Metal Supramolecular Frameworks with Silver and Ditopic Bis(pyrazolyl)methane Ligands: Effect of the Anions and Ligand Substitution

Abstract

A study of the self-assembly of different silver salts and the potentially ditopic ligands bis­(pyrazol-1-yl)­(pyridine-4-yl)­methane (L1) and bis­(3,5-dimethylpyrazol-1-yl)­(pyridine-4-yl)­methane (L2) was undertaken and species’ with discrete or polymeric structures were obtained. Reactions with L1 always yielded derivatives that had a box-like cyclic dimer structure with two metal centers and two ligands. However, on using ligand L2, the resulting structure strongly depended on the coordination ability of the anion. On using anions that have coordinating ability (X = NO3 –, CF3SO3 –, PF2O2 –), a similar box-like structure was formed. However, the use of anions with lower coordinating ability (X = PF6 –, ClO4 –) led to coordination polymers with a helical disposition. Spontaneous resolution was observed in the two compounds, and only one enantiomer was present in the crystals studied. Solid-state circular dichroism spectroscopy was applied to bunches of crystals, and the results indicate that growth of single colonies of homochiral crystals starting from single nucleation points may take place. When the helical complexes were recrystallized, box-like cyclic dimers were obtained. The presence or absence of methyl groups on the pyrazolyl rings had a strong influence on the supramolecular structure. In solution, the box-like dimers containing L1 were more stable than those of L2.

A Single‐Step Reaction for Silicon and Germanium Nanorods

“…In all complexes the two Ag–N(pyrazole) bonds have different lengths. The Ag–O bonds are between 2.49 and 2.55 Å and these values are in the range reported for related complexes 23,10b,30…”

“…The use of metal centres that were able to give an octahedral geometry, such as Co II , Ni II and Zn II , led, in all cases, to the formation of box‐like cyclic dimers21 (Scheme ). Reaction of the ligands with silver(I) ions provided box‐like cyclic dimers and zig‐zag and helical polymers, with factors such as the coordinating ability of the anions and the crystallisation conditions affecting the structure obtained 22,23. The helical polymers exhibited spontaneous resolution and a conglomerate was formed 22,23.…”

“…Reaction of the ligands with silver(I) ions provided box‐like cyclic dimers and zig‐zag and helical polymers, with factors such as the coordinating ability of the anions and the crystallisation conditions affecting the structure obtained 22,23. The helical polymers exhibited spontaneous resolution and a conglomerate was formed 22,23. We also described the use of a two‐step methodology to obtain 2D coordination polymers with an egg‐crate structure from cyclic silver dimers, which acted as linear connectors, and hexamethylenetetramine 24…”

Bis(pyrazol‐1‐yl)(pyridin‐x‐yl)methane Ligands – Mono‐ or Ditopic Ligands in Complexes and Supramolecular Frameworks

“…The self‐assembly of ligands IIa , IIb ,, IIIa and IIIb with silver salts with anions of different coordination ability gave rise to a wide variety of compounds. Undoubtedly the stereochemical non‐rigidity of the silver ion plays a major part in this behaviour.…”

Supramolecular Assembly of Metal‐Organic Tubes Constructed from the Ditopic Heteroscorpionate Ligand (4‐NH2C6H4)CHpz2 (pz = Pyrazol‐1‐yl) and Silver(I)

“…Heteroditopic bis(pyrazolyl)methanes (pyrazolyl = pz) with secondary Lewis donors bound to the methine group are ligands with a proclivity for forming metallacycles and, thus, are of potential interest for assembling into tubes. Manzano's 4‐pyridyl derivatives L ( * )py (top left, Scheme ) readily form cyclic dimeric structures (bottom middle, Scheme ) with a variety of metals . Especially noteworthy is [Ag(L* py )](PF 6 ) · 0.125 THF · 0.125 CH 2 Cl 2 , which was shown to crystallize with a polymeric (bottom left, Scheme ) helical tube structure.…”