate compare to other complexes. The highest values of spin-spin interaction among all the Ru-L bonds are observed in Ru-Cl because of a very high contribution of PSO which is far higher than the contribution from FC term. Among all the Ru-ligand (Ru-L) bonds considered, Ru-N has the lowest bond distances but the spin-spin of Ru-N falls in between that of Ru-C and Ru-Cl. The interatomic distance Hc…Hc of the cymene unit are within a close range in all the complexes but less than Hz…Hz of the pyrazole unit. Both the isotropic and anisotropic shielding of the Hz of the pyrazole is lower than Hc of the cymene. All these can contribute to lower spin-spin coupling of3J(Hz…Hz) which is less than half of the3J(Hc…Hc) of the cymene unit of the complexes. The FC term of the hydrogen atom from pyrazole unit (Hz) is lower than that of the cymene unit (Hc) which resulted to the lower spin-spin coupling of the Hz…Hz of the pyrazole ligands. There is a little increase in both the3J(Hc…Hc) and3J(Hz…Hz) spin-spin coupling in the hydrolysed complexes compare to the non-hydrolysed complexes. The Nz-Ru-Nz bond angle is higher in hydrated complexes bpzmWCym and bpzaWCym which is responsible for their observed increase in the N…N bond distances (Table 1) compare to their unhydrated complexes. The4J(N…N) of the spin-spin coupling of the two donor nitrogen atoms of the two pyrazole units is higher than3J(N…Np) between the nitrogen donor centre of the pyrazole unit and the pyridine unit. All the1J(Ru-C),1J(Ru-N) and1J(Ru-Cl) spin-spin interactions have negative values while the1J(Ru-O) andnJ(H…H) have positive values. There is appreciable decrease in the magnitude of the1J(Ru-C) from the precursor (Cym2 and WCym2) to the complexes. The isotropic and anisotropic shielding tensor of Ru atoms increases in magnitude as the complexes get hydrolysed which an indication of more deshielding effect due to hydrolysis. In all of the Ru-C, Ru-N, Ru-O, N-N, N…N, Hc…Hc, Hz…Hz, C-H and N-H, the most significant Ramsey term which contribute mostly to their spin-spin interaction is the FC follow by a light contribution from PSO except in all the H…H and C-H where their DSO contribution is higher than PSO. The most correlating Ramsey terms with spin-spin coupling is FC while the correlation of inteatomic distances with spin-spin coupling is higher than other Ramsey terms.

Acknowledgements： Authors gratefully acknowledged the financial support of Govan Mbeki Research and Development Centre, University of Fort Hare, South Africa. The CHPC in Republic of South Africa is acknowledged for providing the computing facilities and some of the software’s that were used for the computation.

[1] Stanford M W, Knight F R, Arachchige K S A, et al. Dalton Trans.，2014，43： 6548.

[2] Ernst L, Sakhaii P. Magn. Reson. Chem., 2000，38： 559.

[3] Del Bene J E, Elguero J, Alkorta I. J. Phys. Chem., 2004, A108: 3662.

[4] Del Bene J E, Alkorta I, Elguero J. J. Phys. Chem., 2009，A113： 12411.

[5] Autschbach J, Kantola A M, Jokisaari J. J. Phys. Chem., 2007，A111： 5343.

[6] Perras F A, Bryce D L. J. Magnetic Resonance, 2014, 242: 23.

[7] Del Bene J E D, Alkorta I, Elguero J. J. Phys. Chem., 2010，A114： 2637.

[8] Cremer D, Grafenstein J. Phys. Chem. Chem. Phys., 2007，9： 2791.

[9] Gaur R, Mishra L. Inorg. Chem., 2012，51： 3059.

[10] Pratuangdejkul J, Jaudon P, Ducrocq O C, et al. J. Chem. Theory Comput.，2006，2： 746.

[11] Perdew J P, Burke K, Ernzerhof M. Phys. Rev. Lett., 1996，77： 3865.

[12] Perdew J P, Burke K, Ernzerhof M. Phys. Rev. Lett., 1997，78： 1396.

[13] Stevens W J, Krauss M, Basch H, et al. Can. J. Chem., 1992，70： 612.

[14] Ditchfield R, Hehre W J, Pople J A. J. Chem. Phys., 1971，54： 724.

