摘要:
Dihydrogen bonds (A-H-H-B) Ibon Alkorta,*a Jose Elguerw and Concepcion Foces-Foces*b a Instituto de Quimica Mtdica, CSIC, Juan de la Cierva, 3, E-28006 Madrid, Spain Departamento de Cristalografia, Instituto de Quimica-Fisica 'Rocasolano' ,CSIC, Serrano, I 19, E-28006 Madrid, Spain Theoretical calculations up to MP216-31G** with BSSE correction are carried out on a series of A-Ha-H-B dihydrogen bonds (A = B, Li, Be; B = N, C). Classical hydrogen bonds (HBs) (A-H-B) where A and B are heteroatoms (generally F, 0 and N atoms)' have been generalized in three ways: HBs with unconventional donors (C-H);2-4 HBs with unconventional acceptors (n-bonded functional groups,3 Cl,5 F,6 C atoms7), and much more daring, dihydrogen bonds A-H-..H-B (designated DHB).8,9 Crabtree and co-workers8 reported 26 intermolecular DHBs of the type B-H-m-H-N with dHH < 2.2 8, in 18 X-ray crystal structures from the Cambridge Structural Database (CSD);lO in most cases, the N-H bonds correspond to N+-H groups.These authors have studied the system (H3BNH3)2 at the PCI- 8O/B3LYP level, finding that the Mulliken charges on the hydrogen involved in the DHB were +0.27 and -0.09 e for N-H and B-H respectively. Epstein and co-workers experimentally addressed the problem of intermolecular DHBs in solution.9 We report here a computational approach and the experi- mental verification of other DHBs. We started from the simple idea that these situations require two hydrogen atoms with opposite charges. Following Crabtree and Siegbahn, we will use as criteria to establish the existence of a DHB the interaction energy [AE = E(A-Ha-H-B) -E(A-H) -E(B-H)] and the H..-H distance. Crabtree and Siegbahn used, for the H--H distance, a limit of 2.4 8, as the sum of the van der Waals radii of two hydrogen atoms.8 We prefer to use 2.7 A which is the calculated value (RHF/6-3 1 l++G**) for H3C-H-.H-CH3 [AE = 0.2 kcal mol-1 (cal = 4.184 J)]." We have selected as compounds with 'acid' hydrogen atoms NH4+ (0.414 e) (Mulliken charges in parentheses), HCN (0.268 e) and H-CrC-H (0.233 e); as representative compounds with 'basic' hydrogen atoms BH4- (-0.272 e), LiH (-0.193 e), BeH2 (-0.109 e), and finally CH4 (0.1 18 e) as an 'amphoteric compound'.12 The calculations have been performed using the Gaussian- 92l3 and Gaussian-9414 sets of programs.All the molecular complexes have been fully optimized with the 6-3 1G**'S and 6-3 1 1++G**I6 basis sets at the HF and MP217 levels of theory. The frequencies of all complexes have been evaluated at the RHF/6-31G** level to confirm the minimum nature of the structures. The interaction energies have been corrected for the inherent basis set superposition error (BSSE) using the Boys- Bernardi counterpoise technique.18 The DHBs have been characterized using the topological analysis of the electronic charge density19 with the AIMPAC program package.20 The results are gathered in Tables I (energies) and 2 (geometries). The theoretical results show two possible dispositions of dihydrogen bonds, nonlinear (1 and 2) in which three H--H interactions are present and linear (3 and complexes with C,, symmetry).The linear arrangement for the systems of the first case has been optimized and yields structures, which are not minima of the potential surface, with shorter H..-H distances (for instance 1.709 8, for BH4--..HCN, 2.12 1 8, for CH4--NH4+ and 2.446 8, for BH4-.