An octanuclear nickel(II) pyrazolate cluster with a cubic Ni₈ core and its methyl- and n-octyl-functionalized derivatives

Abstract

The molecular and crystal structure of a discrete [Ni8(μ4-OH)6(μ-4-Rpz)12]2− (R = H; pz = pyrazolate anion, C3H3N2 −) cluster with an unprecedented, perfectly cubic arrangement of its eight Ni centers is reported, along with its lower-symmetry alkyl-functionalized (R = methyl and n-octyl) derivatives. Crystals of the latter two were obtained with two identical counter-ions (Bu4N+), whereas the crystal of the complex with the parent pyrazole ligand has one Me4N+ and one Bu4N+ counter-ion. The methyl derivative incorporates 1,2-dichloroethane solvent molecules in its crystal structure, whereas the other two are solvent-free. The compounds are tetrabutylazanium tetramethylazanium hexa-μ4-hydroxido-dodeca-μ2-pyrazolato-hexahedro-octanickel, (C16H36N)(C4H12N)[Ni8(C3H3N2)12(OH)6] or (Bu4N)(Me4N)[Ni8(μ4-OH)6(μ-pz)12] (1), bis(tetrabutylazanium) hexa-μ4-hydroxido-dodeca-μ2-(4-methylpyrazolato)-hexahedro-octanickel 1,2-dichloroethane 7.196-solvate, (C16H36N)2[Ni8(C4H5N2)12(OH)6]·7.196C2H4Cl2 or (Bu4N)2[Ni8(μ4-OH)6(μ-4-Mepz)12]·7.196(ClCH2CH2Cl) (2), and bis(tetrabutylazanium) hexa-μ4-hydroxido-dodeca-μ2-(4-octylpyrazolato)-hexahedro-octanickel, (C16H36N)2[Ni8(C11H19N2)12(OH)6] or (Bu4N)2[Ni8(μ4-OH)6(μ-4- n Octpz)12] (3). All counter-ions are disordered (with the exception of one Bu4N+ in 3). Some of the octyl chains of 3 (the crystal is twinned by non-merohedry) are also disordered. Various structural features are discussed and contrasted with those of other known [Ni8(μ4-OH)6(μ-4-Rpz)12]2− complexes, including extended three-dimensional metal–organic frameworks. In all three structures, the Ni8 units are lined up in columns.