Cobalt complexes tetranuclear

Involvement of two nucleophilic nitrogen atoms is thus typical for the amino heterocycles. The mutual disposition of the pyridine and amine nitrogen atoms allows the formation of chelate structures for the cobalt complexes of purine, 221 and 222. Structures with the N, iV -five-membered metal cycles were proven for the tri- and tetranuclear complexes of silver ) with 8-aminoquinoline (223) (92IC4370), and polymeric copper- and rhodium-acetate clusters (224). Another coordination mode can be found in the complexes of 4-amino-3,5-bis(pyridin-2-yl)-l,2,4-triazole, (225 or... 

The N,S-chelate 2-aminoethanethiolate (aet-) forms stable cobalt(III) complexes, including clusters where the S can take on a bridging role. Reaction of [Co(NH3)5C1]2+ with Ni(aet)2 in water for several hours affords the black tetranuclear compound Co4(aet)8, which features act in simple chelate and bridging roles (245).1083 The simple monomeric complex [Co(aet)2(en)]+ has been reported 1084 when heated in water at 50 °C, the trimer Co Co(aet)3 2 is one product, with the central Co surrounded by six bridging S atoms. 

The tetranuclear and trinuclear clusters will only be observed at low pressures [8], but all other species are very common under hydroformylation conditions. Complex 4 is an ionic complex that is formed in polar solvents [9] and even hexa-solvated, divalent cobalt species may form as the cation. Under practical conditions both the dimers and the hydrides are observed, thus depending on the hydrogen pressure there will be more or less of the hydride present. 

The circular dichroism (CD) spectra of optically active di-, tri-, and tetranuclear complexes of chromium(III) and cobalt(III) have been reported and used to establish the complexes absolute configurations (55 59, 111, 115, 116, 152-157). The changes in circular dichroism resulting from ion pairing have been studied for the tetranuclear hexol Co j(OH)2Co(NH,)4J, h+ and have been shown to be attributable to the vicinal effect of the chiral oxygen centers produced stereospecifically by the ion-pair formation (56). For a series of trinuclear cobalt (III) amine complexes, cis-Co(CN)2[(OH)2Co(N4)2 J3 +, it was shown that the main CD contributions due to the two chiral Co(OH)4(CN)2 and Co(N4)(OH)2 centers are additive (155). In the case of the related tetranuclear complex Co((OH)2Co(en)2J,< + this postulate of additivity of CD spectra proved unsatisfactory (57). 

The oxidation of aqueous solutions of cobalt(II) salts in the presence of ligands may give a variety of products depending on the conditions. Air oxidation of Co(en)2(H20)22+ in the presence of charcoal as catalyst yields Co(en)33 +, and without charcoal catalyst the reaction gives either the peroxo-bridged dicobalt(III) complex (en)2Co(0H)(02)-Co(en)23+ or the tetranuclear complex Co (OH)2Co(en)2 36+, depending on the conditions. 

The tetranuclear cobalt(III) hexol reacts with cyanide (318) as shown in Eq. (23). The red trinuclear complex has been shown (49) by an X-ray... 

Bis(acetylacetonato)cobalt(II) and tris(acetylacetonato)cobalt(III) have both been found to possess fungicidal activity on treated cotton and linen fabrics.49 Both complexes have octahedral coordination about the metal, the cobalt(II) complex achieving this by forming a linear tetranuclear species (18). The latter complex is the somewhat more effective fungicide. 

Cobalt vapor was generated by directly heating a 0.01-in. ribbon filament of the metal and cocondensed with C2H4/Ar matrices at 12-15K. A series of mono- and binuclear cobalt-ethylene complexes Co(C2H4) (where / = 1, 2) and Co2(C2H4)OT (where m = 1, 2) as well as a suspected tetranuclear species Co4(C2H4)f have been detected by spectroscopic methods. 

The tetranuclear magnesium chelate complexes [(NH4)4n Mg4(L10 n)6 ] (29a,b) were first synthesized by reaction of dialkyl malonate 28, methylmagnesium iodide, and oxalyl chloride, followed by workup in aqueous ammonium chloride solution [102-105]. Now methyllithium/magnesium chloride instead of methylmagnesium iodide (direct method) is used, which by mere replacement of magnesium chloride by the chlorides of manganese, cobalt, and nickel also allows the synthesis of the corresponding tetranuclear complexes 29 (with Mn = Mn2+, Co2+, Ni2+) [103, 105]. 

Hanan GS, Volkmer D, Schubert US, Lehn JM, Baum G, Fenske D (1997) Coordination arrays tetranuclear cobalt(II) complexes with [2x2]-grid structure. Angew Chem Int Ed Engl 36 1842-1844... 

A recent investigation of this class of coordination arrays concerned the synthesis, structure and properties of stable tetranuclear cobalt(II) complexes of the ligand 4,6-bis(6-(2,2 -bipyridyl))pyrimidine and its derivatives, which have a grid-type structure ([2x2]-Grid) (35,36). Studies of the electronic, magnetic, and structural properties of these molecules on surfaces, as crystals, and in solution demonstrated interesting properties of these units (37,38). 

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