Competitive coordination aggregation for V-shaped [Co₃] and disc-like [Co₇] complexes: synthesis, magnetic properties and catechol oxidase activity

Abstract

Unique dependence on the nature of metal salt and reaction conditions for coordination assembly reactions of varying architecture and nuclearity have been identified in V-shaped [Co3L4] and planar disc-like [Co7L6] compounds: [CoL2(μ-L)2(μ-OH2)2(CF3CO2)2] (1) and [Co(μ-L)6(μ-OMe)6]Cl2 (2) (HL = 2-{(3-ethoxypropylimino)methyl}-6-methoxyphenol). At room temperature varying reaction conditions, cobalt-ligand ratios and use of different bases allowed unique types of coordination self-assembly. The synthetic marvel lies in the nature of aggregation with respect to the two unrelated cores in 1 and 2. Complex 1 assumes a V-shaped arrangement bound to L(-), water and a trifluoroacetate anion, while 2 grows around a central Co(II) ion surrounded by a {Co} hexagon bound to methoxide and L(-). Magnetic measurements revealed that the intermetallic interactions are antiferromagnetic in nature in the case of complex 1 and ferromagnetic in the case of 2 involving high spin cobalt(ii) ions with stabilization of the high-spin ground state in the latter case. In MeCN solutions complexes 1 and 2 showed catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBCH2) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ) in air. The kinetic study in MeCN revealed that with respect to the catalytic turnover number (kcat) 2 is more effective than 1 for oxidation of 3,5-DTBCH2.

Trapping of a Pseudotetrahedral CoIIO4 Core in Mixed-Valence Mixed-Geometry [Co5] Coordination Aggregates: Synthetic Marvel, Structures, and Magnetism

“…The absorption bands in the visible region with maxima (λ max ) at 557 nm (ε = 643 L mol –1 cm –1 ) and 555 nm (ε = 770 L mol –1 cm –1 ) for 1 and 2 , respectively, can be assigned to spin-allowed 4 A 2 → 4 T 1 (P) transitions originating from a Co II ion within distorted O 4 tetrahedral environments. , The lower energy shoulder peaks at 597 nm (ε = 510 L mol –1 cm –1 ) and 616 nm (ε = 501 L mol –1 cm –1 ) for 1 and 596 nm (ε = 610 L mol –1 cm –1 ) and 617 nm (ε = 501 L mol –1 cm –1 ) for 2 originates from the possible spin–orbit coupling of the 4 A 2 → 4 T 1 (P) absorption envelope in the presence of a low symmetry ligand field. , This fact suggests that the Co II centers are in a slightly distorted tetrahedral geometry. The four ligand-bound low-spin Co III centers, on the other hand, did not contribute anything for d–d transitions but showed phenoxido → Co III LMCT transitions at 383 nm (ε = 4800 L mol –1 cm –1 ) and 385 nm (ε = 5400 L mol –1 cm –1 ) for 1 and 2 , respectively . The intense and high-energy absorptions below 250 nm were attributed to intraligand π → π* LLCT transitions centered on CC and CN backbones of Co III - and Co II -bound anionic ligands.…”

“…The four ligand-bound low-spin Co III centers, on the other hand, did not contribute anything for d−d transitions but showed phenoxido → Co III LMCT transitions at 383 nm (ε = 4800 L mol −1 cm −1 ) and 385 nm (ε = 5400 L mol −1 cm −1 ) for 1 and 2, respectively. 42 The intense and high-energy absorptions below 250 nm were attributed to intraligand π → π* LLCT transitions centered on CC and CN backbones of Co III -and Co II -bound anionic ligands.…”

Entrapment of a Pseudo‐Tetrahedral CoII Center by Thioether Sulfur Bound {Co2(μ‐L)} Fragments: Synthesis, Field‐Induced Single‐Ion Magnetism and Catechol Oxidase Mimicking Activity

“…Dinuclear and otherc obalt(II/III) complexes were less extensively explored as synthetic mimics for catechol oxidation activity. [15][16][17][18] The nature of amine parts on the two sides of the ligand (H n L) backbonei si mportant from their cooperative effects for self-aggregation and trapping of substrates while showing functional behavior.T hus systematic variation of Xg roups between O, Na nd Si nH 2 N(CH 2 ) 2 X(CH 2 ) 2 OH (Figure 1) resulted in three different ligand types of contrasting coordination potential to 3d metal ions. When X = O, the resulting ligand 2,6bis[((2-(2-hydroxyethoxy)ethyl)imino)methyl]-4-methylphenol showeds elf-aggregation reactions of preformed {Co II 2 L} fragments for[ Co 5 ]c omplexes achievedf rom the trapping of a central Co II with the helpo fw ater-derived two HO À ands ix CH 3 COO À ions.…”

“…The synergism between the chosen ligand and used metal ions provides a strong influence on the affinity for substrate catechol. Dinuclear and other cobalt(II/III) complexes were less extensively explored as synthetic mimics for catechol oxidation activity …”

Temperature‐Sensitive Structural Speciation of Cobalt‐Iminodialcohol‐(N,N'‐Aromatic Chelator) Systems: Lattice Architecture and Spectrochemical Properties

“…Consequently, the chemical reactivity of Co(II,III) ion toward neutral (O,N,O)-terminal containing (amino)alcohol and carboxylic acid ligands stands as the basis for the development of materials exemplifying the diversity of structural motifs possessing specified physicochemical attributes. [30][31][32][33][34][35][36] Among such attributes included are the a) nuclearity of the cluster assembly at the binary-ternary metal-organic level, b) structural composition of the arising metal ionic assembly, c) molecular stoichiometry among the partners in the investigated systems, and d) the defined solvent system (e.g. alcohol) in which the chemical reactivity is probed into, with the oxidation state of the various metal centers playing a key role in the formulation of optical and magnetic properties in the emerging (oligo, multi)nuclear assemblies.…”