CHARGE-DISTRIBUTION DEPENDENT ON THE CHELATING RATIO - [CO(MU-BPYM)(DBBQ)(2)] VS [(CO(DBBQ)(2))(2)(MU-BPYM)] (BPYM=2,2'-BIPYRIMIDINE DBBQ=3,6-DI-T-BUTYL-1,2-BENZOQUINONE)

The preparation and characterization of [Co(mu-bpym)(dbbq)(2)] and [{C o(dbbq)(2)}(2)(mu-bpym)] (bpym = 2,2'-bipyrimidine; dbbq = 3,6-di-t-bu tyl-1,2-benzoquinone) have been established. The temperature-dependent magnetic moments (100-400 K) and variable-temperature near-infrared ( NIR) absorption spectra are presented to show that the title complexes exhibit an equilibrium via a catechol to a cobalt intramolecular elec tron transfer. At temperatures below 200 K the mononuclear complex [Co (mu-bpym)(dbbq)(2)] has a charge distribution of [Co-III(mu-bpym)(dbca t)(dbsq)] (dbsq = 3,6-di-t-butyl-1,2-semiquinonato; dbcat = 3,6-di-t-b utylcatecholato), whereas at temperatures beyond 290 K the mononuclear complex is predominantly In the [Co-II(mu-bpym)(dbsq)(2)] form. From 200-290 K a mixture of Co(III) and Co(II) redox isomers exists at equi librium in the solid state. In particular, a thermal analysis of a sol id sample of the mononuclear complex discloses that the transition for the Co(III)/Co(II) is accompanied by a change in the heat content of 36 kJ mol(-1), which may be closely related to the band at 3878 cm(-1) , assigned as a dbcat to Co(III) charge transfer. In striking contrast , the dinuclear complex [{Co(dbbq)(2)}(2)(mu-bpym)] is locked in a cha rge distribution of [{Co-II(dbsq)(2)}(2)(mu-bpym)] when the temperatur e is 100-400 K.