Fields singlet-triplet

A second example is the recently reported singlet-triplet equilibrium in a Mo(II) complex, cis-[Mo(bipy)2(OPri)2] (31). The interpretation of the magnetism is complicated by the possibility that the equilibrium is not entirely metal centered, but involves charge transfer to the bi-pyridyl ligands. Because a strong field is required to spin pair the d4 configuration, however, it is not impossible that examples exist among Mo(II) chemistry. The possible dynamics are subject to considerations similar to those which apply to Mn(III). 

According to this sequence, formation of cis- and tnms-stilbenes is preceded by formation of a magnetosensitive ion radical by a singlet-triplet conversion. This means that spin polarization must be observed in cis- and fram-stilbenes, and the isomerization rate must depend on the intensity of the magnetic field. These predictions were confirmed experimentally (Lyoshina et al. 1980). Hence, the ion radical route for trans/cis conversion is the main one under photoirradiation conditions. Until now, the mechanisms assumed for such processes have involved energy transfer and did not take into account donor-acceptor interaction. This interaction makes the process energetically more favorable. 

The most recent experimental determination of oAp.ps is that of Al-Ramadhan and Gidley (1994). The apparatus and analysis techniques are similar to those of Westbrook et al. (1989) and will therefore not be described here. Their method used the effect of singlet-triplet mixing in a static magnetic field (Gidley et al., 1982) this allowed oAp-Ps to be... 

Fig. 27 Magnetic heat capacity for PhBABI for 7 < 100 K showing variation with external magnetic field (left) zero-field magnetic heat capacity showing fits (right) to ID AFM chain, 2D AFM square planar, 2D AFM square planar bilayer, singlet-triplet spin pairing (ST), and spin ladder models.

ZT Y r A A A A A AC dimensionless thermoelectric figure of merit electronic coefficient of heat capacity (1+ZT)F2 crystal field singlet non-Kramers doublet (crystal field state) crystal field triplet crystal field triplet hybridization gap jump in heat capacity at Tc K KL -min P 6>d X JCO total thermal conductivity of solid thermal conductivity of electrons or holes thermal conductivity of lattice minimum lattice thermal conductivity electrical resistivity Debye temperature magnetic susceptibility magnetic susceptibility at T = 0... 

The Mossbauer spectra (between 4.2 K and 298 K) show two overlapping doublets with temperature dependent relative intensities. In conjunction with the data from magnetic susceptibility measurements (between 83 and 313 K) the Mossbauer spectra were interpreted in terms of a singlet triplet spin transition of the central iron(II) ion. No internal magnetic field was observed in a Mossbauer experiment under applied field at 4.2 K. The authors consider this complex the first authentic example of a singlet < triplet spin transition in the 3 d6 configuration of iron(II). Support has been received from UV-vis spectra and IR vibrational spectra201). 

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