The ring current model of the pentaprismane molecule

Three-dimensional models of the quantum-mechanical current density J(B), induced in the electron cloud of the C10H10 pentaprismane molecule by a magnetic field B applied along the C-5 (a C-2) symmetry axis, orthogonal to the pentagonal (a rectangular) face, and denoted by B-parallel to (B-perpendicular to), have been constructed. Predictions of near Hartree-Fock quality are reported for the diagonal components of magnetic tensors, magnetizability (xi), nuclear shielding of carbon (sigma(C)) and hydrogen (sigma(H)), and virtual shielding at the center of mass (sigma(CM)). The complicated spatial features of the induced electronic current-density field have been rationalized and compactly described via stagnation graphs that elucidate the details of its topological structure. A representation of JB is obtained by three-dimensional perspective plots and by planar maps visualizing phase portraits of electron flow in a series of molecular domains. Both streamline J(B)/|J(B)| and modulus |J(B)| are analyzed. These graphic tools illustrate the competition between diatropic and paratropic regimes which determine the magnitude of various components of magnetizability and magnetic shielding of hydrogen and carbon nuclei. Shielding density maps show that the differential Biot-Savart law explains magnetic shielding at hydrogen and carbon nuclei, and virtual shielding at ring and cage centers. Similarities and/or contrasting ring current effects on magnetotropicity are discussed by a comparison with triprismane C6H6 and cubane C8H8.