Synthesis, magnetic properties, redox behaviour, and crystal structure of the bridged binuclear nickel(<scp>II</scp>) complex [Ni2(µ-OH)(µ-CH3CO2)2L2]ClO4·H2O

Chaudhuri, Phalguni; Küppers, H.; Wieghardt, Karl; Gehring, S.; Haase, Wolfgang; Nuber, Bernhard; Weiß, Johannes

doi:10.1039/dt9880001367

Cited by 61 publications

(34 citation statements)

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“…In principle, powder measurements are not ideally suited for a thorough analysis of S 1 dinuclear systems; however, the intradimer exchange term J often proves to be the dominant term in the spin Hamiltonian, [21] and accordingly neglect of both a zero-field splitting parameter D and interdimer interactions z'J' results in a fit of reasonable quality in the present case (Figure 2). The value of J À 56.9 cm À1 in 1´(BPh 4 ) 2 lies in the upper range of the exchange interactions reported previously for OH À or pyrazolate-bridged nickel(ii) dimers.…”

Section: Resultsmentioning

confidence: 80%

“…The value of J À 56.9 cm À1 in 1´(BPh 4 ) 2 lies in the upper range of the exchange interactions reported previously for OH À or pyrazolate-bridged nickel(ii) dimers. [13,21,22] Magnetostructural relationships for dinuclear Ni II systems are not yet as elaborated as the detailed correlations noted in Cu II /Cu II chemistry, [18,23] but only recently a linear dependence of the antiferromagnetic exchange coupling constant on Ni-O-Ni bridge angles as well as on the intramolecular Ni´´´Ni distances in a series of doubly phenoxy-bridged dinickel(ii) complexes emerged.…”

Section: Resultsmentioning

confidence: 99%

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Cooperative Transformations of Small Molecules at a Dinuclear Nickel(II) Site

et al. 1999

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Using the possibility of tuning the metal ± metal distance in pyrazolatebased bimetallic complexes by the length of the chelating side arms attached to the heterocycle, we have synthesized related dinickel(ii) complexes in which either a hydroxide (1) or a H 3 O 2 unit (2) spans the two metal centers within the bimetallic pocket. Complex 1 exhibits strong antiferromagnetic coupling mediated by the bridging hydroxide unit (J À 56.9 cm À1 ), while 2 shows Curie ± Weiss behavior over a wide temperature range. The H 3 O 2 unit in 2 acts like the resting form of an active metalbound hydroxide and allows the study of cooperative transformations of small molecules at a dinickel(ii) site relevant to the active site of the metalloenzyme urease. Firstly, it mediates the hydration of various nitriles to give the respective m-amidato-N,O-bridged complexes 3 a ± c. Reaction of 2 with urea affords complex 5 with an N,O-bridging deprotonated urea, which when heated releases ammonia to yield the cyanato-bridged dinickel(ii) compound 4. This product is also obtained when 2 is treated with dimethylcyanamide. Unactivated amides dimethylformamide (DMF) and dimethylamide (DMA) are hydrolyzed by 2 only sluggishly, while the stoichiometric hydrolysis of esters such as ethyl acetate and ethyl propionate runs more cleanly to afford the carboxylato-bridged bimetallic complexes 10 b and c. Likewise, hydrolytic cleavage occurs with g-butyrolactone to give complex 10 d. We propose that these reactions proceed by cooperative action of the two metal ions within the bimetallic pocket of the dinickel(ii) core. Possible alternatives are addressed by investigation of analogous mononuclear nickel(ii) complexes 8 a and b in conjunction with a corresponding dimeric compound 9 and by the reaction of 2 with an excess of acetate to yield the dinickel(ii) complex 11, in which a formerly chelating side arm has been driven out of the coordination sphere. Complexes 1´(BPh 4 ) 2 , 2( BPh 4 ) 2 , 3c´(ClO 4 ) 2 , 4´(BPh 4 ) 2 , 8 b( ClO 4 ) 2 , 9´(ClO 4 ) 2 , 10 d´(ClO 4 ) 2 , and 11´(ClO 4 ) have been characterized structurally by X-ray crystallography.

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Section: Resultsmentioning

confidence: 80%

Section: Resultsmentioning

confidence: 99%

Cooperative Transformations of Small Molecules at a Dinuclear Nickel(II) Site

et al. 1999

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“…For comparison, the Ni-O distances of 2.156(8) and 2.153(9) Å in [Ni 2 50 are significantly longer than the 2.014(7) Å distance in [Ni 2 (µ-OH)(µ-OAc) 2 (Me 3 TACN) 2 ]-(ClO 4 ). 60 61 The pK a value of metal-bound water molecules is affected by the metal ion and its oxidation states as well as by the ancillary ligands and local dielectric. 22 Proton Shifts in Carboxylate-Bridged Dimetallic Centers.…”

