Cobalt dipositive

This first case is the least interesting, although it is by far the most common result in putative template reactions, even when the metal ion is apparently the right size for the desired product A good example is found in the reaction presented in Fig. 6-29. All of the dipositive first-row transition metal ions have similar sizes, but only nickel(n) is effective for the formation of complexes of 6.30 in a template condensation. The other metals either give polymers, complexes of 6.31, or in the case of cobalt(n), compounds that are halfway to the desired product containing 6.32. 

DIISOTHIOCYANATOTETRAPYRIDINE AND DIISOTHIOCYANATODIPYRIDINE COMPLEXES OF DIPOSITIVE FIRST-TRANSITION-METAL IONS (MANGANESE, IRON, COBALT,... 

The nitrite ion is an excellent coordinating agent, generally forming metal —N02 bonds (although there are a few cases of metal —ONO bonds reported). One of its most interesting reactions takes place with dipositive cobalt in the presence of dilute acid. In this reaction, part of the nitrite coordinates With the cobalt, and part of the nitrite oxidizes the cobalt to the +3 state (NO being formed). Thus one cobalt ion consumes seven nitrite ions to yield the complex Co(N02)e8, the ion often used in qualitative analysis to precipitate potassium from solution. 

Despite the vast number of cobalt(IT) complexes known, the dipositive oxidation state is rare for rhodium. The bulk of the rhodium(ri) complexes known are dimeric, the classic examples being the diamagnetic carboxylato complexes that adopt the classic lantern structure (26). However, even the aqua complex is dimeric so the bridging carboxylato ligands are not essential for the formation of the rhodium-rhodium bond. 

Table 2. The mean wavenumber (ircm ), from the first moment of the integrated band area, and the observed and the calculated [Eqs. (5) and (6)] oscillator strength (f/10 ) of the d-d transitions to the Ti (F) and Ti (P) excited state of the cobalt(II) tetrahalides from the A2 ground state, together with the temperature coefficient (C/10 ) of the summed dipole strengths of the two transitions [Eq. (IS)] from X The theoretical f-values are minimal, calculated from the expectation value, tr ) = 0.3661 A, appropriate for a dipositively charged metal ion in the complex...

As a preliminary, let us recall that the first transition series includes the elements Sc (scandium), Ti (titanium), V (vanadium), Cr (chromium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Cu (copper), and Zn (zink), with the atomic numbers 21-30. The ground electron configuration of a dipositive transition element is that of an argon core 1 s22s22p63s23p6 plus a partly filled 3d shell,... 

The only known solid compounds containing the ion Co(H20)6 are the sulfate Co2(S04)3 18H20 and its alums. Although the first synthesizer of the sulfate reported he was able to store it in a stoppered tube for months without visible decomposition, later authors stated that this compound and the ammonium alum decompose at laboratory temperature within a few hours. By an improved drying procedure, the cesium alum is readily obtained in a form in which even the magnetic susceptibility (a very sensitive criterion for the presence of dipositive cobalt) shows that only very slow decomposition occurs. Use of this... 

A basic product of the approximate composition (OH)Co(N3) is made by heating an aqueous cobalt azide solution to precipitate a violet solid. Dipositive cobalt forms a tetraazidocobaltate(II) complex, [Co (N3)4] ", in aqueous cobalt(II) salt solutions with a 15-fold sodium azide excess at pH 5 and may be... 

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