Bis[μ-3-(pyridin-2-yl)pyrazolato]bis[acetato(3,5-dimethyl-1H-pyrazole)nickel(II)]

The title compound is a dimeric nickel(II) coordination compound containing two different substituted pyrazoles ligands, namely 3,5-dimethylpyrazole and 3-(pyridin-2-yl) pyrazole along with acetate.


Structure description
Noble metals such as palladium, platinum or iridium are widely used in catalysis due to their desirable properties such as the ability to tolerate variable coordination states and oxidation states that predispose them towards catalysing two-electron redox processes, while at the same time also being sufficiently stable and thermally stable to be of practical use.A major drawback is, however, their high price and limited availability.As an alternative to scarce 4 and 5d metals, their more earth-abundant 3d congeners have been investigated, and in particular several nickel-catalysed organic transformation strategies were developed and established (Wilke, 1988;Keim, 1990;Montgomery, 2004;Tasker et al., 2014;Diccianni et al., 2020).These include C-C and C-X (X = heteroatom) crosscoupling (Rosen et al., 2011), cycloaddition (Lautens et al., 1996;Komagawa et al., 2013), asymmetric hydrogenation (Vermaak et al., 2024), photoredox catalysis (Milligan et al., 2019;Cuesta-Galisteo et al., 2024), reductive coupling (Day et al., 2023) and reductive cyclization reactions (Montgomery, 2004) to name just a few.The inability of nickel to catalyse two-electron transformations can be overcome by the placement of more than one metal atom at the catalytic centre, and dinuclear nickel complexes show an enhanced catalytic activity and a higher robustness that can be traced back to the synergistic interaction between the two metals in the active site (Uyeda & Farley 2021;Xu et al., 2020).Nickel is also a micronutrient and essential for the biosynthesis of hydrogenase, carbon monoxide dehydrogenase (CODH) and urease.These enzymes require more than one metal active site to catalyse the enzymatic process.This also substantiates the crucial role of the presence of more than one metal centre for 3d-metalbased catalysts.
Compound 1 crystallizes in the monoclinic P2 1 /n space group, in which the asymmetric unit contains half of the molecule.Compound 1 is a dinuclear heteroleptic nickel(II) complex consisting of two each of anionic 2-PyPz, anionic Compound 1 exhibits several intra-and intermolecular hydrogen bonds (Table 1, Fig. 2), with atom N6 of Me 2 PzH data reports IUCrData (2024).9, x240810

Synthesis and crystallization
0.5 mmol of Ni(OOCCH 3 ) 2 •4H 2 O (0.1244 g) was dissolved in 30 ml of methanol.Then, 0.5 mmol of 2-PyPzH (0.0726 g) and 0.79 mmol of triethylamine (0.11 ml) were added to the solution.Upon addition of these, the solution became milky white and insoluble.It was stirred for 2 h.After every 30 minutes of stirring, 0.5 mmol of lipophilic Me 2 PzH (0.2402 g, 2.5 mmol) and equal portions of triethylamine (0.11 ml, 0.79 mmol) were added.The solution slowly turned green and was further stirred for 12 h.It was then filtered and solvents were evaporated in vacuo to obtain a pale-green solid.Finally, the solid was recrystallized from methanol solution, which afforded blue crystals of 1. Crystal yield 45%

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

data reports
3 of 4   Crystal data

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.All the non-hydrogen atoms were refined anisotropically using full-matrix least-square procedures while carbon bound hydrogen atoms were included in idealized positions and the methyl CH 3 were allowed to rotate using a riding model.C-H bonds were constrained to 0.95 Å for aromatic C-H (U iso (H) = 1.2 U eq (C)) and 0.98 Å for CH 3 [U iso (H) = 1.5 U eq (C)] units, respectively.The N-H proton was added from the difference Fourier map and refined with U iso (H) = 1.2 U eq (N).

Figure 2
Figure 2 Perspective view of 1 showing the intra-(red and black dotted lines) and intermolecular C-H� � �O (pink dotted lines) and intramolecular N-H� � �N (blue and black dotted lines) interactions with bond distances (several atoms were removed for clarity).

Table 2
Experimental details.