Doublet stability

X. Li and J. Paldus, ]. Chem. Phys., 102, 2013 (1995). Spin-Adapted Open-Shell State-Selective Coupled-Cluster Approach and Doublet Stability of Its Hartree-Fock Reference. 

For simple open-shell systems, we formulated analogous doublet stability conditions [102,103], and illustrated them on a series of polyenic radicals [104]. These type of solutions do not fit into Fukutome s classification, but have now been incorporated in its generalized version [100]. The doublet stability conditions were formulated just at the time of the 1968 Soviet invasion of Czechoslovakia [105], which greatly upset the everyday life of all citizens, not to mention the culmral and scientific activities in the entire country. For this reason. Jiff and myself gratefully welcomed the hospitality the University of Waterloo kindly provided, thanks to the efforts of Professor Sydney Davison, not knowing at the time that it would become our permanent abode. Thus, the bulk of our work on the stability problem was carried out at Waterloo. 

J. Paldus and A. Veillard, Mol. Phys., 35,445 (1978) and references therein. Doublet Stability... 

Important information relating to the intramolecular interaction in dinuclear units of [Fe(phdia)(NCS)2]2(phdia) can be drawn from the study of the LIESST effect at low temperature. The Mossbauer spectrum recorded at 4.2 K after slow cooling reveals 16.0% of HS and 84.0% of LS species (Fig. 17a). The spectrum recorded after the irradiation (1=488 nm) of the sample for one hour at 4.2 K shows an increase of the intensity of the HS doublet up to 25.0% (Fig. 17b). The spectrum recorded subsequently in a magnetic field reveals no [HS-HS] pairs it consists of 50.0% of [HS-LS] and 50% of [LS-LS] pairs (Fig. 17c). This is further evidence of the inherent stability of mixed pairs in [Fe(phdia)(NCS)2]2(phdia). ... 

The majority of gold(I) ylide complexes prepared have been of a binu-clear constitution. The first compound of this type was obtained (56) when [Au(CH2PMe3)2]Cl was allowed to stand in the presence of the ylide for seven days [Eq. (19)]. The 3IP-NMR spectrum showed only one signal, indicating that the two phosphorus centers were in identical environments, and the H-NMR spectrum exhibited two doublets with 2/(P—CH3) and 2J(P—CH2) having the same sign. Thus the symmetrical structure depicted in Eq. (19) was invoked, and the presence of two onium centers adjacent to the Au—C bonds was believed to stabilize this unlikely species. 

When definitely stabilized, the (EGDA)-Mo(VI) complex shows a doublet at 955-910 cm-1 which may be attributed to symmetric (Mo=0) the antisymmetric mode was not detected. The appearance of the symmetric Stretching-mode is consistent with a cis disposition of two terminal Mo=0 bonds (ref. 8). 

Phosphenium ions can also be stabilized by intramolecular coordination to a Lewis base. In ion 294, which was prepared by hydride abstraction739 [Eq. (4.177)], intramolecular bis-coordination exists. The31P NMR spectrum of the corresponding P—H derivative740 exhibits one doublet at 831P 37.6 (JP N = 243 Hz). The X-ray structure, which shows no interaction between the cation and the hexafluorophosphate anion, clearly demonstrates an ionic structure. Both arms are coordinated to the phosphorus center. The N—P distances are 2.082 and 2.068 A, which are longer than the N—P o-bond (1.769 A) but significantly shorter than the sum of the two van der... 

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