- and CH- interactions in the molecular nitrogen- and

methane-pyridine complexes

Department of ChemistryUniversity of Alberta

Valuable prototypes for the - and CH- interactions found in many reactive systems.

Supramolecular structures

DNA - stacking and assembly

CH- attraction in asymmetric hydrogenation reactions

MOTIVATION

a T. Steiner and G. R. Desiraju Chem. Commun. 8, 891 (1998).

b The CH/pi Interaction, by M. Nishio, M. Hirota, and Y. Umezawa (1998).

c M. Yamakawa, I. Yamada, R. Noyori, Angew. Chem. Int. Ed., 40, 15,2818 (2001).

What is CH- interaction?

A weak noncovalent bond occurring between soft acids and soft bases.

But is it a non-conventional weak hydrogen bond? a Is it more like ‘hydrogen bond’ C-H O?

b Fig.1

c Fig.2

Hydrogen bonds diagram: G. R. Desiraju, Acc. Chem. Res., 35, 565 -573, (2002).

a MATI: K. Shibasaki, A. Fujii, N. Mikami, and S. Tsuzuki, J. Phys. Chem. A 110, 4397 (2006).

WEAKLY BOUND

N2-C5H5N 1.3 Kcal/mol

a CH4-C6H6 1.1(1) Kcal/mol

Dispersion interaction

What are we doing?

15N2 - C5H5N CH4 - C5H5N

Answers to questions.

1. How do N2, CH4 interact with a polar aromatic nitrogen heterocycle?

2. What is the vdW bond distance?

-not well measured for CH4-C6H6

FTMW

MW EXPERIMENTAL RESULTS

15N2 - C5H5N

The spectrum of 15N2-C5H5N.

Sample: 0.5% pyridine + 2.5% 15N2 + 4 atm. Ne

A1 ( = 0, I = 0) state B2 ( = 1, I = 1) state MP2/6-311G(d,p)

A /MHz 2849.35719(31) 2850.30605(36) 2807.5641

B /MHz 1447.94807(22) 1447.93251(34) 1455.4888

C /MHz 1424.36088(22) 1424.37664(30) 1429.2876

1.5aa /MHz 4.9192(23) 4.9290(36)

0.25(bb-cc) /MHz 1.54038(83) 1.5393(11)

DJ /kHz 4.1478(44) 4.1791(71)

DJK /kHz 18.773(16) 18.721(21)

DK /kHz 22.761(40) 20.642(26)

d1 /kHz -0.0090(41) -0.0211(67)

d2 /kHz 0.0312(19) 0.0352(18)

Number of lines 164 134

RMS /kHz 3.8 4.7

The fit: 15N2-C5H5N

A1 ( = 0, I = 0) state B2 ( = 1, I = 1) state MP2 rigid dimer Pyridine

R /Å 3.47 3.47 3.46

/ 10(1) 10(1) 4.6

/ 90.0 90.0 90.0

V2 /cm-1 64.66 64.66

tor /cm-1 22.52 22.52

aa /MHz 3.2795(15) 3.2880(24) -4.908(3)

bb /MHz 1.4410(166) 1.4946(44) 1.434(3)

cc /MHz -4.72051(166) -4.7226(44) 3.474(3)

Ia /amu Å2 177.49055(31) 177.30693(36) 180.00622 83.6824(6)

Ib /amu Å2 349.03116(22) 349.03492(34) 347.22287 87.0606(6)

Ic /amu Å2 354.81106(22) 354.80714(30) 353.58804 170.7816(6)

N2-OCS V2 = 40 cm-1

J. P. Connelly, S. P. Duxon, S. K. Kennedy, B. J. Howard, and J. S. Muenter, J. Mol. Spectrosc. 175, 85-98 (1996).

Structural information: 15N2-C5H5N

The structure 15nitrogen-pyridine dimer.

MP2/6-311G(d,p) binding energy: 438 cm-1 (1.3 kcal/mol)

Dimer R/Å

C5H5N-N2 3.47aC6H6-N2 3.50

bC6H4F2-N2 3.48

c(N2)2 3.50

a Y. Ohshima, H. Kohguchi, and Y. Endo, Chem. Letts. 184, 21 (1991).

b Schäfer, C. Kang, and D. W. Pratt, J. Phys. Chem. A 107, 10753-10758 (2003).

C A. Wada and H. Kanamori, J. Chem. Phys. 109, 9434 (1998). [MP4 theory]

N-N-N interaction

MW EXPERIMENTAL RESULTS

CH4 - C5H5N

A floppy vdW system

Theory shows vdW bond distance can vary depending on the calculation methods.

a K. Shibasaki, A. Fujii, N. Mikami, and S. Tsuzuki, J. Phys. Chem. A 110, 4397 (2006).

The spectrum of CH4-C5H5N.

Sample: 0.5% pyridine + 2.5% CH4 + 3 atm. Ne

Constant Unit 12CH4-C5H5NA-state

(jCH4 = 0, ICH4 = 2)

12CH4-C5H5NF-state

(jCH4 = 1, ICH4 = 1)

13CH4-C5H5N

A MHz 3006.3471(24) 3007.0366(69) 3002.090(13)

B MHz 1873.8308(44) 1885.2402(83) 1820.3973(33)

C MHz 1829.4969(62) 1843.667(10) 1782.8535(33)

DJ kHz 109.67(10) 224.17(14) 177.32(19)

DJK kHz 32.9(36) -144.2(30) -772.1(32)

DK kHz 373.6(470) 101.2(40) 437.1(21)

d1 kHz - 86.21(17) 86.21

d2 kHz - -42.32(79) -42.32

RMS kHz 2.0 4.3 4.2

aa MHz 2.99(16)

bb MHz 3.92(31)

cc MHz 0.93(31)

Maa MHz 0.036(29)

RMS kHz 88.0 b-dipole transitions

The structure of methane-pyridine: A vdW complex

MP2/6-311++G(d,p) binding energy: 361 cm-1 (1.03 kcal/mol)

a M. Schauer and E. R. Bernstein, J. Chem.Phys. 82, 726 (1985).

b D. A. Roham, S. Suzuki, R. D. Suenram, F. J. Lovas S. Dasgupta, W. A. Goddard III, and B. A. Blake, Nature, 362, 735 (1993).

Dimer R/Å

C5H5N-CH4 3.77

a C6H6-CH4 3.4-3.5

b C6H6-NH3 3.59

A non-conventional NH hydrogen bond complex

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