Co II Compounds

Abstract This review deals with spin crossover effects in small polynuclear clusters, particularly dinuclear species, and in extended network molecular materials, some of which have interpenetrated network structures. Fe(II)Fe(II) species are the main focus but Co(II)Co(II) compounds are included. The sections on dinuclear compounds include short background reviews on (i) synergism of SCO and spin-spin magnetic exchange (ii) cooperativity (memory effects) in polynuclear compounds, and (iii) the design of dinu-... 

Summing up, one can conclude that all the magnetic interactions found for Co(aca-cen) in Ni(acacen) 1/2 H20 are compatible with a 2A2, yz) ground state of this low-spin Co(II) compound. 

Reactions of transition-metal coordinated olefins with diazo compounds as a route to cyclopropane products have not yet been rigorously established. Catalysts that should be effective in this pathway are those that are more susceptible to olefin coordination than to association with a diazo compound and also those whose coordinated alkene is sufficiently electrophilic to react with diazo compounds, especially diazomethane. Pd(II), Pt(II), and Co(II) compounds appear to be capable of olefin coordination-induced cyclopropanation reactions, but further investigations will be required to unravel this mechanistic possibility. 

The Co(II) compounds are usually low-spin, five-coordinate monomeric species, LCo(DH)2(II) (II). However, L2Co(DH)2 low-spin compounds can be isolated (II). These latter materials are known to be five coordinate in solution and have EPR and visible spectra and magnetic moments ( 2 BM) identical to those of LCo(DH)2 (12). The X-ray structure of neither type of solid is known when L = P-donor ligand but the bis(pyridine) compound has been characterized structurally (13) and exhibits long Co-N(pyridine) bonds of 2.25 A. 

The Co(II) compounds react with alkyl halides according to Equation 1. The initial and rate-determining step is halogen abstraction (14). For L = phosphines... 

Methyl cobalamin is usually described as a Co(II) compound, which changes to Co(III) on dissociation of CH3. Describe the probable electronic structure (splitting of d levels and number of unpaired electrons) of the cobalt in both cases. 

Finally, we address the question of the reasons for the superiority of Co(II) compounds as the catalysts for the alkene epoxidation by 02/aldehyde system. We have studied the catalytic activity of Co(II) compounds using imKS-stilbene as a model substrate. Kinetic curves for the Iran -stilbene epoxide accumulation are given in Fig. 3. The kinetic curves show autocatalytic character. The time of the complete alkene conversion depends on both the induction time and the rate of the reaction after the completion of the induction period. It should be noted that the induction time increases considerably with decreasing aldehyde concentration and goes through a maximum with increasing Co(II) concentration (in the range 10 - 10 M). One can see from Fig. 3 that the rate of the epoxidation lowers in the order PW1 iCo, CoW 12 > CoNaY, Co(N03)2 >CoPc. 

Magnetic studies for the Ni(II)Co(II) and Cu(II)Co(II) compounds have been reported158, as well as the theoretical treatments suitable for those cases. 

Sulphites rarely occur in natural waters. They are chiefly of artificial origin (wastewaters from the production of sulphite cellulose and thermal processing of coal). They are washed out into atmospheric waters from urban and industrial air pollutants. In waters, sulphites are slowly oxidized into sulphates, consuming dissolved oxygen. Chemical oxidation is accelerated by catalytic effects of various metals, particularly the Co(II) compounds. In water treatment, sulphites are used for dechlorination, removal of oxygen from feed waters for steam boilers, and in the technology of wastewaters for reduction of Cr(VI) to Cr(III). 

The grid-type architecture of the complexes was confirmed by the determination of the crystal structure of the Co(II) compound [Co4(2)4](SbF6)8 (Figure 5) (36). The metal ions are in a distorted octahedral coordination environment. 

With the exception of Co +, mononuclear complexes of d metals are rather rare. Moreover, molecular Co(II) compounds do not seem to be luminescent. Observations on the emission of Co(II) are essentially restricted to solid state systems. The tetrahedral [0004] moiety incorporated in various host lattices is well known to show an LF emission [40], e.g.. 

The rate of initiation at the beginning of the process is 30 times lower than that in the stationary phase. Thus, the processes on the surface must determine the rate of chain generation, and free radicals are not formed in the bulk solution. At the beginning of the process (in the absence of ROOH) Co(II) compounds can interact with O2 with formation of free radicals (Eq. (12-21))... 

Co2(CO)g] and [Co4(CO)i2] are air-sensitive however, large crystals of these compounds do not undergo noticeable oxidation in a short period of time. Solutions of these carbonyls rapidly undergo decomposition. The halogens quantitatively oxidize [Co2(CO)g] and [ 04(00)12] to Co(II) salts. Oxidizing acids oxidize [Co2(CO)g] to Co(II) compounds and nonoxidizing acids react with this carbonyl only slowly and partially. 

The solution preparation of Co(II) coordination compounds containing ligands 1-4 was already reported in the literature [31]. Nevertheless, we have been able to prepare the same compounds using solvent-free mechanochemical synthesis, quantitatively and only in 20 minutes. These complexes were characterized by XRPD and SCXRD, when possible. Interestingly, the Co(II) compound containing ligand 2 was proven to be isostructural with the corresponding Ni(II) compound. 

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