Spin units

The basic components of the solid state spectrometer are the same as the solution-phase instrument data system, pulse programmer, observe and decoupler transmitters, magnetic system, and probes. In addition, high-power amplifiers are required for the two transmitters and a pneumatic spinning unit to achieve the necessary spin rates for MAS. Normally, the observe transmitter for 13C work requires broadband amplification of approximately 400 W of power for a 5.87-T, 250-MHz instrument. The amplifier should have triggering capabilities so that only the radiofrequency (rf) pulse is amplified. This will minimize noise contributions to the measured spectrum. So that the Hartmann-Hahn condition may be achieved, the decoupler amplifier must produce an rf signal at one-fourth the power level of the observe channel for carbon work. 

According to the vendor, using the ROTAR system and Bio-Spin technology costs approximately 22 to 30 per ton of untreated material. The ROTAR system is a small-scale Bio-Spin unit (D22467J). 

Magnetism as a consequence of exchange interactions between spin units 114... 

Assembly of organic spin units into polyspin oligomers and polymers 116... 

Magnetic materials composed of organic molecular spin units - a brief... 

Although many naturally occurring and designed materials are magnetic due to incorporation of paramagnetic ions or metal atoms, organic-based magnets are composed of molecules or (in the case of polymers) monomeric repeat units. Each molecule must have net unpaired electron spin density. Several example radical spin units are shown in Scheme 1. The unpaired spin may be... 

Scheme 1 Example organic radical spin units. ...

So long as there are no or limited interspin exchange interactions in a system, M increases with H until all spins are aligned with the external field to the maximum extent allowed by thermal motion. Thus, at higher fields, M plateaus and is said to be saturated (Msat). The value of Msat can be used to determine S, so long as one knows molar mass of the individual spin units to get Msat in emu/ mol by the following equation ... 

In general, the Curie constant C from the slope of l/x versus Tcan be used with the above equation to find the spin quantum number S of the spin carriers, assuming g 2 for organic spin units. The // T criterion for the Curie law is readily achieved in an external field of 1000 Oe at 1 K for calibration, 10,000 Oe (1 T) — 1 cm-1 — 1.33 cal/mol 5.6 J/mol — 0.7 K. If there is a weak, generalized interaction between spin units, one can apply a mean-field, generalized correction, 9 (the Weiss constant), to the Curie law to get the so-called Curie-Weiss law as follows in Equation (4) ... 

We now turn to considering exchange linkage between spin units in a more general fashion, as a transition from organic radical spin units to organic magnetic materials. 

Lahti and Ichimura described oligo-cluster models of polyphenoxyl systems (e.g., in Fig. 11) in semiempirical MO-CI computational studies of potential experimental targets.111 Their findings indicated that such systems would maintain interspin exchange even with moderate amounts of torsion of their pendant spin units or main conjugated chain units, up to about 30°. 

Fig. 16 Rajca s multipath, hyperbranched, main-chain spin unit polyradical architecture.

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