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

Quinone / hydroquinone system Semiquinone radical Quinone Semiquinone radical anion Hydroquinone

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

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, 4777-4782. Chem. Eur. J., 2018, 24, 8292-8297. diamagnetic, insulator

… Emprical formula: C6Cl4O2Na

Preparation Quinone Iodide salt Semiquinone radical salt

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

The main motives

Geometric parameters d(Cg) d(plane)

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

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

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

Charge transfer: molecular geometry elongated shortened elongated

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

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

New systems with divalent cations + + + +

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. 0.05 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

Acknowlegdements Thank you for your attention! Croatian Science Foundation, grant no. IP-2014-09-4079 Croatian Academy of Sciences and Arts, grants for 2013, 2014 and 2016 Slovenian-Croatian bilateral (2016 – 2017)