1. Daniel Zaleski,a John Mullaney,a Nicholas Walkera and Anthony Legonb
Formation of Complexes CyclopropaneMCl (M = Ag or Cu) and their Characterization by Broadband Rotational Spectroscopy
70th International Symposium on Molecular Spectroscopy,
University of Illinois, Champaign-Urbana, June 2015
Daniel Zaleski,a John Mullaney,a Nicholas Walkera and Anthony Legonb
aSchool of Chemistry, University of Newcastle
bSchool of Chemistry, University of Bristol

2. Background: Involvement of π electrons in hydrogen-bond interactions
→ Rules for angular geometry
in hydrogen-bonded complexes
π-electrons
in ethyne
Hydrogen bond
to  electrons
π-electrons
in ethene
Hydrogen bond
to  electrons
A. C. Legon, P. D. Aldrich and W. H. Flygare,
J. Chem. Phys., 75, , (1981).
P. D. Aldrich, A. C. Legon and W. H. Flygare,
J. Chem. Phys., 75, , (1981)

3. Background: Involvement of π electrons in halogen-bond interactions
→ Rules for angular geometry
in halogen-bonded complexes
π-electrons
in ethene
Halogen bond
to  electrons
Halogen bond
to  electrons
π-electrons
in ethyne
H.I. Bloemink, J.H. Holloway and A.C. Legon,
Chem. Phys. Letters, 250, , (1996).
K. Hinds, J.H. Holloway and A.C. Legon, J. Chem. Soc.
Faraday Trans., 92, , (1996).

4. More recent background: Systematic investigations of complexes of
Lewis bases with CuX and AgX
S. L. Stephens, D. M. Bittner, V. A. Mikhailov, W. Mizukami, D. P. Tew,
N. R. Walker and A. C. Legon, Inorg. Chem., 53, , (2014).
S. L. Stephens, D. P. Tew, V. A. Mikhailov, N. R. Walker
and A. C. Legon, J. Chem. Phys., 135, , (2011).
CuCl and AgCl also undergo non-covalent interactions with π system of ethene,
but note distortion of ethene. Angular geometries of C2H4HCl, C2H4ClF
and C2H4Cu Cl and C2H4AgCl are isomorphic

5. More recent background: Systematic investigations of complexes of Lewis bases with CuCl and AgCl
S. L. Stephens, D. M. Bittner, V. A. Mikhailov, W. Mizukami, D. P. Tew,
N. R. Walker and A. C. Legon, Inorg. Chem., 53, , (2014).
S. L. Stephens, W Mizukami, D. P. Tew, N. R. Walker
and A. C. Legon, J. Chem. Phys., 137, , (2012).
Non-covalent interactions with CuCl and AgCl are strong enough to lengthen
C≡C by ≈0.02 Å and increase HCC angle by several degrees. Angular geometries
of C2H2HCl, C2H2ClF and C2H2Cu Cl and C2H2AgCl are isomorphic

6. → Pseudo-π character of cyclopropane
Coulson-Moffitt model of cyclopropane →
sp3 hybridization of C, overlap of
lobes on adjacent C atoms
‘bent’ bond of a pseudo-π type.
Pseudo- complexes of cyclopropane with CuCl or AgCl?

7. How to synthesize molecules BMCl inside
a Pate-type broadband FTMW spectrometer

8. Broadband rotational spectrum of cyclopropane with CuCl
Upward pointing: Observed
Down pointing: Simulated
(PGOPHER)
Blue: c-C3H6 -63 Cu-35Cl
Red: c-C3H6-65Cu-35Cl
Note: ‘fuzz’ is nuclear quadrupole
hfs arising from two quadrupolar
nuclei (63,65Cu,35Cl)

9. Broadband rotational spectrum of cyclopropane with AgCl
Upward pointing: Observed
Down pointing: Simulated
(PGOPHER)
Blue: c-C3H6- 107Ag-35Cl
Red: c-C3H6 -109Ag-35Cl
Note: less ‘fuzz’ because only
one quadrupolar nucleus (35Cl)

10. Ground-state spectroscopic constants of naturally abundant isotopologues
A0/MHz
B0/MHz
C0/MHz
ΔJ/kHz
ΔJK/kHz
χaa(Cl)/MHz
χaa(Cu)/MHz
c-C3H6-63Cu-35Cl
18059(17)
(43)
(42)
0.1329(51)
2.40(17)
(69)
57.307(85)
c-C3H6-65Cu-35Cl
18058(19)
(40)
(52)
[0.1329]
[2.40]
-24.50(16)
52.97(22)
c-C3H6-107Ag-35Cl
(10)
(39)
(41)
0.0991(23)
3.665(92)
-31.26(26) …
c-C3H6-109Ag-35Cl
(38)
(32)
(30)
[0.0991]
[3.665]
-31.18(26)
Pa/(u Å2)
Pb/(u Å2)
Pc/(u Å2)
(13)
22.884(13)
5.101(13)
(15)
22.885(15)
5.101(15)
(15)
(15)
(15)
(12)
(12)
5.1879(12) N
σRMS/kHz 91
10.8 32
10.7 34
10.3 33
9.4

