Li+, Cu+, and Ag+ oligonuclear structures with the sterically demanding bis(3,5-tertbutylpyrazol-1-yl)dithioacetate heteroscorpionate ligand.

The heteroscorpionate N(2)S(2) donor ligand bis(3,5-tertbutylpyrazol-1-yl)dithioacetate (L) was prepared as a Li(+) trinuclear complex, which co-crystallizes with tetrahydrofuran (THF) solvent molecules: [Li(L)](3) x (2.25)THF. When [Li(L)](3) was reacted with AgBF(4) or [Cu(CH(3)CN)(4)]BF(4), the oligonuclear species [Ag(L)](3) and [Cu(5)(L)(4)]BF(4) were isolated and structurally characterized. The Ag(+) complex presents an irregular trinuclear structure in which three AgL moieties define a central trigonal site that may potentially host a fourth metal ion. The Cu(+) complex exhibits a highly symmetric pentanuclear structure in which four equivalent CuL moieties shape an internal tetrahedral site occupied by an additional Cu(+) ion. According to electrospray-mass spectrometry (ESI-MS) and (1)H diffusion NMR spectroscopy, the Ag(+) and Cu(+) complexes maintain oligonuclear structures in solution. In particular, the Cu(+) pentanuclear complex, once dissolved, rapidly equilibrates with the tetranuclear species [Cu(4)(L)(3)](+). This is confirmed by the presence of two sets of NMR signals, which demonstrated a change in ratio at different complex concentrations effected by a NMR dilution titration. Variable temperature NMR experiments (210-303 K) defined the activation parameters associated with the fluxional behavior of [Cu(5)(L)(4)]BF(4) and [Cu(4)(L)(3)](+), and these results are consistent with intramolecular rearrangements in both species (DeltaS(double dagger) < 0).