From 1D Helix to 0D Loop: Nitrite Anion Induced Structural Transformation Associated with Unexpected N‑Nitrosation of Amine Ligand

An infinite Ag­(I) coordination 41-helical chain, [Ag­(Hdpma)]­(NO3)2·H2O (1), was synthesized by the self-assembly of AgNO3 and di­(3-pyridylmethyl)­amine (dpma). Helix 1 is 5-fold interweaved and has a topological diamondoid-like net that is extended by ligand-unsupported helix-to-helix argentophilic interactions. Two identical diamondoid-like nets with opposite chiralities interpenetrate to form the whole 3D framework as a meso compound. Typical anion-exchange reactions cause a remarkable single-crystal-to-single-crystal (SCSC) structural transformation from the 1D helix 1 to the 0D molecular loop [Ag­(dpma-NO)­(NO2)]2 (2) (induced by the nitrite anion, NO2) and a 1D molecular ladder [Ag­(dpma)­(H2O)]­(NO3) (induced by the fluoride anion, F). Molecular loop 2 is an N-nitroso compound. This work is the first to present observations of nitrite-dominated in situ N-nitrosation of an amine ligand which accompanies SCSC structural transformation via an anion-exchange reaction.