11. Isotopologues investigated
c-C2H4CD2-63,65Cu-35Cl (CD2 off a-axis)
c-C3H6-63,65Cu-35Cl
c-CD2C2H4-63,65Cu-35Cl ( CD2 on a-axis)
c-C2H4CD2-63Cu-37Cl (CD2 off a-axis)
c-C3H6-63Cu-37Cl
(8 isotopologues)
cyclopropaneCuCl
c-C3H6-107,109Ag-35Cl
c-C3H6-107,109Ag-37Cl
c-CD2C2H4-107,109Ag-35Cl ( CD2 on a-axis)
c-C2H4CD2-107,109Ag-35Cl (CD2 off a-axis)
(8 isotopologues)
cyclopropaneAgCl
A0 independent of Cu or Cl isotope
A0 independent of Ag or Cl isotope

12. Planar moments are revealing!
Mean Pc for H containing isotopologues:
c-C3H6-AgCl = (10) u Å2
c-C3H6-CuCl = 5.101(15) u Å2
c-C3H = (6) u Å2
Mean Pb for H containing isotopologues:
c-C3H6-AgCl = (5) u Å2
c-C3H6-CuCl = (15) u Å2
c-C3H = (6) u Å2
Substantial increases in bC and bH and in r (C-C)Front

13. * Geometry of cyclopropaneAgCl rside(C−C) = 1.486(8) Å (1.5016 Å)
57.7(2)⁰ *
rfront(C−C) = (17) Å
( Å)
Numbers in black: r0 geometry
fitted with STRFIT (Z. Kisiel).
(in brown: CCSD(T)/cc-pVTZ)
r(*Ag) = (53) Å
( Å)
r(Ag−Cl) = (47) Å
( Å)

14. Do pseudo-π bonds also be acceptors for hydrogen/halogen bonds?
A. C. Legon, P. D. Aldrich and W. H. Flygare,
J. Amer. Chem. Soc., 104, , (1982).
K. Hinds, J.H. Holloway and A.C. Legon,
J. Chem. Soc. Faraday Trans., 93, , (1997).
CyclopropaneMCl: non-covalent bond to pseudo-π electrons
CyclopropaneHCl:
Hydrogen bond to
pseudo-π electrons
CyclopropaneClF:
Halogen bond to
pseudo-π electrons

15. Distortions δr0(CC) of π- and pseudo-π bonds on non-covalent interaction with CuCl (relative to free Lewis base)
δr(C≡C) = (25)Å
δr(C=C) = (44) Å
δrfront (C−C) = (9)Å
δrside (C−C) = (4)Å

16. with AgCl (relative to free Lewis base)
Distortions δr0 (CC) of π- and pseudo-π bonds on non-covalent interaction
with AgCl (relative to free Lewis base)
δr(C≡C) = (22) Å
δr(C=C) = (18) Å
δrfront (C−C) = (17)Å
δrside (C−C) = (8)Å

17. Why does cyclopropane suffer greater distortion than ethyne or ethene?
Are the cyclopropaneMCl complexes more strongly bound?
BMCl
Dissociation energy,*
De/kJ mol-1
CC bond distortion
δr0(CC)/Å
C2H2CuCl
148
0.0268(25)
C2H4CuCl
155
0.0284(44)
c-C3H6CuCl
105
0.1027(9)
C2H2AgCl 98
0.0165(22)
C2H4AgCl 94
0.0132(18)
c-C3H6AgCl 66
0.0733(17)
* Ab initio, CCSD(T)/cc-pVTZ (or better), bsse corrected

18. Why are the CC bond distortions larger in cyclopropane?
Ethyne
Ethene
Cyclopropane
Two  + one σ CC bond
One  + one σ CC bond
Only a pseudo- CC (single) bond

19. Conclusions
Pseudo-π bond of cyclopropane undergoes non-covalent interaction with hydrogen-bond donors,
halogen-bond donors and ‘metal’-bond donors.
Geometries of hydrogen-bonded, halogen-bonded and ‘metal’-bonded complexes with
cyclopropane are isomorphic. Also for ethyne and ethene series.
EthyneMCl, etheneMCl and cyclopropaneMCl all show CC bond lengthening on
complex formation, but much larger for cyclopropane as Lewis base.

20. Geometry of cyclopropaneCuCl
rside(C−C) = 1.468(4) Å
( Å)
56.5(1)⁰ *
rfront(C−C) = (9) Å
( Å)
Numbers in black: r0 geometry
fitted with STRFIT (Z. Kisiel).
in brown: CCSD(T)/ccpVTZ)
r(*Cu) = (46) Å
( Å)
r(Cu−Cl) = (41) Å
( Å)