Aromatic sulfonamides exist in a synclinal conformation with the twisted structure arising from rotation around the S-N bond in both the solid state and in solution. Simple bidentate ligands containing the sulfonamide moiety can be extended to form elongated ligands, and optically active components can be added to form a versatile building block for the construction of coordination polymers with many structures. Mixing the simple ligands 1 and 2 and the elongated ligands 3 and 4 with different Ag(I) salts yielded the corresponding complexes [Ag(1)OTf]_n (1a), [Ag(2)]_n•nOTf(2a), [Ag(3)OTf]_n (3a), [Ag(3)]_n•nBF₄ (3b), [Ag(4)CH₃CN]_n•nBF₄•nCHCl₃ (4b), and [Ag(4)]_n•nSbF₆•nCH₄O (4c). Straight chains and racemic helical polymers were observed in the crystal structure of complexes 1a and 2a, respectively. In the crystal structures of complexes 3a and 4b, infinite 1D straight chains containing a T-shaped coordination geometry about the Ag(I) centers were formed by the reaction of ligands 3 or 4 with Ag(I) salts in CH₃CN/CHCl₃. A continuous 1D coordination polymer containing a racemic mixture of left- and right-handed helices formed in the crystal structure of complex 3b. Furthermore, a layered coordination polymer consisting of a racemic mixture of left- and right-handed polymers was observed from the crystal structure of complex 4c. The construction of optically pure left- or right-handed 1D helical polymers via the introduction of chiral functional groups on the nitrogen atom of the sulfonamide ligand is currently under investigation in our laboratory.

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Nonalternant hydrocarbons, which involve odd-membered rings, are an intriguing family for investigations of the structure-property relationship of π-conjugated carbocycles. Bicyclic nonalternant hydrocarbons, azulene, pentalene and heptalene, are the most fundamental molecules in a series of nonalternant hydrocarbons. Over the last 15 years, the chemistry of nonalternant hydrocarbons has experienced a remarkable renaissance mainly thanks to advances in synthetic methodologies. Ring-annulated nonalternant π-systems, in which some benzenoid rings are attached into the nonalternant frameworks, are the key players in their resurgence. The ring annulation impacts the electronic structures of nonalternant subunits, which modulates the HOMO-LUMO gap and creates perturbations in their inherent (anti)aromatic nature. The tunable, narrow HOMO-LUMO gap has offered rich studies into the electronic properties of open-shell characters and into their potential applications as functional organic optoelectronic materials. This article describes our recent studies on the synthesis and characterization of π-extended nonalternant hydrocarbons, containing azulene, pentalene and heptalene frameworks.

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