Planar Benzo[1,2-b:4,5-b′]dithiophene Derivatives Decorated with Nitronyl and Imino Nitroxides

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 (Jintra,exp/kB) 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 (zJinter,exp/kB) 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 Jintra and Jinter. In addition, we also extracted a coupling within the chain of Jchain/kB = −2.2 K and a coupling between the chains of zJinterchain = −1.5 K for BDTTh2–NN by a Heisenberg chain model. Intra- and intermolecular interactions and spin densities were examined by DFT studies.