XU Hui-Ying CAO Shng-WiWANG Wi ZHU Jin-QingZOU Jin-Wi XU Xio-Lu LU Yin

?

Investigation of the Substituent Effects on-Type Pnicogen Bond Interaction①

XU Hui-Yinga②CAO Sheng-WeibWANG WeicZHU Jian-QingdZOU Jian-WeieXU Xiao-Lua②LU Yina

a(310015)b(322118)c(310008)d(310015)e(315104)

Intermolecular interactions between PH2Cl and Ar–R (R = H, OH, NH2, CH3, Br, Cl, F, CN, NO2) were calculated by using MP2/aug-cc-pVDZ quantum chemical method. It has been shown from our calculations that the aromatic rings with electron-withdrawing groups represent much weaker binding affinities than those with electron-donating groups. The charge-transfer interaction between PH2Cl and Ar–R plays an important role in the formation of pnicogen bond complexes, as revealed by NBO analysis. Nevertheless, AIM analysis shows that the nature of the interactions between PH2Cl and Ar–R is electrostatic, and the interaction energies of the complexes are correlated positively with the electron densities in the bond critical points (BCPs). RDG/ELF graphical analyses were performed to visualize the positions and strengths of the pnicogen bonding, as well as the spatial change of the electron localization upon the formation of complexes. The-type halogen bond was also calculated, and it has been revealed that the-type pnicogen bond systems are more stable than the halogen bond ones.

-type pnicogen bonding,-type halogen bonding, NBO, AIM, RDG/ELF analysis;

1 INTRODUCTION

Molecular interaction, closely correlated to various physicochemical properties, life phenomena and material structures, has been of great concern in physics, chemistry, biology, material science and some other fields[1-5]. The hydrogen bond interaction is of typical molecular interaction[6]. Then, the halogen bond[7], lithium bond[8]and other weak interaction were found. In 2009, Hey-Hawkins et al[9]proved the existence of P×××P non-bond interaction via13C {1H,31P} NMR experiment. Scheiner[10-15]theoretically calculated the geometrical structure and interaction energy of a series of pnicogen bond systems including P×××P, N×××P, etc. Since then, the research on pnicogen bond interaction has attracted the attention of theoretical and experimental che- mists[16-20]. Recently, Zukerman-Schepector et al[21]emphatically discussed the As×××interaction of the supermolecular system, searched out 20 structures involved with the As×××interaction from the CSD (Cambridge Structural Database), and concluded the importance of As×××interaction in supermolecular construction from these characteristic structures. Based on the achievement of Zukerman-Schpector, et al, the interaction was calculated between ECl3(E = As, Sb, Bi) andelectron donors (e.g. benzene, hexafluorobenzene) by Frontera subject team[22], and the significance of-type pnicogen bond in the life science field was explored. PH3is the simplest pnicogen-bond donor molecule with a weak pnicogen bond interaction. However, when one of the H atoms is replaced by Cl atom (PH2Cl), the P×××N pnicogen bonding interaction formed between PH2Cl and the representative electron donor NH3even exceeds the hydrogen bond interaction between water molecules[23], so PH2Cl is often used as the model molecule in the research on pnicogen bond interaction[24, 25]. In this paper, the interactions between PH2Cl and the substituted benzene (Ar–R, R= H, OH, NH2, CH3, Br, Cl, F, CN, NO2) are calculated using the quantum chemistry method, aiming to explore the geometrical structure, electronic structure and interaction energy of-type pnicogen bond between PH2Cl and the aromatic compound. Furthermore, the effects of the substituting group in the aromatic ring to the stability of-type pnicogen bond complex are considered, in order to provide a theoretical basis for recognizing the nature of-type pnicogen bonds.

