X-ray charge density reveals fine details in π-stacks of semiquinone radicals which determine conductivity Krešimir Molčanov, Christian Jelsch, Ana Šantić, Vladimir Stilinović, Emmanuel Wenger, Biserka Kojić-Prodić

25th Slo-Cro Crystallographic Meeting, Ljubljana, june 2017. photo by N. Bedeković

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

Two polymorphs of N-MePy∙Cl4Q triclinic orthorhombic a b c b a c Molčanov, Stilinović, Šantić, Maltar-Strmečki, Pajić, Kojić-Prodić, Cryst. Growth Des., 2016, 16, 4777-4782.

N-MePy·Cl4Q, triclinic 2.903(1) Å 3.663(1) Å Peierls-type deformation Dimers with coupled spins Diamagnetic 2.903(1) Å Cryst. Growth Des., 2016, 16, 4777-4782.

Interactions between the rings (diamagnet, dimer) 2.90 Å Offset: 2.07 Å 0.5 e Å-3

Interactions between the rings (diamagnet, between dimers) 3.66 Å Offset: 2.8 Å 0.5 e Å-3

Critical points (diamagnet) ρmax > 0.095 e Å-3 2.90 Å ρmax < 0.040 e Å-3 3.66 Å (3, -1) bond (3, +1) ring cenroid (3, +3) cage centroid

N-MePy·Cl4Q, orthorhombic 3.283(1) Å 1D antiferromagnetic coupling in a stack Semiconductor: σ ≈ 10-6 ( cm)-1 EDC ≈ 0.34 eV 3.283(1) Å 3.283(1) Å Cryst. Growth Des., 2016, 16, 4777-4782.

Interactions between the rings (antiferromagnet) 3.28 Å Offset: 2.06 Å 0.5 e Å-3

Critical points (antiferromagnet) ρmax < 0.050 e Å-3 3.28 Å (3, -1) bond (3, +1) ring cenroid (3, +3) cage centroid

Stacking geometry: dimer vs. equdistant stack equidistant 2.90 Å 3.28 Å Offset: 2.07 Å Offset: 2.06 Å

Conductivity? e- e- e- e- e- Semiconductor Isolator huge ΔE 2.90 Å 3.28 Å e- huge ΔE 3.66 Å 3.28 Å e- e- 2.90 Å 3.28 Å ΔE = 0.34 eV

Electric conductivity vs. interplanar distance (100 K) Cl4Q∙N-MePy Br4Q∙N-MePy DDQ∙N-Me2Pic 3.2855(16) Å 3.1587(13) Å 3.122(3) Å

Inductive effect of the substituents Br4Q Cl4Q DDQ LUMO LUMO LUMO ΔE ΔE ΔE HOMO HOMO HOMO

[N-Me-4-(Me)2NPy]2(Cl4Q)3 A charge-transfer complex 2.84 Å 2.84 Å 1.32 Å 3.59 Å ≈1.76 Å

[N-Me-4-(Me)2NPy]2(Cl4Q)3 A charge-transfer complex –0,58 Charges derived from Pval: +0.96 –0,76 –1.92 –0,58 +0.96 2– 1+ 1+

Interactions between the rings ρmax < 0.045 e Å-3 3.59 Å 2.84 Å ρmax > 0.077 e Å-3

Conclusions energy of interaction exceeds 15 kcal mol-1 dominant interaction is spin coupling (interplanar distance) secondary: electrostatic (offset) possible electron transfer between the rings: semiconductivity magnetic properties can be tuned by tuning geometry of stacking

Thank you for your attention! Acknowlegdements Thank you for your attention! RBI, Zagreb Marijana Jurić Lidija Androš Dubraja Nadica Maltar-Strmečki Dijana Žilić Valentina Milašinović Lidija Kanižaj University of Zagreb Damir Pajić Nikolina Novosel Krešo Zadro KI, Ljubljana Jernej Stare Gregor Mali Jože Grdadolnik Rigaku Oxford Diffraction Ltd. Marcus Winter Dyanne Cruikshank Université de Lorraine Claude Lecomte Croatian Science Foundation, grant no. IP-2014-09-4079 Croatian Academy of Sciences and Arts French-Croatian bilateral, Slovenian-Croatian bilateral