Co-Crystals and Salts Obtained from Dinitrogen Bases and 1,2,3,4-Cyclobutane Tetracarboxylic Acid and the Use of the Latter As a Template for Solid-State Photocyclization Reactions

The synthesis, isolation, and characterization of a series of co-crystals and adducts of 1,2,3,4-cyclobutane tetracarboxylic acid (H4CBTC) with the dinitrogen bases 1,2-bis(4-pyridyl)ethane (BPA) and 1,2-bis(4-pyridyl)ethylene (BPE), respectively, are reported. The thermal stability and interconversion process between the dihydrated salt [BPAH2][H2CBTC]·2H2O and its dehydration product and the use of this latter to obtain the neutral co-crystal [BPA]2·[H4CBTC] have been investigated. The products obtained with 1,2-bis(4-pyridyl)ethylene (BPE), namely, the salt [BPEH][H3CBTC] and the co-crystal [BPE]2·[H4CBTC] are prearranged in space so as to be able to react photochemically yielding rctt-tetrakis(4-pyridyl)cyclobutane (TPCB). Recrystallization from ethanol of the photocyclization products yields the channeled structure of the solvated co-crystal [TPCB]·[H4CBTC]·EtOH.