2 COMPUTATIONAL METHODS

3 RESULTS AND DISCUSSION

3. 1 Geometrical structure and interaction energy

The stable structures of the complexes combining PH2Cl with substituted aromatic compounds are obtained at the level MP2/aug-cc-pVDZ, and the geometrical structures are shown as Fig. 1. As can be seen from these geometrical structures in Fig. 1, the pnicogen bond interaction is generated between the P atom in PH2Cl and the-electron in the aromatic ring. According to our aforesaid definitions[31], theangle is the included angle between the vector from the P atom to the hetero ring centroid and the vector at the P–Cl bond direction (see Fig. 2), and the values of anglefor complexes 1～9 are shown in Table 1. The anglevalues of 8 complexes are almost 180° except that of complex 3, i.e. the three points of Cl, P, and the centroid are almost at the same straight line. The optimization result for complex 3 shows that one of the H atoms (H17) in PH2Cl is also close to the aromatic ring center, i.e. a certain-type hydrogen bond interaction is formed between the atom H in PH2Cl and the-electron in the aromatic ring, so the decrease of angleis caused by the interference of interaction P(15)–H(17)···.

Fig. 1. Optimized geometries of complexes at the MP2/ aug-cc-pVDZ level

Fig.2. Geometric model of the pnicogen bonded angle

Table 1. Geometric Parameters and Interaction Energies of the Complexes at the MP2/aug-cc-pVDZ levela

aInteraction energies are given in kcal·mol?1.

Fig.3. Molecular graphs of PH2Cl…Ar–H and PH2Cl…Ar–OH and electrostatic potential surface of monomers PH2Cl

3. 2 NBO analysis

Table 2 shows the donor-acceptor orbital, the second-order perturbation stabilization energy (Δ2), and the charge transfer quantum (CT) of 9-type pnicogen bond complexes at the level MP2/aug- cc-pVTZ. The second-order perturbation stabilization energy (Δ2) can be obtained from the following equation:

Table 2. Natural Bond Orbital Analysis of Complexes 1～9 at the MP2/aug-cc-pVDZ Level

According to the data in Table 2, the correlation between the second-order perturbation stabilization energy of the C–Cbonding orbital and theanti-bonding orbital of P–Cl and the corrected interaction energy are mapped in Fig. 4(a), and the following relational expression is obtained after fitting:

= 0.956, SD = 0.527,= 9

Fig.4. Relationship between the second-order perturbation stabilization energy and interaction energy

The molecular interaction is always accompanied by charge transfer, whose quantities in complexes 1～9 are shown in Table 2. As seen in the table, the charge quantities transferred from the aromatic compound to PH2Cl molecule are from 6 to 16me. The charge quantity transferred is not so much, and it complies with the soft acid-soft alkali model (PH2Cl molecule as the soft acid and the aromatic compound as the soft alkali). The plot of the charge transfer quantity and the corrected interaction energy is shown in Fig. 5. The curvilinear equation is as below:

106824.298 (QCT)2

Fig.5. Relationship between charge transfer and interaction energy

3. 3 AIM analysis

To further analyze the nature of-type pnicogen bond interaction, the AIM (Atom in Molecule) theory developed by Bader is used, as the theory is often used in researches on molecular weak interac- tions[32-35]. The typical pnicogen bond complex molecular diagram has been shown in Fig. 6, in which a critical point between the atom P and the aromatic ring is observed, and therefore the existence of-type pnicogen bonds is proved. Table 3 shows the electron densities (ρ), Laplacian of electron densities (?2ρ), three eigenvalues (1,2,3) of Hessian matrix, kinetic energy densities (), potential energy densities () and electronic energy density () of the 9-type pnicogen bond complexes at the bond critical point of pnicogen bond (BCP) at the MP2/aug-cc-pVDZ level.

According to the AIM theory, charges are dispersed and the bond ionicity is stronger at BCP when |1+2| <3and?2b> 0, but charges are centralized and the bond covalence is stronger when |1+2| >3and?2b< 0. The data in Table 3 suggest that, the Laplacian quanta (?2b) at BCP are larger than zero and |1+2| <3, which means the ionicity of-type pnicogen bond is stronger in complexes 1～9. The electronic energy densityb(sum of the kinetic energy densityband the potential energy densityb) is often deemed as a correct index for understanding the weak interaction[36, 37]. The interaction is a static interaction whenb> 0, and is a covalence interaction whenb< 0. Allbvalues in Table 3 are larger than zero, which means that the interactions of the 9-type pnicogen bond com- plexes belong to the static interaction, and it com- plies with the above conclusion that “charges are dispersed and the bond ionicity is stronger at BCP when |1+2| <3and?2b> 0”. The electron density (b) at BCP is correlated to the bond strength, as the bond strength is larger if the electron density is higher. The relationship of the electron density (b) at BCP and the corrected interaction energy of the complex is mapped (Fig. 7), and the correlation coefficientis 0.915.

