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

An infinite Ag­(I) coordination 4<sub>1</sub>-helical chain, [Ag­(Hdpma)]­(NO<sub>3</sub>)<sub>2</sub>·H<sub>2</sub>O (<b>1</b>), was synthesized by the self-assembly of AgNO<sub>3</sub> and di­(3-pyridylmethyl)­amine (dpma). Helix <b>1</b> 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 <b>1</b> to the 0D molecular loop [Ag­(dpma-NO)­(NO<sub>2</sub>)]<sub>2</sub> (<b>2</b>) (induced by the nitrite anion, NO<sub>2</sub><sup>–</sup>) and a 1D molecular ladder [Ag­(dpma)­(H<sub>2</sub>O)]­(NO<sub>3</sub>) (induced by the fluoride anion, F<sup>–</sup>). Molecular loop <b>2</b> is an <i>N</i>-nitroso compound. This work is the first to present observations of nitrite-dominated in situ <i>N</i>-nitrosation of an amine ligand which accompanies SCSC structural transformation via an anion-exchange reaction.