The molecular dynamics of cyclophosphazene inclusion compounds via (2)H nuclear magnetic resonance spectroscopy

The dynamic behavior of guest molecules in tris(o-phenylenedioxy)cyclotriphosphazene inclusion complexes is examined utilizing 2H. Nuclear Magnetic Resonance (NMR) spectroscopy. The guests of interest are n-C36D 74 and deuterated benzene. Several techniques have been used to study the mobility of guest molecules in inclusion complexes. However, 2 H NMR is the technique of choice, First of all, deuterium has a low natural abundance (about 0.016%). Additionally, 2H NMR yields an exceptionally high dynamic range over which motion can be measured. As a result, different types of motions can be identified readily and unambiguously. Moreover, information on anisotropic properties may be obtained through the analysis of solid state NMR lineshapes.;Quadrupole echo experiments were carried out at various temperatures on a homebuilt NMR spectrometer utilizing a 250 MHz superconducting magnet. The splitting of a Pake doublet in the 'absence' of motion is on the order of 128--150 kHz. However, the quadrupolar splitting of the Pake doublet for the tris(o-phenylenedioxy)cyclotriphosphazene-benzene-d 6 inclusion complex at room temperature is only 26.3 kHz (agreeing well with published data). Moreover, the tris(ophenylenedioxy)cyclotriphosphazene-C 36 D74 inclusion complex resulted in a superposition of three doublets since there are three types of deuterons. Relaxation results also verify that there are three distinct types of motion occurring in this complex. At room temperature, the quadrupolar splittings were 17 kHz, 60 kHz, and 30 kHz for the methyl, methylene, and penultimate deuterons, respectively. These splittings are narrower, by a factor of two, than the splittings of the lineshape for free n-C36D74. The narrowing of these lineshapes is a result of the motional averaging of the quadrupolar tensor. Variable temperature experiments, ranging from 70°C to --100°C, resulted in a slight narrowing of the lineshapes at higher temperatures and a slight broadening at cooler temperatures. However, motion still was not frozen out at --100°C.