Table 3. Topological Parameters of Complexes 1～9 at the BCP Pointb

bTopological parameters are given in a.u.

Fig.6. Molecular graphs of complexes 1 and 2

Fig.7. Relationship between the electron density at BCPs and the interaction energy

3. 4 RDG/ELF analysis

Yang Weitao’s subject team[38]has developed a visualized method for the weak interaction research, through which the calculated values of reduced density gradient (RDG) function and sign (2(r))() of each point in the space are visualized in the RDG isosurface map. The gradient isosurfaces are colored according to the corresponding values of sign (2(r))(), which is found to be a good indicator of interaction strength. We used this method in analy- zing the position and strength of the interaction between hydrogen bonds, halogen bonds and pnicogen bonds and the coordination bond, and the result was promising[39-41]. The electron localization function (ELF) is an important tool for electron structure researches, and it is often used to study chemical problems[42]such as the molecular interac- tion. These two analysis methods are applied to-type pnicogen bond interaction in order to visua- lize the interaction change.

Fig. 8 shows the isosurface map for complexes 1 and 2 obtained from the combination of RDG and ELF (Fig. 8a) and the electron localization isosurface map of PH2Cl (Fig. 8b). In the case, the spatial position of molecular interaction can be expected, and the interaction strength is also observed according to the color of RDG map, in which blue represents the strong interaction, green the weak interaction, and red the repulsion. Comparing the color-filled RDG isosurface maps for complex 1 and complex 2, we can find the blue zone of complex 2 is deeper than that of complex 1, which suggests complex 2 has stronger pnicogen bond interaction than 1. The white column and vacuum ring zones in Fig. 8a represent the localization spaces of the lone-pair electron,electron and valence electron. The localization space ((P)) of the lone-pair electron on the atom P is obviously weakened (Fig. 8b). The reason for such phenomenon is that the intermolecular distance is shortened by the weak interaction, and some repulsion is generated betweenelectron and the lone-pair electron on the atom P. Such weak interaction force shortening the inter- molecular distance is mainly the static interaction. According to the AIM analysis, the pnicogen bond interaction is mainly the static acting force. In other words, what is weakening the lone-pair electron localization space on P atom is the pnicogen bond interaction to a certain extent.

Fig.8. (a) RDG/ELF isosurface map of complexes 1 and 2; (b) ELF isosurface map (= 0.9) of PH2Cl

4 CONCLUSION

The geometrical structural optimization, energy calculation and topological and graphic analyses for the various pnicogen bond system of PH2Cl and Ar–R (R = H, OH, NH2, CH3, Br, Cl, F, CN, NO2) have been made at level MP2/aug-cc-pVDZ. The results showed that the complex pnicogen bond interaction is strengthened when the substituting group in the benzene ring is the electron donating group, and the complex pnicogen bond interaction is weakened when the substituting group is the electron withdrawing group. To compare the interaction energy of the-type pnicogen bond system with the halogen bond system, the interaction energy of-type halogen bond system is also calculated, and it is showed that the-type pnicogen bond system is more stable. NBO theory is used to analyze the correlation between the second-order perturbation stabilization energy and the charge transfer quantum with the interaction energy, and the result shows that the charge transfer plays an important role in the stability of the pnicogen bond complex. AIM analysis has indicated that, the nature of pnicogen bond interaction is the electrostatic interaction, and the electron density at BCP is positively correlated to the interaction energy of the pnicogen bond complex. RDG analysis showed the position and strength of pnicogen bond interaction, and ELF analysis indicated the change of lone-pair electron locali- zation space on P atom after the complex formation.

(1) Nguyen, H. L.; Horton, P. N.; Hursthouse, M. B.; Legon, A. C.; Bruce, D. W. Halogen bonding: a new interaction for liquid crystal formation.2004, 126, 16–17.

