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

Abstract

The mol-ecular 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-oct-yl) 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-di-chloro-ethane solvent mol-ecules in its crystal structure, whereas the other two are solvent-free. The compounds are tetra-butyl-aza-nium tetra-methyl-aza-nium hexa-μ₄-hydroxido-dodeca-μ₂-pyrazolato-hexa-hedro-octa-nickel, (C₁₆H₃₆N)(C₄H₁₂N)[Ni₈(C₃H₃N₂)₁₂(OH)₆] or (Bu₄N)(Me₄N)[Ni₈(μ₄-OH)₆(μ-pz)₁₂] (1), bis-(tetra-butyl-aza-nium) hexa-μ₄-hydroxido-dodeca-μ₂-(4-methyl-pyrazolato)-hexa-hedro-octa-nickel 1,2-di-chloro-ethane 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-(tetra-butyl-aza-nium) hexa-μ₄-hydroxido-dodeca-μ₂-(4-octylpyrazolato)-hexa-hedro-octa-nickel, (C₁₆H₃₆N)₂[Ni₈(C₁₁H₁₉N₂)₁₂(OH)₆] or (Bu₄N)₂[Ni₈(μ₄-OH)₆(μ-4-ⁿOctpz)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.

Keywords: crystal structure; nickel; octa­nuclear core; pyrazolate complex.

Figure 1

Displacement ellipsoid plot (50% probability) of the crystal structure of [Ni₈(μ₄-OH)₆(μ-pz)₁₂]²⁻ (1). Only atoms within the asymmetric unit are labeled; counter-ion disorder and H atoms are omitted for clarity.

Figure 2

Displacement ellipsoid plot (50% probability) of the crystal structure of [Ni₈(μ₄-OH)₆(μ-4-Mepz)₁₂]²⁻ (2). Only atoms within the asymmetric unit are labeled.

Figure 3

Displacement ellipsoid plot (50% probability) of the Bu₄N⁺ counter-ions and 1,2-di­chloro­ethane solvent mol­ecules in 2. Only atoms within the asymmetric unit are labeled; disorder and H atoms are omitted for clarity.

Figure 4

Displacement ellipsoid plot (50% probability) of the crystal structure of one [Ni₈(μ₄-OH)₆(μ-4- ⁿ Octpz)₁₂]²⁻ unit of 3. Only atoms within the asymmetric unit are labeled.

Figure 5

Displacement ellipsoid plot (50% probability) of the crystal structure of the other [Ni₈(μ₄-OH)₆(μ-4- ⁿ Octpz)₁₂]²⁻ unit of 3. Only atoms within the asymmetric unit are labeled.

Figure 6

Displacement ellipsoid plot (50% probability) of the Bu₄N⁺ counter-ions in 3. Disorder and H atoms are omitted for clarity.

Figure 7

Packing diagram of 1. Color scheme: green – Ni; red – O; blue – N; orange – C (pyrazolate ligand); black – C (counter-ions); white – H.

Figure 8

Packing diagram of 2. Color scheme: green – Ni; red – O; blue – N; orange – C (pyrazolate ligand); black – C (counter-ions); neon-green – Cl; white – H.

Figure 9

Packing diagram of 3 (disorder omitted). Color scheme: green – Ni; red – O; blue – N; orange – C (pyrazolate ligand); black – C (counter-ions); white – H.