Homoleptic Zinc(ll) Complexes with First and Second Coordination Shells of 5-tert-Butylpyrazole.

Reaction of hydrated Zn[NO3]2 or Zn[BF4]2 with four or more equivalents of 3{5}-tert-butylpyrazole (LtBu) yields [Zn(LtBu)4]X2 (X- = NO3- or BF4-). The nitrate complex contains C2-symmetric four-coordinate zinc(II) centers with a slightly flattened tetrahedral geometry, and each nitrate anion hydrogen bonds to two pyrazole N-H groups. Similar reactions with Zn[ClO4]2 or ZnCl2 in the presence of 2 equiv of AgPF6 or AgSbF6 yield instead [{Zn(LtBu)4}-(LtBu)4][ClO4]2 and [{Zn(LtBu)4}(LtBu)2]Y2 (Y = PF6- or SbF6-). Crystals of [{Zn(LtBu)4}(LtBu)4][ClO4]2 are composed of discrete [{Zn(LtBu)4}(LtBu)4]2+ supramolecules that are formed from N-H⋯N hydrogen bonding between zinc- bound and uncoordinated pyrazole rings. The [{Zn(LtBu)4}(LtBu)4]2+ moieties are linked into planar 44 nets by hydrogen bonding to bridging ClO4- anions. The ClO4- ions are almost perfectly encapsulated in near-spherical cavities of approximate dimensions 5.0 × 5.0 × 4.5 Åthat are formed by two interlocked supramolecular dications. Similarly, [{Zn(LtBu4)4}(LtBu)2][PF6]2 crystallizes as discrete supramolecules in the crystal with the PF6- anions occupying a shallow bowl-shaped cavity on the surface of the complex that is formed by two zinc-bound and one uncoordinated pyrazole ligands. ¹H NMR and IR studies of [{Zn(LtBu)4}(LtBu)4][ClO4]2 in CD2Cl2 imply that the second-sphere LtBu ligands dissociate from the [Zn(LtBu)4]2+ center in this solvent and that free and metal-bound LtBu are in rapid chemical exchange. [ABSTRACT FROM AUTHOR]