Diamagnetic Anisotropy Derived from Single Chemical Bonds in the Silicate Tetrahedral Networks

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The diamagnetic anisotropy (Δ χ )_DIA derived from the individual bonding orbitals of the silicate [TO₄] networks is estimated from the observed results on α-quartz [SiO₂], orthoclase [KAlSi₃O₈] and apophyllite [Ca₄KF(Si₄O₁₀)₂, 8H₂O]. The (Δ χ )_DIA value of individual chemical bond was estimated to be -3.5× 10^-30 emu/mol, the uniaxial principal axis being parallel to the bond direction. The calculated results indicate that the bond direction is the magnetically unstable axis. This result is compatible with the observed and calculated distributions of electron density for the T-O orbitals, which are preferentially spread in the direction off the bond direction.