| Popis: |
The heat capacity Cp of the salt nitrosyl tetrafluoroborate, NOBF4, has been measured from 10 to 304 K, and that of potassium tetrafluoroborate from 9 to 295 K. The heat capacity–temperature curve of the nitrosyl compound has a λ‐type anomaly with Cp reaching a maximum at ∼67 K, and with an associated entropy gain estimated at 0.54R. Using Cp of the potassium salt as a reference, it appears that just above the λ point Cp of the nitrosyl salt once more starts to rise anomalously. The two‐dimensional librational or rotational movement of the nitrosyl ion is probably that of a restricted rotator in a somewhat unsymmetrical potential field, and admittedly it is difficult to estimate reliably the contribution to Cp from this mode of motion. Nevertheless, the total heat capacity of the nitrosyl salt for at least 200 K is such that it seems certain that it embodies a component reflecting the gradual gain by the nitrosyl ion of orientational disorder. We estimate that the total configurational entropy acquired on... |
Plný text