-CH4 calculated with the 6-31G** basis set). We have tried some relationships between the interaction energies AE and the Mulliken populations of the hydrogen atoms of the isolated monomers (RHF/6-31 l++G**); for instance, AE = 45546 (f840) [(qA-H) x (q&H>l3,n = 7, r2 = 0.998 (excluding the CH4..-NH4+ complex). This equation predicts for the complex (BH4-...NH4+) a AE = -106.5 kcal mol- .21 The charge density at the hydrogen bond critical points, pc, shows large electronic densities and positive values of v2p which indicate strong hydrogen bonds (Fig.1 shows the plot of V2p for the BeH2--NH4+ complex). There is a rough relation- ship between AE and pc: AE = 678.7 pc,n = 8, r2 = 0.89. To check if these DHBs correspond to real situations we have explored the CSD.10 We have retrieved those of type B-H-eH- N reported previously;8 moreover other situations have been found: B-Ha--H-0, B-H-aH-C where C is an aliphatic sp3 C atom or an aromatic ring (Mulliken population for benzene qH = 0.148 e) and Al-H.-H-C where C belongs to the CH2 of tetraethylammonium cation (Mulliken population for the CH of CH3-NH3+ qH = 0.222 e).To illustrate these findings we have selected four examples (CSD refcode and name in parentheses): B-H.m.H-0, H***H2.19 A, B-H--*H 151", H-e-H-0 125", B- H.-H-O torsion -109" [KUMFED, tetrapotassium 7,6-bideca- boryl( 18) dihydrate]; B-H-.H-C(sp3), Ha-H 2.02 A,B-H-H 128O, H-..H-C(sp3) 159", B-H--H-C(sp3) torsion 130" [BOR- MUQO 1, bis(tripheny1phosphine)iminium heptahydroborate dichloromethane solvate]; B-H-.H-C(ar), H--H 1.75 A, B-H-.H 159O, H.--H-C(ar) 155O, B-H.-H-C(ar) torsion -62" { WAGBAH, (R)-(-)-N-methyl, N-[lR,2S)- 1 -(alphahydroxy- benzyl)ethyl]amino(methyl)phenylphosphine borane]; Al-Table l Interaction energies, AE (kcal mol-l), and values of the charge density at the hydrogen bond critical point pc(e ao-3) System 6-31G**~ 6-31G**' 6-31 l++G**h MP2/6-31G**' pc' -18.50 -18.02 -17.02 -18.03 0.018 -1.80 -1.37 -1.20 -1.88 0.007 -46.35 -38.60 -38.08 -0.046d -7.72 -7.42 -7.42 -7.28 0.017 -3.36 -3.04 -3.14 -3.32 0.011 -17.36 -8.07 -7.88 -9.26 0.025 -1.57 -1.42 -1.45 -1.53 0.008 -11.62 -2.46 -2.52 -3.5 1 0.013 Without BSSE correction.With BSSE correction by the counterpoise method. MP2/6-31G** calculations. d RHF/6-31G** calculation. Chem. Commun., 1996 1633 Table 2H-H (A) distance, symmetry and structure of the complexes H H H-H-Y, X-H H-Y ?H H1 2 " 3 Structure System 6-31G** 6-31I++G** MP2/6-31G** Symmetry X Y ~~ BH4-...HCN 2.184 2.227 2.101 c3v 1 B CGN BH4-*.CH4 2.797 2.929 2.583 c3v 2B C LiH-NH4+ 1.390 1.39 1 -c3v 3 Li N LiH-HCN I .970 1.98 1 1.866 cmv LiH-HCCH 2.233 2.430 2.080 cmv BeH2-NH4+ 1.722 1.744 1.59 1 c3v 3 HBe N BeH2-HCN 2.248 2.306 2.1 15 cmv CH4**.NH4+ 2.237 2.357 2.226 c31' 2C N 8 T.B. Richarson, S. de Gala, R. H. Crabtree and P. E. M. Siegbahn, J.Am. Chem. SOC.,1995,117, 12875; E. Peris, J. C. Lee, J. E. Rambo, 0. Eisenstein and R. H. Crabtree, J. Am. Chern. Soc., 1995, 117, 3485. 9 E. S. Shubina, N. V. Belkova, A. N. Krylov, E. V. Vorontsov, L. M. Epstein, D. G. Gusev, M. Niedermann and H. Berke, J.Am. Chem. SOC.,1996, 118, 1105. 10 F. H. Allen, J. E. Davies, J. J. Galloy, 0. Kennard, C. F. Macrae, E. M. Mitchell, J. F. Mitchell, J. M. Smith and D. G. Watson, J. Chem. Info. Comput. Sci., 1991, 31, 187.11 J. J. Novoa, M.-H. Whangbo and J. M. Williams, J. Chem. Phys., 1991, 94, 4835. 