Probing Halogen Bonds with NMR One- and
Two-Bond Spin-Spin Coupling Constants
Halogen bonds:
1J(F-Cl)
19F-35Cl…15N
1XJ(Cl-N)
Janet E. Del Bene
2XJ(F-N)
Methods for structure optimization and the
calculation of spin-spin coupling constants
1. Structure optimization: (Gaussian 03)
F-Cl…N:
MP2/aug’-cc-pVTZ
2. Coupling constants:
a. Method: Equation-of-motion coupled cluster singles and
doubles (EOM-CCSD) (ACES II)
b. Basis set: Ahlrichs (qzp,qz2p)
c. J Terms: paramagnetic spin-orbit (PSO), diamagnetic
orbit (DSO), Fermi contact (FC), and spin dipole (SD)
spin-
Cl-N distances (Å) and binding energies (kcal/mol) for
complexes with F-Cl…N halogen bonds
Legon (gas-phase)a
MP2/aug’-cc-pVTZ
Complex
Ro(Cl-N), Å
Re(Cl-N)
FCl…NCH
2.69
2.54
5.8
FCl…NC-CH3
2.56
2.47
7.1
FCl…NH3
2.37 (“little ion-pair”)
2.24
11.7
FCl…N(CH3)3
2.09 (“70% ion-pair”)
2.04
23.9
ΔEe
a) A. C. Legon, “The interaction of dihalogens and hydrogen halides
with Lewis bases in the gas-phase” Struct. Bond. (2008) 126, 17.
Binding energies for complexes with halogen bonds vs.
binding energies for complexes with hydrogen bonds
ΔEX (kcal/mol)
25
20
15
10
5
0
0
5
10
ΔEH (kcal/mol)
15
20
F-Cl…N halogen-bonded complexes
Nitrogen bases
sp2
sp3
N≡N
Z-HN=NH
NH2F
F-C≡N
H2C=NH
NH3
sp
H-C≡N
NH(CH2)2 cyc
H3C-C≡N
NH2(CH3)
Li-C≡N
R(F-N) and R(F-Cl) vs. R(Cl-N) (Å) in complexes
with F-Cl…N halogen bonds
4.5
1.8
4.4
1.76
4.2
1.72
4.1
1.68
4
3.9
1.64
3.8
← R(F-N)
R(F-Cl) →
3.7
1.6
2
Strong base
2.1
2.2
2.3
2.4
2.5
R(Cl-N), Å
2.6
2.7
2.8
2.9
Weak base
Å
Å
4.3
2hJ(F-N)
vs. R(F-N) for complexes
with F-H…N hydrogen bonds
-80
R2 = 0.97
2hJ(F-N),
Hz
-60
-40
-20
0
2.5
2.6
2.7
2.8
R(F-N), Å
2.9
3.0
3.1
2XJ(F-N)
and 1XJ(Cl-N) vs. the F-N
distance for F-Cl…N halogen bonds
-90
2XJ(F-N);
R2 = 0.99
1XJ(Cl-N);
R2 = 0.95
-80
-70
Hz
-60
-50
-40
-30
-20
-10
0
_________________
│
│
│
│
│
3.8
3.9
4
4.1
R(F-N), Å
4.2
4.3
4.4
4.5
1J(F-Cl)
as a function of the F-Cl distance (Å)
for complexes with F-Cl…N halogen bonds
Monomer
800
R2 = 0.93
1J(F-Cl),
Hz
780
760
740
NCLi
720
700
NH2F
680
Z-N2H2
660
1.62
1.64
1.66
1.68
1.7
R(F-Cl), Å
1.72
1.74
1.76
Across the proton-transfer coordinate for F-H…NH3
2hJ(F-N)
450
→
-70
-60
350
-50
250
Hz
150
←
1hJ(H-N)
1J(F-H)
→
-30
-20
50
-10
-50
0
-150
0.95
1.05
1.15
1.25
R(F-H), Å
1.35
1.45
10
1.55
Hz
-40
Across the Cl-transfer coordinate for F-Cl…NH3
700
-120
680
-100
← 1J(F-Cl)
2XJ(F-N)
→
660
-80
Hz
Hz
640
1XJ(Cl-N)
-60
→
620
-40
600
-20
580
0
2.3
2.2
2.1
2
R(Cl-N), Å
1.9
1.8
1.7
Why doesn’t 1XJ(Cl-N) in the complex approach
1J(Cl-N)
in the isolated ion?
F-……+Cl-NH3
-31 Hz
Complex:
Ion:
+Cl-NH
3
+9 Hz
F(-0.41e) Cl(+0.25e) N(-0.49e)
Cl(+0.32e) N(-0.04e)
Conclusions
1. Coupling constants across halogen bonds can be used to
characterize complexes with F-Cl…N halogen bonds. Both
2hJ(F-N) for hydrogen bonds and 2XJ(F-N) for halogen bonds
increase in absolute value with decreasing F-N distance.
2. Changes in coupling constants along the Cl transfer are quite
different from changes in corresponding coupling
constants across the proton-transfer coordinate.
3. Complexes of F-Cl with the stronger N bases are more stable
than corresponding complexes of F-H, and should be
amenable to experimental investigations of coupling
constants at low temperatures.
Acknowledgments
José Elguero and Ibon Alkorta, CSIC, Madrid
US National Science Foundation CHE-9873815
Ohio Supercomputer Center
Congratulations, Russ Pitzer, on a long and
productive scientific career
as a University Professor teacher and researcher in quantum chemistry.
Wishing you continued success and enjoyment!
EOM-CCSD and SOPPA (Second-order Polarization
Propagator Approximation) vs. Experimental 1J(X-Y), Hz
700
HmX-YHn and F-substituted derivatives
500
300
100
-700.00
-500.00
-300.00
-100.00
-100
100.00
300.00
500.00
700.00
-300
-500
J(exp) = 1.007J(EOM) – 2.123
R2 = 0.997
J(exp) = 1.201J(SOP) – 17.48
R2 = 0.962
Del Bene, Alkorta, Elguero, JCTC,
2008, 4, 967.
-700