(2) Baiocco, P.; Colotti, G.; Franceschini, S.; Ilari, A. Molecular basis of antimony treatment in Leishmaniasis.. 2009, 52, 2603–2612.

(3) Gillet, N.; Chaudret, R.; Contreras-García, J.; Yang, W.; Silvi, B.; Piquemal, J. Coupling quantum interpretative techniques: another look at chemical mechanisms in organic reactions..2012, 8, 3993–3997.

(4) Mahadevi, A. S.; Sastry, G. N. Cation-interaction: its role and relevance in chemistry, biology,and material science..2013, 113, 2100–2129.

(5) Schneider, H. J. Binding mechanisms in supramolecular complexes.2009, 48, 3924–3977.

(6) Qu, R. J.; Liu, H. X.; Feng, M. B.; Yang, X.; Wang, Z. Y. Investigation on intramolecular hydrogen bond and some thermodynamic properties of polyhydroxylated anthraquinones.2012, 57, 2442–2455.

(7) Wash, P. L.; Ma, S.; Obst, U.; Rebek, J. J. Nitrogen-halogen intermolecular forces in solution.1999, 121, 7973–7974.

(8) Ault, B. S. Infrared spectra of argon matrix-isolated alkali halide salt/water complexes.1978, 100, 2426–2433.

(9) Bauer, S.;Tschirschwitz, S.; L?nnecke, P.; Frank, R.; Kirchner, B.; Clarke, M. L.; Hey-Hawkins, E. Enantiomerically pure bis(phosphanyl)carbaborane(12) compounds.2009, 19, 2776–2788.

(10) Scheiner, S. A new noncovalent force: comparison of P···N interaction with hydrogenand halogen bonds.. 2011, 134, 094315~1–094315~9.

(11) Scheiner, S. Can two trivalent N atoms engage in a direct N···N noncovalent interaction?2011, 514, 32–35.

(12) Scheiner, S. On the properties of X···N noncovalent interactions for first-, second-, andthird-row X atoms.2011, 134, 164313~1–164313~9.

(13) Adhikari, U.; Scheiner, S. Comparison of PD (D = P, N) with other noncovalent bonds in molecularaggregates.. 2011, 135, 184306~1–184306~10.

(14) Scheiner, S.; Adhikari, U. Abilities of differentelectron donors (D) to engage in a P···D noncovalent interaction.2011, 115, 11101–11110.

(15) Scheiner, S. Weak H-bonds: comparisons of CH···O to NH···O in proteins and PH···N to direct P···N interactions.2011, 13, 13860–13872.

(16) Del Bene, J. E.; Alkorta, I.; Sa?nchez-Sanz, G.; Elguero, J. Structures, binding energies, and spin-spin coupling constants of geometric isomers of pnicogen homodimers (PHFX)2, X = F, Cl, CN,CH3, NC.2012, 116, 3056–3060.

(17) Del Bene, J. E.; Alkorta, I.; Sa?nchez-Sanz, G.; Elguero,J. Homo- and heterochiral dimers (PHFX)2, X = Cl, CN, CH3, NC: to what extent dothey differ?. 2012, 538, 14–18.

(18) Alkorta, I.; Sa?nchez-Sanz, G.; Elguero, J.; Del Bene, J. E. Exploring (NH2F)2, H2FP:NFH2, and (PH2F)2potential surfaces: hydrogen bonds or pnicogen bonds?2013, 117, 183–191.

(19) Scheiner, S. Sensitivity of noncovalent bonds to intermolecular separation: hydrogen, halogen, chalcogen, and pnicogen bonds2013, 15, 3119–3124.

(20) Bauzá, A.;Qui?onero, D.; Deya` P. M.; Frontera,A. Halogen bonding versus chalcogen and pnicogen bonding: a combined Cambridge structural database and theoretical study.2013, 15, 3137–3144.

(21) Zukerman-Schpector, J.; Otero-de-la-Roza, A.; Lua?a, V.; Tiekink, E. R. T. Supramolecular architectures based on As(lone pair) ···(aryl) interactions..2011, 47, 7608–7610.

(22) Bauzá, A.;Qui?onero, D.; Deyà, P. M.; Frontera, A. Pnicogen-complexes: theoretical study and biological implications.2012, 14, 14061–14066.

