Influencing the Stability of Diaminomethane‐Containing Azacrown Ether Ligands in the Presence of Transition‐Metal Ions

The evaluation of a new azacrown ether ligand bis{[3‐(pyridin‐4‐yl)‐1 H ‐pyrazol‐1‐yl]methyl}diaza‐18‐crown‐6 ( b3pd ), which contains pendant p ‐pyridylpyrazole arms connected by diaminomethane linkers, identified a tendency to undergo retro‐Mannich fragmentation in the presence of transition‐metal ions. However, treatment of b3pd with potassium perchlorate or potassium iodide prior to complexation with transition‐metal ions imparted a resistance to fragmentation, such that crystallisation of coordination polymers from concentrated solutions after several weeks was possible. Four solid‐state structures containing K b3pd were isolated: a perchlorate salt ( 1 ), a divalent manganese 1D coordination polymer [Mn(K b3pd )(DMF) 4 ] · 2ClO 4 · I 3 ( 2 , DMF = N , N ‐dimethylformamide), a cuprous 2D coordination network [Cu 2 (K b3pd ) 2 (I 3 )(I) 3 ] · 3H 2 O ( 3 ) and a cuprous 1D coordination polymer [Cu(K b3pd )(I) 2 ] ( 4 ). Additionally, the retro‐Mannich process was investigated by in situ FTIR spectroscopy, mass spectrometry, crystallography and by the isolation of a cobalt complex ligated by a partially fragmented ligand, mono{[3‐(pyridin‐4‐yl)‐1 H ‐pyrazol‐1‐yl]methyl}diaza‐18‐crown‐6 ( m3pd ). The composition of the cobalt complex was found to be [CoCl 3 (H m3pd )] · H 2 O ( 5 ).