[15] Hehre W J, Ditchfield R, Pople J A. J. Chem. Phys., 1972，56： 2257.

[16] Gordon M S. Chem. Phys. Lett., 1980，76： 163.

[17] Feller D J. Comp. Chem.，1996, 17(13)： 1571.

[18] Schuchardt K L, Didier B T, Elsethagen T, et al. J. Chem. Inf. Model.，2007，47： 1045.

[19] Kusama H, Funaki T, Sayama K. J. Photochem. and Photobio. A: Chem.，2013，272： 80.

[20] Li Z Y, Wang H L, He T J, et al. Theochem., 2006，778： 69.

[21] Adamo C, Barone V. J. Chem. Phys., 1998，108： 664.

[22] Pejov L, Solimannejad M, Stefov V. Chem. Phys., 2006，323： 259.

[23] Kusama H, Sayama K. J. Phys. Chem., 2012，C116： 23906.

[24] Marchal B, Carbonniére P, Begue D, et al. Chem. Phys. Letters, 2008，453： 49.

[25] Marchal R, Carbonnière P, Pouchan C. Comput. Theoret. Chem.，2012，990： 100.

[26] Helgaker T, Watson M, Handy N C. J. Chem. Phys., 2000，113： 9402.

[27] Sychrovsky V, Grafenstein J, Cremer D. J. Chem. Phys., 2000，113： 3530.

[28] Becke A D. J. Chem. Phys., 1993，98： 5648.

[29] Godbout N, Salahub D R, Andzelm J, et al. Can. J. Chem., 1992，70： 560.

[30] Sosa C, Andzelm J, Elkin B C, et al. J. Phys. Chem.，1992，96： 6630.

[31] Frisch M J, Trucks G W, Schlegel H B, et al. Gaussian Inc, Wallingford CT, 2009.

[32] Sanz D, Claramunt R M, Alkorta I, et al. Magn. Reson. Chem.，2012，50： 246.

[33] Cebrian-Losantos B, Reisner E, Kowol C R, et al. Inorg. Chem., 2008，47： 6513.

[34] David S, Perkins R S, Fronczek F R, et al. J. Inorg. Biochem., 2012，111： 33.

[35] Al-Noaimi M, AlDamen M A. Inorganica Chimica Acta, 2012，387： 45.

[36] Türkoglu G, Tampier S, Strinitz F, et al. Organometallics，2012，31： 2166.

[37] Gaur R, Mishra L. Inorg. Chem.，2012，51： 3059.

[38] Nakajima K, Ando Y, Mano H, et al. Inorganica Chimica Acta, 1998，274： 184.

[39] Renfrew A K, Phillips A D, Tapavicza E, et al. Organometal, 2009, 28: 5061.

[40] Lua Z L, Eichelea K, Warada I, et al. Allg. Chem., 2003, 629: 1308.

[41] Dutta B, Solari E, Gauthier S, et al. Organometallics，2007，26： 4791.

[42] Dutta B, Scopelliti R, Severin K. Organometal, 2008, 27: 423.

[43] Shang X, Silva T F S, Martins L M D R S, et al. J. Organomet. Chem., 2013，730： 137.

[44] Dell’Amico D B, Calderazzo F, Labella L, et al. J. Organomet. Chem., 2002，651： 52.

[45] Melchart M, Habtemariam A, Parsons S, et al. Inorganica Chimica Acta, 2006, 359: 3020.

[46] Caruso F, Rossi M, Benson A, et al. J. Med. Chem., 2012，55： 1072.

[47] Vock C A, Scolaro C, Phillips A D, et al. J. Med. Chem.，2006，49： 5552.

[48] Canivet J, Karmazin-Brelot L, Suss-Fink G. J. Organomet. Chem., 2005，690： 3202.

[49] Betanzos-Lara S, Salassa L, Habtemariam A, et al. Organometallics，2012，31： 3466.

[50] Katritzky A R, Akhmedov N G, Guven A, et al. J. Mol. Struc., 2006，783： 191.

O433

A

10.3964/j.issn.1000-0593(2016)11-3737-09

Received： 2015-11-02; accepted： 2016-02-08

e-mail: pajibade@ufh.ac.za; ajibadepeters@gmail.com