Tetrahydrofuran spin density

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) studies on frozen solutions of TDTA in tetrahydrofuran (THE) allowed estimates of its spin density distribution <2005JCD3838>. A comparison with that of TTTA <2001JMC1992> determined by similar methods shows that replacement of N of TTTA by isoelectronic C-H groups results in greater localization of spin density on the dithiazolyl ring. 

Interesting is a comparison of the volumes occupied by individual complexes in solution and in the solid state. The partial molal volumes can be obtained from precise measurements of the solution densities of the complexes as a function of concentration [177]. These values may be subsequently compared with the unit cell volumes per complex molecule derived from the crystal structure. For Fe[HB(pz)3]2, the apparent molal volume in tetrahydrofuran solution was determined as 340.9 em mol Taking into account that the complex in solution forms an equilibrium between 86% LS and 14% HS isomers and employing the volume difference between the two spin states AF° = 23.6 cm mol S the volume of the LS isomer was calculated as 337.6 cm mol This value agrees closely with the volume of 337.3 cm mol for the completely LS complex in solid Fe[HB(pz)3]2 [105]. 

The relaxation dynamics of junctions in polymer networks have not been well known until the advent of solid-state P NMR spin-lattice relaxation measurements in a series of poly(tetrahydrofuran) networks with tris(4-isocyanatophenyl)-thiophosphate junctions (Shi et al., 1993). The junction relaxation properties were studied in networks with molecular weights between crosslinks, Me, ranging from 250 to 2900. The dominant mechanism for P nuclear spin lattice relaxation times measured over a wide range of temperatures were fit satisfactorily by spectral density functions, 7([Pg.225]

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