Section: Discussionmentioning

confidence: 99%

Sterically Hindered Carboxylate Ligands Support Water-Bridged Dimetallic Centers That Model Features of Metallohydrolase Active Sites

et al. 2002

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The synthesis and characterization of carboxylate-bridged dimetallic complexes are described. By using m-terphenyl-derived carboxylate ligands, a series of dicobalt(II), dicobalt(III), dinickel(II), and dizinc(II) complexes were synthesized. The compounds are [Co(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (1), [Co(2)(mu-OH(2))(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (2a-c), [Co(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (3), [Ni(2)(mu-O(2)CAr(Tol))(4)L(2)] (4), [Ni(2)(mu-HO...H)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (5), and [Zn(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (6), where Ar(Tol)CO(2)H = 2,6-di(p-tolyl)benzoic acid and L = pyridine, THF, or N,N-dibenzylethylenediamine. Structural analysis of these complexes revealed that additional bridging ligands can be readily accommodated within the [M(2)(mu-O(2)CAr(Tol))(2)](2+) core, allowing a wide distribution of M...M distances from 2.5745(6) to 4.0169(9) A. Unprecedented bridging units [M(2)(mu-OH(2))(2)(mu-O(2)CR)(2)](n+) and [M(2)(mu-HO...H)(2)(mu-O(2)CR)(2)](n+) were identified in 2a-c and 5, respectively, in which strong hydrogen bonding accommodates shifts of protons from bridging water molecules toward the dangling oxygen atoms of terminal monodentate carboxylate groups. Such a proton shift along the O...H...O coordinate attenuates the donor ability of the anionic carboxylate ligand, which can translate into increased Lewis acidity at the metal centers. Such double activation of bridging water molecules by a Lewis acidic metal center and a metal-bound general base may facilitate the reactivity of metallohydrolases such as methionine aminopeptidase (MAP).

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“…[32] Relatively few bis(µ-pyrazolato)-bridged high-spin dinickel() complexes have been previously structurally charac- terized, [22,33,34] and even fewer have been studied with respect to their magnetic properties, [35] which precludes any definite magneto-structural correlations at the present stage. However, the rather large magnetic coupling in 1 is certainly due to the high degree of planarity of the Ni(NN) 2 Ni scaffold, in accordance with the magneto-structural trends observed in bis(µ-pyrazolato) dicopper() chemistry.…”

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confidence: 99%

Pyrazolate‐Based Dinucleating Ligands in L₂M₂ Scaffolds: Effects of Bulky Substituents and Coligands on Structures and M···H−C Interactions

et al. 2004

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A series of nickel(II) and palladium(II) complexes [L 2 M 2 ] 2+ have been prepared and structurally characterized, where L is a pyrazolate ligand with bulky 2,6-dimethyl-or 2,6-di(isopropyl)anilinomethyl side arms. Coordinating counter anions such as chloride can bind to axial sites of the dinickel species in a solvent-dependent process, giving rise to five-coordinate high-spin metal ions. In the case of weakly coordinating anions, the metal ions are found in roughly square-planar environments, and the structures are governed by the tendency of the bulky aryl groups to avoid each other, which forces the methyl or isopropyl substituents in the aryl 2-and 6-positions to approach the metal ions from the axial directions. This leads to drastic low-field shifts of the respective 1 H NMR signals, e.g. δ = 7.86 ppm for the isopropyl −CH which comes in

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Synthesis, magnetic properties, redox behaviour, and crystal structure of the bridged binuclear nickel(II) complex [Ni₂(µ-OH)(µ-CH₃CO₂)₂L₂]ClO₄·H₂O

Cited by 61 publications

References 1 publication

Cooperative Transformations of Small Molecules at a Dinuclear Nickel(II) Site

Cooperative Transformations of Small Molecules at a Dinuclear Nickel(II) Site

Sterically Hindered Carboxylate Ligands Support Water-Bridged Dimetallic Centers That Model Features of Metallohydrolase Active Sites

Pyrazolate‐Based Dinucleating Ligands in L₂M₂ Scaffolds: Effects of Bulky Substituents and Coligands on Structures and M···H−C Interactions

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Synthesis, magnetic properties, redox behaviour, and crystal structure of the bridged binuclear nickel(II) complex [Ni2(µ-OH)(µ-CH3CO2)2L2]ClO4·H2O

Cited by 61 publications

References 1 publication

Cooperative Transformations of Small Molecules at a Dinuclear Nickel(II) Site

Cooperative Transformations of Small Molecules at a Dinuclear Nickel(II) Site

Sterically Hindered Carboxylate Ligands Support Water-Bridged Dimetallic Centers That Model Features of Metallohydrolase Active Sites

Pyrazolate‐Based Dinucleating Ligands in L2M2 Scaffolds: Effects of Bulky Substituents and Coligands on Structures and M···H−C Interactions

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Synthesis, magnetic properties, redox behaviour, and crystal structure of the bridged binuclear nickel(II) complex [Ni₂(µ-OH)(µ-CH₃CO₂)₂L₂]ClO₄·H₂O

Pyrazolate‐Based Dinucleating Ligands in L₂M₂ Scaffolds: Effects of Bulky Substituents and Coligands on Structures and M···H−C Interactions