1. Pradeep R. Varadwaj*, Arpita Varadwaj, Gilles H. Peslherbe A Computational Investigation of c-C 3 H 2  HX (X = F, Cl, Br) H-bonded Complexes Department of Chemistry & Biochemistry, Concordia University, 7141 Sherbrooke Street West, Montréal, Québec, Canada, H4B 1R6 *Email: pradeep@cermm.concordia.ca 66 th OHIO STATE UNIVERSITY INTERNATIONAL SYMPOSIUM ON MOLECULAR SPECTROSCOPY June 20-24, 2011 FB03

2. Hydrogen Bonding: A Versatile Interaction Contributing factors: To stabilize a hydrogen bond  Electrostatic  Short-range exchange  Polarization  Induction  Charge transfer  Dispersion (London type) A-X  H-Y N  H-O, N  H-N, O  H-O, O  H-N, C  H-O, C  H-N, O  H-C, N  H-C X, Y = electronegative atoms

3. Possible Potential Energy Surfaces of H-bond assisted systems Asymmetric double-well potential Symmetric double-well potential Low-barrier H-bond potential Single-well potential O…H-O H-atom is attached more strongly to O (covalently bonded) High barrier to H-atom transfer C. L. Perrin et al, Annu. Rev. Phys. Chem. 48 (1997) 511 - 44 C. L. Perrin, Science 266 (1994) 1665 – 1668; ACC. Chem. Res. 43 (2010) 1550-1557 H-atom is delocalized across a wide region Proton resides at the center

4. Interest & Motivation Fragments Cyclic – C 3 H 2 HX (X = F, Cl, Br) c-C 3 H 2 is a very important carbene of significant astrophysical interest, and it has found significant application in synthetic chemistry as well in transition metal catalysis and organic catalysis c-C 3 H 2  HX (X = F, Cl, Br) We are interested in examining  The efficiency of c-C 3 H 2 (i) as a proton donor, and (ii) as a proton acceptor  The singlet state (it is the most stable form which is feasible experimentally)  The potential energy surface (relaxed and rigid) to find the global minimum  The effect of an inappropriate basis set and of correlated functionals in the study of H-bonding  The amount of proton transfer (if any) and related signatures in identifying the existence of H-bonding in these complexes.

5. c-C 3 H 2  HF complex 0.88 Input to Gaussian 2.07 0.9649 Å 1.7613 Å Output from Gaussian B3LYP/aug-cc-pVTZ results  = 7.008 Isolated molecules  = 1.182 0.9241 Å  = 1.71 D  = 3.416 3198 2031 4072 111 Free Complex 874 cm -1 1920 km mol -1 Vibrational Properties

6. To locate the global minimum of c-C 3 H 2  HF complex in conjunction with four different basis sets, cc-pVDZ, cc-pVTZ, and their augmented analogues aug-cc- pVDZ and aug-cc-PVTZ. The plots are drawn between the scan ordinate  C– H  F (in degrees) and total electronic energy (in kcal mol -1 ). MP2 level relaxed potential energy surface scan 2.1 kcal

7.  MP2/aug-cc-pVQZ level equilibrium configurations of c-C 3 H 2  HX complexes  i), ii), and iii) represent complexes containing HF, HCl and HBr, respectively.  (a) the charge transfer (  Q/e) from the carbene lone pair electrons to the anti-bonding orbital  *(HX) and, the direction of  Q is shown by an arrow in blue. Each upper and lower line entries in (b) and (c) represents the value of charge (or  Q) obtained from Bader- and natural population analysis schemes, respectively.  (b) The Bader and NPA based atomic charges given for selected atoms (involved in H-bond formation) as in the complexes – An indication of charge rearrangement on H-bond formation.  (c) the inter-molecular and halogen halide bond distances (in Å ).

8. Complex typeBasis  EbEb E b zpe rr c-C 3 H 2  HF MP2/ACCT1.562-13.5011.240.8256 MP2/ACCQ1.546-13.3411.140.8320 PBE0/ACCQ1.699-14.2412.090.7795 B3LYP/ACCQ1.738-13.5411.400.7978 B3LYP-D/ ACCQ1.702-13.5311.370.7963 c-C 3 H 2  HCl MP2/ACCT2.223-10.128.560.5047 MP2/ACCQ2.260-10.068.570.4930 PBE0/ACCQ2.894-10.699.300.3460 B3LYP/ACCQ2.574-9.137.670.4580 B3LYP-D/ ACCQ2.608-9.127.650.4344 c-C 3 H 2  HBr MP2/ACCT2.941-10.278.820.2705 MP2/ACCQ3.372-10.539.420.1710 PBE0/ACCQ7.169-11.469.89-0.5354 B3LYP/ACCQ3.924-8.527.630.0922 B3LYP-D/ ACCQ7.703-9.367.40-0.6458 Some Selected Computed Properties

9. Illustration of the 1D-motion of the oscillating proton along the line between the carbenic C and the heavy-atom X (X = F, Cl, Br) with a fixed separation of the heavy atom C  X bond distance at the equilibrium geometry of each c-C 3 H 2  HX complex. The motion is described approximately by an asymmetric single- (X = F) and double-well (X = Cl, Br) potential functions. MP2/aug-cc-pVTZ rigid-potential energy surface Scan

