Cobalt imidazole complexes

For unsubstituted purines, the most probable site for coordination is the imidazole nitrogen (N-9), which is protonated in the free neutral ligand. An example is the cobalt complex of adenine, [Co(ad)2(H20)4]+ (9-XXII). 

Cobalt Complexes. A fair number of complexes of cobalt have been studied theoretically. Veillard and co-workers have studied the Schiff base adduct Co(acacen)L02 (L = none, H2O, CO, CN", imidazole) and the porphyrin complex Co(porph)(NH3)02 using ab initio LCAO SCF methods. The calculations show the structure to be more stable than the if a linear structure is also found to be unstable. The most important interaction is that between the cobalt d a orbital and the in- plane rg orbital. The interactions of the in-plane jig orbital with the dyz orbital and TTg (i) with dxz, although present, are much less than in the analogous iron complexes as a result of the tighter binding of the d-orbitals in cobalt. The unpaired electron is localised essentially in the Tig (1) orbital of dioxygen. 

NjPtSioHg, Platinate(II), bis(pentasuIfido)-, bis(tetrapropylammonium), 21 13 NzPtSijHg, Platinate(IV), tris(penta-sulfido)-, diammonium, 21 12, 13 N2SCH4, Urea, thio-chromium(O) complexes, 23 2 N2SC2, Sulfur dicyanide, 24 125 N2SC4H6, 2H-Imidazole-2-thione, 1,3-di-hydro-1-methyl-cobalt complexes, 23 171 N2SCSH12, Thiourea, N,N,N methyl-... 

Despite the weak basicity of isoxazoles, complexes of the parent methyl and phenyl derivatives with numerous metal ions such as copper, zinc, cobalt, etc. have been described (79AHC(25) 147). Many transition metal cations form complexes with Imidazoles the coordination number is four to six (70AHC(12)103). The chemistry of pyrazole complexes has been especially well studied and coordination compounds are known with thlazoles and 1,2,4-triazoles. Tetrazole anions also form good ligands for heavy metals (77AHC(21)323). 

Table 12 shows the cis effect of the axial ligand X or L on the optical spectrum of cobalt(III) etioporphyrin derivatives Co(Etio-I)LX [32a-h] which behave similarly to the corresponding rhodium(III) complexes (Table 4). Analogous trends are found in the Co(TTP)LX series (133). The only notable feature is the large bathochromic shift caused by benzimidazole in [32h] obviously this ligand is far more different from pyridine than imidazole, the condensed ring system acting as a stronger 7r-acceptor.

Reactions of cobalt porphyrin with p-fluoranyl or phenyl-A -butylimidazole proceeds analogously—both fluoranyl and imidazole coordinate with the cobalt contained in the porphyrin complex, but fluoranyl was fixed in its semiquinone, anion-radical form (Okamoto and Fukuzumi 2003). 

The complexes [LCo(p-02)(p-OH)CoL] [L = en, trien, dien, tetra-ethylenepentamine, or tris-(2-aminoethyl)amine] have been studied, and the new complexes [[Co(imidazole)(gly)2 202],4H20 [ Co2(imidazole)2-(gly)402 0H],3H20, and [Co(imidazole)(gly)2(02)H20] have been prepared The spectroscopic properties of various p-peroxo- and p-superoxo-cobalt(iii) complexes have been examined. The singly-bridged p-peroxo-compounds have a strong band at 300 nm, whereas this falls at 350 nm for p-peroxo-p-hydroxo-complexes and two peaks at 480 and 700 nm are observed for p-superoxo-species. The i.r. spectra of p-peroxo-bridged complexes of cobalt(iii)-cyclam have been reported. ... 

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