Cu11 mononuclear complex

Each Cu1 center (gray ball) is bound to an imine and to a pyridine nitrogen atom from each strand and shows a rather distorted tetrahedral coordination geometry. On the other hand, Fig. 2.15, which displays the molecular structure of the [Cun(16)](CF3S03)2 salt, shows that the Cu11 ion prefers to form a mononuclear complex species. 

Figure 2.18 A square scheme illustrating the disassembling of the [Cu2(16)2]2 + double helicate complex, following Cu -to-Cu" oxidation, and the consequent assembling of two [Cun(16)]2+ mononuclear complexes, following the Cu"-to-Cu reduction. The process ultimately derives from the geometrical coordinative preferences of the two oxidation states Cu1 prefers a tetrahedral coordination, which can be achieved with the double helicate arrangement Cu11 prefers a square coordination geometry, which is fulfilled by the coordination of a single molecule of 16.

The protonation constants of the ligands L9, L11, L14, and L1S (Scheme 5), having one, two or three aminoethyl or three aminopropyl pendant arms, respectively, on the [9]aneN3 framework, and the thermodynamic stabilities of their mononuclear complexes with Cu11 and Zn11 have been investigated by potentiometric measurements in aqueous solutions (Table 1) [51],... 

In 1996 Stack and co-workers reported an unusual 3 1 (copper 02 stoichiometry) reaction between a mononuclear copper(I) complex of a A-permethylated (lR,2R)-cyclohexanediamine ligand with dioxygen. The end product of this reaction, stable at only low temperatures (X-ray structure at —40 °C) is a discrete, mixed-valence trinuclear copper cluster (1), with two Cu11 and a Cu111 center (Cu-Cu 2.641 and 2.704 A).27 Its spectroscopic and magnetic behavior were also investigated in detail. The relevance of this synthetic complex to the reduction of 02 at the trinuclear active sites of multicopper oxidases4-8 was discussed. Once formed, it exhibits moderate thermal stability, decomposed by a non-first-order process in about 3h at —10 °C. In the presence of trace water, the major isolated product was the bis(/i-hydroxo)dicopper(II) dimer (2). 

Compartmental pyrazole ligands (14) can be used to form bimetallic complexes (15).157 This ligand enforces a separation distance between the metal ions. Stability constants were calculated showing a stability for both mononuclear and dinuclear compounds that was less than Cu11 but greater than Nin. 

Recently several new active site model compounds have been prepared (Carrier et al., 1991) using sterically hindered tris(pyrazoyI)hydroborate (L) and tris(thioethyl)amine (L2) as ligands. The copper nitrite complex LCu11 (N02) models the enzyme substrate complex and X-ray studies confirm that the complex is tetrahedral. A mononuclear copper—nitrosyl complex similar to postulated NO adducts of copper proteins has also been prepared from LCu1 (MeCN) and NO, which has been tentatively identified as a Cu11 -NO species on the basis of IR (v NO 1711 cm 1) and ESR evidence. 

In contrast to iron and cobalt, end-on superoxo-copper(II) species do not dominate the field of copper-oxygen chemistry. In 1 1 copper-dioxygen adducts, an alternative side-on, t 2 coordination mode is sometimes observed these [(L)Cu11 (t 2-(02 ")] or [(L)Cum-(ri2-(022 )] complexes are discussed below. Mononuclear copper-dioxygen complexes easily react with the second molecule of the Cu(I) complex, forming peroxo- or dioxo-bridged dinuclear species (Section 4.4). For sterically unhindered... 

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