Pascal’s constant

Another additive term in the magnetic susceptibility arises from the temperature-independent core diamagnetism of all the ions in a solid. For YBa2Cu307 the core diamagnetism is approximately -2 x 10 7 based on a calculation using Pascal s constants (9). This small negative contribution serves to reduce the total susceptibility. A third possible contribution arises from Van Vleck paramagnetism (10) caused by excited states in the atoms of the... 

Fine crystalline and polymer samples were mounted in a capsule and measured on a Quantum Design MPMS-5S SQUID susceptometer at 5000 G. Corrections for the diamagnetic contribution were made using Pascal s constants. 

TABLE 1 Pascal s constants Xi for diamagnetic susceptibility" (units of 10-" mol )... 

The value of 0 0 is obtained from the intercept of the plot. Compare this value of the diamagnetic susceptibility of the solute with that estimated from Pascal s constants in Table 1. For single-temperature measurements, estimates of the latter type should be used to obtain for use in Eq. (14). 

General All starting materials were of analytical grade. Elemental analyses (C, H, N) were performed on a Perkin-Elmer 240 analyser. IR spectra were recorded on a Shimadzu IR-408 spectrometer as KBr pellets. Variable-temperature magnetic susceptibilities were measured on a Quantum Design MPMS-7 SQUID magnetometer. Diamagnetic corrections were made with Pascal s constants for all the constituent atoms. 

Satisfactory agreement was noted between the observed values for core diamagnetism (A) in Table I and those estimated from Pascal s constants for the PDA repeat unit. The data for poly-DCHBrg indicate a concentration of spin 1/2 species of ca 10 per mole. 

Tests showed that M s secured via (17) were as accurate as others determined cryoscopically. The method is obviously generally applicable to all liquid polymers for which the structural pattern is known and is uniformly repeated throughout the macro-chain as x becomes larger the observable differences between the L s and d s of molecules with x and x +1 become smaller, and precision in M is thereby reduced. An analogous proposal by Farquharson (1936) to use Pascal s constants... 

A structure determination of the other mononuclear chelate, Ni[H2-(BAA)2en], was deemed not necessary because of its unambiguous characterization by spectral and magnetic measurements. The visible spectrum of Ni[H2(BAA)oen] is essentially identical to that of Ni(Acac)2cn which is known to contain square planar Ni(II). The IR spectrum contains an intense unchelated carbonyl bond at 1700 cm which indicates that the nickel atom is coordinated to two nitrogens and two oxygens. In addition, Ni[H2(BAA)2en] is diamagnetic with Xg obs. = —266 X 10" cgs while Xg calculated from Pascal s constants is —246 X 10 cgs, which is further proof of square planar geometry about the Ni. 

The effect will depend on the number and distribution of electrons, and is therefore roughly constant for a given element. The approximate molar diamagnetic susceptibility y can be calculated by taking the tabulated contributions from the known values for each element, called Pascal s constants (Table 1), and adding them up, e.g.,... 

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