10. ComplexE es E ex E pl E ct E es +E ex +E pl +E ct EE BSSE  E (BSS E) c-C 3 H 2  HF -22.3421.7-6.50-4.03-11.19-11.68-0.04 - 11.65 c-C 3 H 2  HCl -20.6028.4-7.60-5.73-5.54-5.98-0.01-5.97 c-C 3 H 2  HBr -27.5447.6 - 14.72-9.84-4.52-4.98-0.02-4.96 RHF/aug-cc-pVQZ decomposed energy components (kcal mol-1) obtained from the RMP2/aug-cc-pVQZ equilibrium geometries of the c-C3H­2  HX (X = F, Cl, and Br) complexes at the RVS-SCF level

11. Quantum Theory of Atoms in Molecules (QTAIM) Analysis  b > 0 but small  2  b > 0 H b > 0 Non-covalent interaction  b >> 0  2  b < 0 H b < 0 Covalent interaction  b > 0 but small  2  b > 0 H b < 0 Mixed interaction: both ionic and covalent components

12. c-C 3 H 2 … HF Bond type bb 1 2 3  2  b bb VbVb GbGb |V b |/G b HbHb DI C1 C20.2942-0.5611-0.37570.3295-0.60730.4935-0.48750.16792.9044-0.31971.0919 C2 H60.0479-0.0778-0.07760.21560.06020.0025-0.03960.02731.4497-0.01230.1107 H6 F70.3254-2.2856 0.9160-3.65510.0000-1.11310.099711.1675-1.01350.3058 RCP C1 C2 C30.2604-0.39640.27080.28390.1583-0.48500.26231.8491-0.2227 c-C 3 H 2 … HCl C1 C20.2933-0.5584-0.37270.3295-0.60160.4985-0.48560.16762.8974-0.31801.0887 C2 H60.0461-0.0694-0.06920.19300.05430.0023-0.03390.02371.4275-0.01010.1614 H6 Cl70.2233-0.6078-0.60760.3765-0.83880.0003-0.31600.05325.9435-0.26290.6333 RCP C1 C2 C30.2599-0.39620.27060.28170.1561-0.48330.26121.8506-0.2221 c-C 3 H 2 … HBr C1 C20.2980-0.5687-0.38440.3298-0.62330.4795-0.49800.17112.9108-0.32691.0929 C2 H60.0673-0.1174-0.11710.26130.02680.0031-0.05400.03031.7791-0.02360.2239 H6 Br70.1696-0.3507-0.35040.2960-0.40520.0009-0.19150.04514.2468-0.14640.6392 RCP C1 C2 C30.2632-0.40060.27430.28730.1610-0.49450.26741.8495-0.2271 c-C 3 H 2 C2 C10.2897-0.5572-0.35260.3246-0.58520.5802-0.48170.16772.8724-0.31401.0814 C1 C30.3354-0.6096-0.51190.3098-0.81160.1909-0.60730.20223.0035-0.40511.3800 RCP C1 C2 C30.2600-0.40570.26490.27170.1309-0.47940.25601.8722-0.2233 HF H - F0.3766-2.8261 1.0377-4.61450.0000-1.34680.096613.9454-1.25020.3923 HCl H - Cl0.2577-0.6676 0.3728-0.96240.0000-0.37180.06565.6678-0.30620.8633 HBr H - Br0.2110-0.4087 0.3148-0.50270.0000-0.27370.07403.6983-0.19970.9624 QTAIM topological properties of c-C 3 H 2  HX (X = F, Cl, and Br) complexes obtained from the MP2/aug-cc-pVQZ level of theory.

13. Summary Disappointing performance of the use of small double-zeta basis sets which provide less, inaccurate, and inappropriate results so that a serious conclusion can be easily derived for any weakly bound chemical system. Therefore, it is wise to use at least a triple zeta quality basis set with at least one d- polarization function to describe the reactive intermediates (transition states) following a reactive path in a chemical reaction. The studied complexes are all red-shifted H-bonded systems. There will be one and only one minimum – the so-called global minimum – on the PES; the F-end of HX will not form any complex with H-end of c-C 3 H 2. The red-shift of the HX vibrational frequency, with concomitant bond elongation, appearance of bond paths connecting the nuclei of bonded atoms with some amount of electron density at bcps and the charge transfer effect etc. provide signature of H- bonding. It is found that c-C 3 H 2 is a strong hydrogen bond acceptor than a H-bond donor. A future experimental set up on these systems might lead to more conclusive remarks. Acknowledgements Arpita Varadwaj Gilles H. Peslherbe PBEEE Merit Postdoctoral Scholarship Award Committee, Quebec, Canada Japan Society for the Promotion of Science & Osaka Supercomputing Facilities, Japan

14. Conventional Signatures of Hydrogen bonding  Enhancement of dipole moment of the complex  Electron transfer from a bonding orbital of electron donor atom or group (HOMO) to the anti-bonding orbital (LUMO) of the proton donor group  Lengthening of the HY bond, with this, there is an accompanying red-shift of the HY normal mode vibration  H-bond distance < sum of van der Waals radii of non- bonded atoms ???? G. R. Desiraju, Angew Chem. Int. Ed. 50, 2011, 52 – 59

15. N = 1.55 Å O = 1.52 Å H = 1.05 to 1.20 Å