Tridentate Chelate Compounds. V. Coordination Compounds Derived from Cobalt Salts and 1,3-Disubstituted 1,2-Diaza-2-propenes

Chiswell, B.; Geldard, John F.; Phillip, Arpad T.; Lions, Francis

doi:10.1021/ic50019a017

Cited by 32 publications

(11 citation statements)

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“…Spectroelectrochemical experiments were performed for complex 11 in order to ascertain the site of reduction (Figure 7). The band at 488 nm in the unreduced complex is assigned to a ligand‐centred (LC) π–π* transition, since an absorption twice the intensity is observed at 483–485 nm for grids 4 – 6 , and because bands at 485/495 nm occur in mononuclear cobalt( II ) complexes that contain deprotonated pyridylhydrazone ligands 35. The LC band undergoes a blue shift to 460 nm during the first reduction step, while the absorption at 322 nm decreases and exhibits a small bathchromic shift of 7 nm.…”

Section: Resultsmentioning

confidence: 99%

Mixed‐Valence, Mixed‐Spin‐State, and Heterometallic [2×2] Grid‐type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical Features

Uppadine

Gisselbrecht

Kyritsakas

et al. 2005

Chemistry A European J

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An extended family of heterometallic [(M1)2(M2)2(L-)4](n+) [2x2] grid-type arrays 1-9 has been prepared. The three-tiered synthetic route encompasses regioselective, redox and enantioselective features and is based on the stepwise construction of heteroditopic hydrazone ligands A-C. These ligands contain ionisable NH and nonionisable NMe hydrazone units, which allows the metal redox properties to be controlled according to the charge on the ligand binding pocket. The 2-pyrimidine (R) and 6-pyridine (R') substituents have a significant effect on complex geometry and influence both the electrochemical and magnetic behaviour of the system. 1H NMR spectroscopic studies show that the Fe(II) ions in the grid can be low spin, high spin or spin crossover depending on the steric effect of substituents R and R'. This steric effect has been manipulated to construct an unusual array possessing two low-spin and two spin-crossover Fe(II) centres (grid 8). Electrochemical studies were performed for the grid-type arrays 1-9 and their respective mononuclear precursor complexes 10-13. The grids function as electron reservoirs and display up to eight monoelectronic, reversible reduction steps. These processes generally occur in pairs and are assigned to ligand-based reductions and to the Co(III)/Co(II) redox couple. Individual metal ions in the heterometallic grid motif can be selectively addressed electrochemically (e.g., either the Co(III) or Fe(II) ions can be targeted in grids 2 and 5). The Fe(II) oxidation potential is governed by the charge on the ligand binding unit, rather than the spin state, thus permitting facile electrochemical discrimination between the two types of Fe(II) centre in 7 or in 8. Such multistable heterometallic [2x2] gridlike arrays are of great interest for future supramolecular devices incorporating multilevel redox activity.

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Section: Resultsmentioning

confidence: 99%

Mixed‐Valence, Mixed‐Spin‐State, and Heterometallic [2×2] Grid‐type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical Features

Uppadine

Gisselbrecht

Kyritsakas

et al. 2005

Chemistry A European J

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“…This is followed by organic extraction and solvent evaporation but there is a high probability of halide contamination from the starting compound. Chiswell et al (11) reacted papyri and cobalt(II) salts to yield the deprotonated cobalt(III) compounds [Co(papyH)(papy)] z+ and [Co(papy)2] + but were unable to isolate the neutral cobalt(lI) chelate because of complexation accompanied by oxidation and proton loss. Failure to isolate these complexes was in part due to the use of H20 as the reaction medium.…”

Section: Resultsmentioning

confidence: 99%

Electrosynthesis and magnetic behaviour of neutral cobalt(II) complexes of pyridine-2-carbaldehyde pyridin-2?-ylhydrazone (papyH) and its analogues

Vecchio-Sadus

1995

Transition Met Chem

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Neutral cobalt(II) complcxcs with the tridentatc N-hetcrocyclic ligand pyridine-2-carbaldehyde pyridin-2'-ylhydrazone (papyri) and its analogues have been prepared by the electrochemical oxidation of cobalt in an acetone H solution of the hydrazone. The [Co(papy)2 ] complexes Me are obtained as red-green dichroic microcrystals due to Me the extended re-conjugation system in the anionic ligand. H The magnetic moments of the octahedral cobalt(II) chelates H decrease continuously from/~ff = 1.81-4.63 B.M. at room H temperature to 1.7-4.08 B.M. at ca. 90K. The changes H H in magnetic moment have been accounted for by a H "~T~.-+2E spin crossover system.

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“…[46] Ligand exchange reactions employing metal halide or pseudo-halide precursors are known to lead preferably to complexes of the type metal/ligand = 1:1, [19][20][21][22] whereas employing precursors with noncoordinating counterions leads to complexes of the type 2:1. [18,[24][25][26] Nitrate precursors seem to exhibit reactivity at the borderline, enabling both stoichiometries. Thus, fine-tuning of electronic and steric properties on the pyridazine ring results in two different metal-to-ligand ratios.…”

Section: Solid State Structures Of the Complexesmentioning

confidence: 99%

“…PAPHY was first described in 1957 [16] and subsequently extensively studied. [17][18][19][20][21][22] Throughout the literature two types of complexes, namely the mono [23] and the bis complex [24] can be found for this ligand type, depending on the donor ability of the counterion. The observed poor stabilities in solution and the easy deprotonation of the hydrogen atom at the hydrazone backbone represent the major drawbacks in PAPHY complexes, as the pH value must be kept within small ranges.…”

Section: Introductionmentioning

confidence: 99%

Pyridazine‐Based Ligands and Their Coordinating Ability towards First‐Row Transition Metals

et al. 2010

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Tridentate pyridazine ligands with two different substituents at the 3-and 6-positions (pyridyl hydrazone at the 3-position and tolyl 3 tol or tert-butyl 3 tBu at the 6-position) were prepared in high yields from 3,6-disubstituted pyridazine hydrazines and pyridine aldehyde by Schiff base condensation. This provides a facile entry into a novel class of heterocyclic molecules exhibiting interesting coordinating abilities. They react with first-row transition metal nitrates to yield complexes of the type [ tol form complexes of the ML 2 type, whereas with ligand 3 tBu exclusively complexes of the ML type are formed,

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Tridentate Chelate Compounds. V. Coordination Compounds Derived from Cobalt Salts and 1,3-Disubstituted 1,2-Diaza-2-propenes

Cited by 32 publications

References 0 publications

Mixed‐Valence, Mixed‐Spin‐State, and Heterometallic [2×2] Grid‐type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical Features

Mixed‐Valence, Mixed‐Spin‐State, and Heterometallic [2×2] Grid‐type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical Features

Electrosynthesis and magnetic behaviour of neutral cobalt(II) complexes of pyridine-2-carbaldehyde pyridin-2?-ylhydrazone (papyH) and its analogues

Pyridazine‐Based Ligands and Their Coordinating Ability towards First‐Row Transition Metals

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