The synthesis of four nitronyl nitroxide (NN) biradicals is described which are conjugatively linked through p-ter-phenyl (PPP), ter-thiophene (TTT) and alternating phenylene (P) and thiophene (T) units as PTP and TPT. We first utilized Suzuki and Stille coupling reactions through protection and deprotection protocols to synthesize these (NN) biradicals. Single crystals were efficiently grown for radical precursors of 3, 5, 6, PPP-NNSi, PTP-NNSi, and final biradicals of TTT-NN, TPT-NN, and PPP-NN, whose structures and molecular packing were examined by X-ray diffraction studies. As a result, much smaller torsions between the NN and thiophene units (∼10°) in TTT-NN and TPT-NN than for NN and phenyl units (∼29°) in PPP-NN were observed due to smaller hindrance for a five vs a six membered ring. All four biradicals TTT-NN, TPT-NN, PTP-NN, and PPP-NN were investigated by EPR and optical spectroscopy combined with DFT calculations. The magnetic susceptibility was studied by SQUID measurements for TTT-NN and TPT-NN. The intramolecular exchange interactions for TPT-NN and TTT-NN were found in good agreement with the ones calculated by broken symmetry DFT calculations.

In this paper, we describe the stereospecific synthesis and functional properties of C 2- and C 1-symmetric pyrene-fused [5]­helicene molecules 1 and 2 connected via hexagonal and heptagonal rings, respectively. Both molecules showed high configurational stability and distinct functional properties, which were attributed to the fusing mode of [5]­helicene with the pyrene and molecular symmetry. The estimated Gibbs activation energy for enantiomerization of 2 is one of the highest reported values for any π-conjugated molecules incorporating [5]­helicene moiety.

We have demonstrated that it is possible to evaporate diradicals in a controlled environment obtaining thin films in which the diradical character is preserved. However, evaporation represents a challenge. The presence of two radical sites makes the molecules more reactive, even in case of very stable single radicals. We have explored the parameters that play a role in this phenomenon. Bulk formation thermodynamics and delocalisation of the unpaired electrons play the major role. The higher the formation energies of the crystal, the more difficult is the evaporation of intact radicals. The larger the delocalization, the more stable is the film exposed

Four weakly antiferromagnetic interacting biradicals of benzo­[1,2-b:4,5-b′]­dithiophene (BDT) and BDT extended with two thiophenes (BDTTh2) linked with nitronyl and imino nitroxides (NN and IN) as BDT–NN, BDT–IN, BDTTh2–NN, and BDTTh2–IN were designed, synthesized, and characterized. Short intermolecular π–π distances were found (3.42 Å) for BDT–NN, whereas larger ones were found for BDT–IN (3.54 Å) and BDTTh2–NN (3.67 Å), respectively. Intramolecular magnetic interaction (J intra,exp/k B) of BDT–NN (−26 K) is much larger than for BDT–IN (−5.3 K), while it is reduced for the dithiophene-extended molecule BDTTh2–NN (−2.3 K). Intermolecular interactions (zJ inter,exp/k B) of BDT–NN (−6.5 K) and BDT–IN (−6.0 K) are stronger than for BDTTh2–NN (–4.6 K). Such large intermolecular couplings resulting from good π-stacking mark BDT-IN and BDTTh2–NN as promising crystalline materials with similar sized J intra and J inter. In addition, we also extracted a coupling within the chain of J chain/k B = −2.2 K and a coupling between the chains of zJ interchain = −1.5 K for BDTTh2–NN by a Heisenberg chain model. Intra- and intermolecular interactions and spin densities were examined by DFT studies.

Two stable nitronyl nitroxide free radicals { R 1 = 4′-methoxy-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (NNPhOMe) and R 2 = 2-(2′-thienyl)-4,4,5,5-tetramethylimidazoline 3-oxide 1-oxyl (NNT)} are successfully synthesized using Ullmann condensation. The reactions of these two radicals with 3d transition metal ions, in the form of M(hfac) 2 (where M = Co or Mn, hfac: hexafluoroacetylacetone), result in four metal–organic complexes Co(hfac) 2 (NNPhOMe) 2 , 1 ; Co(hfac) 2 (NNT) 2 ·(H 2 O), 2 ; Mn(hfac) 2 (NNPhOMe)· x (C 7 H 16 ), 3 ; and Mn(hfac) 2 (NNT) 2 , 4 . The crystal structure and magnetic properties of these complexes are investigated by single-crystal X-ray diffraction, dc magnetization, infrared, and electron paramagnetic resonance spectroscopies. The compounds 1 and 4 crystallize in the triclinic, P 1̅, space group, whereas complex 3 crystallizes in the monoclinic structure with the C 2/ c space group and forms chain-like structure along the c direction. The complex 2 crystallizes in the monoclinic symmetry with the P 2 1 / c space group in which the N–O unit of the radical coordinates with the Co ion through hydrogen bonding of a water molecule. All compounds exhibit antiferromagnetic interactions between the transition metal ions and nitronyl nitroxide radicals. The magnetic exchange interactions ( J / K B ) are derived using isotropic spin Hamiltonian H = −2 J ∑( S metal S radical ) for the model fitting to the magnetic susceptibility data for 1 , 2 , 3 , and 4 . The exchange interaction strengths are found to be −328, −1.25, −248, and −256 K, for the 1 , 2 , 3 , and 4 metal–organic complexes, respectively. Quantum chemical density functional theory (DFT) computations are carried out on several models of the metal–radical complexes to elucidate the magnetic interactions at the molecular level. The calculations show that a small part of the inorganic spins are delocalized over the oxygens from hfac {∼0.03 for Co(II) and ∼0.015 for Mn(II)}, whereas a m...