Anaerobic solid-phase thermal tetrahedral-to-octahedral transformation of some cobalt (II) complexes

New examples of thermal tetrahedral-to-octahedral transformation were observed and studied by the thermal reactions of disodium tetrakis(aryloxo)cobaltate(ii) complexes,na2[co(oar)4(thf)m](thf)n [oar = o-chloro-,o-bromo-,m-chloro-,p-bromo-,2,4-dichloro-,2,4-dimethyl- or 2,6-dichlorophenoxide; m = 2 (m = 0 for 2,4-dimethylphenoxide complex; n = 1-3) in the solid phase. with one exception,the original complexes were all violet and have octahedral configurations. the exception was na2[co(2,4-(me)2c6h32o)4].thf,which has an intense blue color and its electronic and magnetic data were characteristic for tetrahedral cobalt(ii) complexes. the aryloxide complexes of 2,6-dichloro-,m-chloro-,and p-bromophenoxide showed a two-step thermochromism (violet→blue→rose) upon heating. these steps may be due to the structure changes to tetrahedral thf-free complexes and then to an aryloxide bridged polymers containing octahedral cobalt(ii) ions. the complexes of o-chloro- and o-bromophenoxide were underwent to thermal desolvation-polymerization in one step,changing directly into the rose aryloxide bridged polymers. the complex of 2,4-dichsorophenoxide showed only one-step thermochromism (violet→blue),thus changing from octahedral to tetrahedral configuration. whereas the complex of 2,4-dimethylphenoxide did not show any color change and retained its tetrahedral structure till decomposition. the reverse changes of the thermal products proceeded on standing under dry thf atmosphere,for some hours or days.