Cobalt complexes volume changes

An interesting example is the iron(III) dimethyldithiocarbamato complex [181] [Fe((CH3)2NC(S)S)3] where the unit cell amounts to 44.4 per Fe atom or 26.7 cm mol This value is somewhat higher than the AF° values of Table 16. It should be noted, however, that the dithiocarbamato complex is of [Fe Sg] type, whereas the iron(III) complexes in Table 16 are examples of the type [Fe -N4.02]. As far as cobalt(II) is concerned, for the complex [Co(nnp)(NCS)2] where nnp = AT-[(diphenylphosphino)ethyl]-JV -diethylethyl-enediamine [182, 183], the volume change has been obtained as 21.5 per Co atom or 13.0cm mol S whereas for [Co(terpy)2]l2 2H20 [132] where terpy = 2,2, 2"-terpyridine, the corresponding results are 33.7 A per Co atom or 20.3 cm moP Again this value is higher than the AV° value for the closely related [Co(terpy)2]Cl2 complex of Table 16. 

The brown //-peroxo complex Kg[(CN)jCo—O2—Co(CN)5] H20 is prepared" " by rapidly bubbling oxygen gas or air through a freshly prepared cold (0°C) solution containing cobalt(II) chloride or nitrate (0.4M) and KCN (2.1M). After the bubbling has proceeded for 5-10 min, the solution is diluted with an equal volume of EtOH at 0°C and the product is filtered off, washed first with EtOH and then with EtjO and dried in vacuo over cone H2SO4. Under these conditions 60% yields are obtained but if the concentrations are changed appreciably or the addition of O2 is slow, lower or no yields are obtained. 

The Co longitudinal relaxation rates of tris(acetylacetonato)cobalt(lIl) in dichrolo-methane and benzene were measured over the concentration range between 20 and 110 mol m 3 at several temperatures. The dependence of the relaxation rate on the temperature and the complex concentration is primarily attributable to the change in the viscosity of solutioa The values of eQqlh were calculated from the concentration dependence of the Co relaxation rate by using the Debye-Stokes-Einstein equation and the Einstein relationship between molar volume and viscosity B coefflcienL... 

The outer-sphere electron transfer reaction between the cobalt (III) complex [(en)2Co(/i-NH2,02)Co(en)2r and the 2,2,6,6-tetramethyl-l-piperidinyloxyl radical was found to have a volume of activation of 0.2 0.5 cm mor which differs negligibly from zero. ) result endorses the contention that the changes in solvation and in intrinsic volume are responsible, respectively, for determining... 

For the acid-independent and acid-dependent aquation pathways of [Co(NH3)sS04], the respective volumes of activation A Vo (at zero pressure) and AVh (pressure averaged over 100 MPa) are -18.3 and -3.5cm mor at 35°C and -19.7 and -3.9cm mor at 55° and / = 1.0 The temperature dependence of A Vo can be accounted for in terms of solvational change indicated by its pressure dependence. The work also questions the common supposition that the molar volumes V of the penta- and hexacoordinate ammine complexes of the same metal ion are equal and suggests that there is a difference of 17-20 cm moV for the cobalt(III) case. 

Anation of irans-[M(L)(OH2)2] ions [L = mcso-tetrakis(p-sulfonato-phenyOporphyrinate ion M = Co, Rh, Cr] by NCS has been studied at high pressures. The volumes of activation and other activation parameters are compared in Table 6.8. Whereas the values of A5 would suggest a change in mechanism from dissociative for Co " to associative for Rh " and Cr ", the values of A V show that all three metals react dissociatively. The cobalt system is so labile that high-pressure stopped flow was needed to measure AV, and a D mechanism was found to operate in this case. The Rh " and Cr " complexes anate with an Id mechanism. ... 

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