Molecular Iodine Stabilization in an Extended N•••I-I•••N Assembly

The adduct [bis(quinoxaline)-2,2',3,3'-disulfide-I-2](infinity) (Q(2)S(2)center dot I-2)(infinity) can be easily synthesised from the reaction of Q(2)S(2) and I-2 in CH2Cl2 or, in the absence of any solvent, through diffusion of I-2 vapours at 60 degrees C. X-ray diffraction analysis shows the presence of an extended N center dot center dot center dot I-I center dot center dot center dot N assembly in which each I-2 molecule links a Q(2)S(2) molecule at both ends through a nitrogen atom to form a polymeric species; the d(I-I) and d(N-I) bond lengths confirm a very weak nitrogen-iodine interaction at the base of the N center dot center dot center dot I-I center dot center dot center dot N assembly. DFT calculations provide optimised distances for the N center dot center dot center dot I and I-I bonds and explanation for the zigzag chain formation: the mPW1PW functional and the B3LYP hybrid functional with a variety of basis sets for the I atomic species [CRENBL, LANL2DZ, LANL2DZ(d,p), LANL08(d), SBKJC, SBKJC polarised-LFK and Stuttgart RLC] have been tested. Compound 1 proved stable up to nearly 100 degrees C, and the stability is to be mainly attributed to the lattice energy of its polymeric structure then to donor-acceptor stabilisation. The facile insertion of molecular iodine into the Q(2)S(2) network makes this compound an interesting iodine sponge, suitable for I-2 storage; moreover, Q(2)S(2) can easily collect and release I-2(g) by a temperature-controlled process (60 and 97 degrees C, respectively). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)