1. Iodide∙∙∙π interactions of perhalogenated quinones in co-crystals with organic bases
Krešimir Molčanov, Vladimir Stilinović, Gregor Mali, Jože Grdadolnik, Jernej Stare, Valentina Milašinović, Biserka Kojić-Prodić

2. Quinone / hydroquinone system
Semiquinone radical
Quinone
Semiquinone
radical anion
Hydroquinone

3. Semiquinone radicals .. X = Cl : Cl4Q X = Br : Br4Q X = Cl, CN : DDQ
X = F :
F4Q

4. Three types of semiquinone stacks: N-MePy·Cl4Q, [N-Me-4-(Me)2NPy]2(Cl4Q)3
dimers
equidistant radicals
trimers
2.84 Å
2.86 Å
3.17 Å
3.60 Å
3.59 Å B A
diamagnetic,
insulator
antiferromagnetic,
semiconductor
Cryst. Growth Des., 2016, 16,
Chem. Eur. J., 2018, 24,
diamagnetic,
insulator

5. …
Emprical formula:
C6Cl4O2Na

6. Preparation
Quinone
Iodide salt
Semiquinone radical
salt

7. Obtained by serendipity: co-crystals of organic iodide salts with quinones

8. The main motives

9. Geometric parameters
d(Cg)
d(plane)

10. Anion∙∙∙π interactions?
electrostatic potential
Voronoi-Dirichlet
polyhedra

11. Lone pair···π interaction (π-hole, n→π*)?
Cl4Q-
anion radical
Cl4Q

12. Partial charge transfer?
Br4Q
70 – 80°
3.54 – 3.94 Å
offset ≈ 1 Å
N-Me-2-pic∙I∙Br4Q

13. Charge transfer: molecular geometry
elongated
shortened
elongated

14. Charge transfer: IR and solid-state NMR spectra
more shielded:
significant upfield shift
red shift
blue shift
slight upfield
shift
red shift

15. Charge transfer: DFT calculations
-0.60 ─ -0.65
0.28 – 0.40 e-
-0.28 ─ -0.40
Probable degree of
charge transfer:
≤ 0.05 e-
Charge of the cation:
+0.77 ─ +0.82

16. New systems with divalent cations+ + + +

17. Conclusions & outlook A novel type of anion···π interaction
Much stronger than known anion···π and lone-pair···π interactions
Charge transfer between iodide anion and the quinoid ring (ca e-), overestimated by DFT
„Arrested” reduction of the quinone into a semiquinone radical anion
Further study: X-ray charge density, more elaborate quantum chemical study

18. Acknowlegdements Thank you for your attention!
Croatian Science Foundation, grant no. IP
Croatian Academy of Sciences and Arts, grants for 2013, 2014 and 2016
Slovenian-Croatian bilateral (2016 – 2017)