Self-Assembled Tetra- and Pentanuclear Nickel(II) Aggregates From Phenoxido-Based Ligand -Bound {Ni₂} Fragments: Carboxylate Bridge Controlled Structures

Abstract

Three different carboxylato bridges (R = C2H5, CF3, and PhCH2 in RCO2(-)) have been used to obtain the supramolecular aggregates [Ni5(μ-H2bpmp)2(μ3-OH)2(μ1,3-O2CC2H5)6]·2H2O·4DMF (1·2H2O·4DMF), [Ni4(μ3-H2bpmp)2(μ3-OH)2(μ1,3-O2CCF3)2](CF3CO2)2·H2O (2·H2O), and [Ni4(μ3-H2bpmp)2(μ3-OH)2(μ1,3-O2CCH2Ph)2](PhCH2CO2)2·4H2O (3·4H2O) (H3bpmp =2,6-bis-[(3-hydroxy-propylimino)-methyl]-4-methyl-phenol) from the hydroxido-bridged dinuclear motif [Ni2(μ-H2bpmp)(OH)](2+). These complexes have been characterized by X-ray crystallography and magnetic measurements. A change from propanoate group to trifluoroacetate and phenylaceate groups provided different course of cluster assembly based on Ni2(μ-H2bpmp)2 fragments. The {Ni5(μ3-OH)2(μ1,3-O2CC2H5)6}(2+) core in 1 contains five Ni(II) ions in an hourglass (pentanuclear vertex-shared double cubane) arrangement. These compounds are new examples of [Ni5] and [Ni4] complexes where aggregation of the building motifs are guided by the nature of the carboxylate anions, which allows an effective tuning of the self-aggregate process within same ligand environment. The study of the magnetic properties reveals that 1 exhibits an S = 3 ground state. Nevertheless, the magnetization increases above the expected saturation value of 6 μB at higher fields, because of the suppression of antiferromagnetic exchange between the central and peripheral Ni(II) ions. Complexes 2 and 3 exhibit ferromagnetic exchange interactions that result in the S = 4 ground state. Examination of AC magnetic susceptibility showed that complex 2 in finely ground form behaves as spin glass with the spin-freezing temperature of ∼5.5 K. This behavior was attributed to the collapse of the structure upon the loss of interstitial solvent. Such property was not observed for complex 3, in which the bulkier carboxylate ligands provide for a more robust crystal packing and larger separation between the [Ni4O4] clusters.

Hydroxido-Supported and Carboxylato Bridge-Driven Aggregation for Discrete [Ni4] and Interconnected [Ni2]n Complexes

“…Ancillary bridges such as HO – , RO – , and N 3 – are known to be crucial to support the cubane, defective dicubane, and other higher order topologies . Until now numerous topologies have been reported, for example, cubane, , open dicubane, stepped cubane, tetrahedron, and pentanuclear vertex-shared double cubane of hourglass type (Scheme S1 in the Supporting Information, SI) …”

Hydrolytically active tetranuclear [NiII2]2 complexes: synthesis, structure, spectroscopy and phosphoester hydrolysis

“…11,12 Moreover, multinuclear nickel(II) complexes are relatively well-known for exhibiting magnetic interactions that are antiferro-or ferromagnetic in nature. [13][14][15][16][17][18][19][20][21][22][23] In these complexes, controlling the interactions among the metal ions provides a way to organize the overall spin ground state. Consequently, this can have a signicant implication on their magnetic behavior.…”

A Bioinspired Dinickel(II) Hydrolase: Solvent Vapor-Induced Hydrolysis of Carboxyesters under Ambient Conditions

“…Thus, the larger bridging angle along the hydroxo bridge leads to reasonable antiferromagnetic interaction between Ni1 and Ni3 with a J c of −49.7 cm –1 . Recently, two pentanuclear nickel­(II) clusters have been reported with similar topologies, like that of 2 , however, differing in the bridging groups. The exchange integral ( J ) values were lower than those of 2 , and in both reported cases, two magnetic-exchange values were observed …”