12 The Mulliken populations are a rough measure of the gas-phase acidities (in kcal mol-I at 298 K): 203.5 (N&+), 351.2 (HCN), 378.0 (C2H2), 390.9 (C~HS)and 408.6 (CH& AH = 505 (k32) -674 (k127) e, n = 5, r2 = 0.90 (gas-phase acidities: NH4+ from J. E. Szulejko and T. B. McMahon, J. Am. Chem. SOC.,1993, 115, 7839; neutral compounds from S. G. Lias, J. F. Liebman, R. D. Levin, S. A. Kafafi and S. E. Stern, NIST Standard Reference Database, Computerized Version 2.02, 1994). 13 Gaussian 92DFT, M. J. Frisch, G. W. Trucks, H. B. Schlegel, I \====/1 P. M. W. Gill, B. G. Johnson, M. W. Wong, J. B. Foresman, M. A. Robb, M. Head-Gordon, E.S. Replogle, R. Gomperts, J. L. Andres, Fig. 1Plot of v2pin H-Be-H-.H-N+-H3 K. Raghavachari, J. S. Binkley, C. Gonzaez, R. L. Martin, D. J. Fox, D. J. Defrees, J. Baker, J. J. P. Stewart and J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1993. 14 Gaussian 94, M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, H.-*H-C, H..*H 1.91 A; A1-H***H143", H*-*H-C 155O, Al-H-sH-C torsion 95" (TEAMAL, tetraethylammonium B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Peterson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G.tetrahydroaluminate). Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala,An additional proof of the reliability of our calculations is W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts,provided by the AH value of the equilibrium NH4+ + CH4 R.L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker,[NH4CH4]+ in the gas phase: experimental value 3.59 f0.1 1,22 J. P. Stewart, M. Head-Gordon, C. Gonzilez and J. A. Pople, Gaussian, calculated value 3.51 kcal mol- l (Table 1). Inc., Pittsburgh PA, 1995. Thanks are given to the EU for the network 'Localization and 15 P. C. Hariharan and J. A. Pople, Theor. Chim. Acta, 1973,28,213. Transfer of Hydrogen' (No. CHRX CT 940582). We are 16 R.Krishnam, J. S. Binkley, R. Seeger and J. A. Pople, J. Chem. Phys., 1984,80, 3265. grateful to Drs J. L. Abboud, M. Alcami, 0.M6 and M. Yiiiez 17 C. Moller and M. S. Plesset, Phys. Rev., 1934, 46, 618. for fruitful discussions and useful information. I8 S.B. Boys and F. Bernardi, Mol. Phys., 1970, 19, 553. References 19 R. F. W. Bader, Atoms in Molecules. A Quantum Theory, Oxford University Press, New York, 1990. 1 M. D. Joesten and L. J. Schaad, Hydrogen Bonding, Marcel Dekker, 20 F. W. Bieger-Konig, R. F. W. Bader and T. H. Tang, J. Comput. Chem., New York, 1974; J. C. MacDonald and G. M. Whitesides, Chem. Rev., 1980,27, 1924. 1994,94,2383. 21 The H3B--H-H-N+H3 situation is not stable, when the structure is Perkin Trans. 2, 1995, 1315. minimized it evolves to H3B + NH3 + H-H which correspond to a well 2 T. Steiner, J. Chem. SOC., 3 T. Steiner, E. B. Starikov, A. M. Amada and J. J. C. Teixeira-Dias, known chemical reaction (N%Cl + LiBH4 -+ H3B-NH3 + LiCl + H2 J. Chem. SOC.,Perkin Trans. 2, 1995, 1321. (N. N. Greenwood and A. Earnshaw, Chemistry of the Elements, 4 I. Alkorta and S. Maluendes, J. Phys. Chem., 1995, 99, 6457. Pergamon, Oxford, 1984, 237). 5 R. Taylor and 0. Kennard, J. Am. Chem. Soc., 1982,104,5063. 22 S. L. Benet and F. H. Field, J.Am. Chem. SOC., 1972, 94, 5188, 6305. 6 L. Shimoni, H. L. Carell, J. P. Glusker and M. M. Coombs, J. Am. Chem. These authors propose that [NH&&]+ is a dimer with a structure 2 but SOC.,1994, 116, 8162. with X = N and Y = C which is not a minimum in our calculations. 7 J. A. Platts, S. T. Howard and K. Wozniak, Chem. Commun., 1996, 63. Received, 18th April 1996; Corn. 61027996 1634 Chem. Commun., 1996
ISSN:1359-7345
DOI:10.1039/CC9960001633
出版商:RSC
年代:1996
数据来源: RSC