(23) Scheiner, S. Effects of substituents upon the P···N noncovalent interaction: the limits of its strength.2011, 115, 11202–11209.

(24) Liu, X.; Cheng, J.; Li, Q.; Li, W. Competition of hydrogen, halogen, and pnicogen bonds in thecomplexes ofHArF with XH2P (X = F, Cl, and Br)2013, 101, 172–177.

(25) Adhikari, U.;Scheiner, S. Sensitivity of pnicogen, chalcogen, halogen and H-bonds to angular distortions.. 2012, 532, 31–35.

(26) Frisch, M. J.; Trucks G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Hallacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chen, W.; Wong, M. W.; Andres J. L.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A., Gaussian, Inc., Wallingford CT 2003.

(27) Scheiner, S. Effects of multiple substitution upon the P···N noncovalent interaction.2011, 387, 79–84.

(28) Adhikari, U.;Scheiner, S. Effects of carbon chain substituents on the P···N noncovalent bond.2012, 536, 30–33.

(29) Boys, S. F.; Bernardi, F. The calculation of small molecularinteractions by the differences of separatetotal energies. Some procedures withreduced errors.1970, 19,553–566.

(30) Lu, T.; Chen, F. W. Multiwfn: a multifunctional wavefunction analyzer.. 2012, 33, 580–592.

(31) Xu, H. Y.;Wang, W.; Zou,J. W. Theoretical study of pnicogen bonding interactions between PH2X and five-membered heterocycles.2013, 71, 1175–1182.

(32) Popelier, P. L. A.Characterization of a dihydrogen bond on the basis of the electron density.1998, 102, 1873–1878.

(33) Grabowski, S. J.calculations on conventional and unconventional hydrogen bonds study of the hydrogen bond strength.2001, 105, 10739–10746.

(34) Scheiner, S.;Grabowski,S. J.; Kar, T. Influence of hybridization and substitution on the properties of the CH···O hydrogen bond.2001, 105, 10607–10612.

(35) Wang, W. Z. Halogen bond involving hypervalent halogen: CSD search and theoretical study.2011, 115, 9294–9299.

(36) Lu, Y. X.; Zou, J. W.; Wang, Y. H.; Yu, Q. S.and atoms in molecules analyses of halogen bondingwith a continuum of strength.2006, 776, 83–87.

(37) Lu, Y. X.; Zou, J. W.; Wang, Y. H.; Yu, Q. S. Theoretical investigations of the C-X/interactions betweenbenzene and some model halocarbons..2007, 334, 1–7.

(38) Johnson,E. R.; Keinan, S.; Mori-Sánchez, P.; Contreras-García, J.; Cohen, A. J.; Yang, W. T. Revealing noncovalent interactions..2010, 132, 6498–6506.

(39) Xu,H. Y.; Wang, W. Interaction between Mg-porphyrin and nitrogen, oxygen heterocyclic compounds.. 2011, 27, 2565–2570.

(40) Xu, H. Y.;Wang, W.; Xu, X. Y. Molecular recognition of pyromellitic imide-azacyclophane to organic pollutant.2012, 31, 591–598.

(41) Xu, L.; Lv, J.; Sang, P.; Zou, J. W.; Yu, Q. S.; Xu, M. B. Comparative insight into the halogen bonding of 4-chloropyridine and itsmetal [CuI, ZnII] coordinations with halide ions: a theoretical study on M–C–X···X'.2011, 379, 66–72.

(42) Grabowski, S. J. What is the covalency of hydrogen bonding?2011, 111, 2597–2625.

5 June 2017;

13 October 2017

the Science and Technology Project of Zhejiang Province (2016C33039), Natural Science

Foundation of Zhejiang Province (LY14C030004), National Natural Science Foundation of China (21272211), Project of the Special Foundation for Provincial Research Institutes of Zhejiang Province, China (2017F50002), and Science and Technology Planning Project of the Zhejiang Provincial Department of Water Resources (RB1608)

E-mails: xuhy65@163.com and xxlhz2008@163.com

10.14102/j.cnki.0254-5861.2011-1745