Cobalt, crystal structure

Cobalt. - Crystal structures are reported for the phosphine substituted complex [Co2(C0)g(PMe3)2] and for the alkynyliron bridged species [Co2((t-PhCsCFp) (CO)g].240 studies of the radical anion [CO2(C0)2 (PF2)2NMe>3r indicate that the unpaired electron is in an intermetallic a molecular orbital mainly composed of cobalt orbitals.241 The coupling of alkylIdene with CO in complexes [Co2 /t-CHR)(jx-L)( -dppm)(CO)4] to yield ketenes has been studied under CO or S02. ... 

Quite recently, Ciampolini and coworkers have reported the synthesis of two isomeric mked oxygen-phosphorus macrocycles and the crystal structures of their cobalt complexes. Synthesis of macrocycle 27 was accomplished by condensation of 1,2-bis-(phenylphosphino)ethane dianion with 2,2 -dichlorodiethyl ether in THE. The two isomers of 27 were isolated in 1.5% and 2% yield. The synthesis is formulated in Eq. (6.17), below. 

This study could be extended to the synthesis of iron nanoparticles. Using Fe[N(SiMe3)2]2 as precursor and a mixture of HDA and oleic acid, spherical nanoparticles are initially formed as in the case of cobalt. However, a thermal treatment at 150 °C in the presence of H2 leads to coalescence of the particles into cubic particles of 7 nm side length. Furthermore, these particles self-organize into cubic super-structures (cubes of cubes Fig. ) [79]. The nanoparticles are very air-sensitive but consist of zerovalent iron as evidenced by Mossbauer spectroscopy. The fact that the spherical particles present at the early stage of the reaction coalesce into rods in the case of cobalt and cubes in the case of iron is attributed to the crystal structure of the metal particles hep for cobalt, bcc for iron. 

Figure 1 Publications per year featuring cobalt complexes (unshaded bars) and publications reporting at least one crystal structure of a Co-containing complex (shaded bars).

The symmetrical dimer [(Me3P)3CoH]2(//-N2) is formed by protonation of the dinitrogen cobaltate precursor and its crystal structure is reported.131 The complex reversibly binds N2, forming the monomer CoH(N2)(PMe3)3. 

In contrast with the Schiff base salen, salicylaldehyde oxime (79) (salox) complexes of Co have received comparatively little attention, but a series of bis-bidentate divalent complexes of the form iraiis-Co(sa 1 ox)2( D M SO)2 have been reported.343 The heterocyclic bidentate oxime violurate (lH,3H-pyrimidine-2,4,5,6-tetrone 5-oximate, Hvi) (80) and its /V-methyl (mvi) and /V,/V -dimethyl (dmvi) derivatives form high-spin divalent [Co(vi)]+ and Co(vi)2 complexes, whereas [Co(vi)3] is low spin.344 The mixed-ligand Co(dmvi)2(phen) complex is also low spin. The crystal structure of m-Co(pxo)2Br2 (pxo = 2-acetylpyridine-l-oxide oxime) is isostructural with the Ni11 relative.345 The dichloro complex also adopts a cis configuration. The tridentate dioximes 2,6-diformyl-4-methylphenol dioxime and 2,6-diacetyl-4-methylphenol dioxime (Hdampo) form binuclear complexes of the type (81a) and (81b) respectively.346 Cobalt oxide nanoparticles were prepared by... 

Cobalt(II) alkoxides are known and monomeric forms are part of a wider review.413 The interest in these compounds pertains to a potential role in catalysis. For example, a discrete cobalt(II) alkoxide is believed to form in situ from a chloro precursor during reaction and performs the catalytic role in the decomposition of dialkyl pyrocarbonates to dialkyl carbonates and carbon dioxide.414 A number of mononuclear alkoxide complexes of cobalt(II) have been characterized by crystal structures, as exemplified by [CoCl(OC(t-Bu)3)2 Li(THF)].415 The Co ion in this structure and close relatives has a rare distorted trigonal-planar coordination geometry due to the extreme steric crowding around the metal. 

Chelated species are less common. The substituted thiourea 7V-ethoxycarbonyl-/V-[3-(/>-anisyl) pyrazol-5-yl]thiourea (eatu) acts as a monoanionic 0,S-chelate to cobalt(II), forming Co(eatu)2.506 Whereas ethylenethiourea (etu) has been observed to act as a S-donor monodentate in Co (etu)2X2(H20)2 (X = C1, Br), it binds as an S,N-chelate in Co(etu)2(OOCCH3)2.507 Both violet octahedral and blue tetrahedral cobalt(II) compounds Co(pptu)2Cl2 and Cp(pptu)Cl2 respectively were prepared with bidentate A -2-(5-pico 1 y 1)- A"-pheny 11hiourea (pptu) chelated.508 Refluxing Co powder with thiourea in 4-methylpyridine provides a route to isothiocyanates, which form by decomposition of thiourea to ammonium thiocyanate509 with one product, Co(pic)4(NCS)2, characterized by a crystal structure. 

Cobalt complexes of the fused 7-membered ring unsaturated analogs of the dibenzo-[14] tetraazaannulenes, the tropocoronands (H2TC), have also been reported. The crystal structure... 

Cobalt(III) complexes of formula cis- and trans-[Co(dtc)L4]2+ and [Co(dtc)2L2]+ where dtc = dimethyl-, diethyl- or piperidino-dithiocarbamate were prepared with phosphites P(OMe)3, P(OEt)3 and 4-ethyl-2,6,7-trioxa-l-phophabicyclo[2.2.2]octane as ligands L.1048 Whereas Co—P bonding is found, as defined in the crystal structures of each of the two forms of complexes isolated, a linkage isomer in which the phosphite is O bound was detected for the bis(dithio-carbamate) compounds. 

Examples in organometallic systems are known. Reaction of thiuram disulfides, (R2NCS2)2, with Co(Cp)(CO)2 produces dithiocarbamato pseudo-octahedral cobalt(III) complexes Co(Cp)(dtc)2 with one chelated and one monodentate dtc, also accessible via Co(Cp)I(dtc).1050 Fluxional behavior, including monodentate chelate exchange, was observed for some complexes in temperature-dependent NMR studies. The Co(Cp)I(dtc) complex was defined in a crystal structure. 

Thiosemicarbazone (RNH-CS-NH-N=CR/R//, tsc) complexes of cobalt(III) have been extensively studied since the early 1980s and continue to attract attention, gaining particularly from an interest in their biological activity and potential cytotoxicity. A truly extensive range of tsc compounds has now been reported, although structural definition of their complexes widely relied on basic analytical and spectroscopic techniques up to the late 1980s, when X-ray crystal structural studies of tsc compounds became more common. A review of thiosemicarbazone and S-alkyldithiocarbazate complexes has appeared.1053... 

Figure 3.7 The crystal structure of DtxR, a 226-residue three-domain dimeric protein, is shown. The protein, activated by cobalt (designated 1 and 2), is bound to a 21-bp DNA duplex based on the consensus operator sequence. Two DtxR dimers surround the DNA duplex, which is distorted compared to canonical B-DNA. Only domain 1, involved in DNA-binding, and domain 2, involved in dimer formation, are shown. The helices of the DNA-binding domain are indicated by HI, H2, and H3. H3 binds to the major groove of the DNA. From Pohl et al., 1999, by permission of Academic Press. 

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