Understanding Magnetic Susceptibility and Dipolar Interactions in Bulk Materials

1. Shape dependent demagnetization factor values 2 A˚ equal spacing Benzene Molecule & Its magnetic moment Further a lattice summation over the single crystalline ordered molecules extends to induced fields in bulk materials {χM . (1-3.COS2θ)}/(RM)3 Illustration for a single molecule contribution Extension to several molecules by summation of each molecular-contribution Figure-1. The magnetic dipole model; At the molecule the external Magnetic field induces magnetic moment – as seen in the figure above – which is a diamagnetic moment, at the centre of the charge cloud. In turn, this Induced Moment causes secondary field in the neighborhood. A point in the neighborhood is specified by the radius vector R and the angle θ.

2. When an external magnetic field is applied, the net circulation effect at the boundary of charge cloud is altered + The extent to which the charge cloud get influenced by the presence of an external field, and hence get altered in their charge cloud charactristics is called the Magnetic Susceptibility and is represented by the Greek letter (symbol) The magnetic susceptibility caused changes are said to induce a magnetic moment in the system which is given the symbol + + + + + QM Molecular Orbital Calculations: intra molecular shielding Dipolar secondary fields: inter molecular

3. ISC 98-104 ISC96 2009 - NEHU Shillong

4. Even while Calculating intermolecular contributions in crystal lattices, it was necessary to fragment the molecules at crystal sites and get susceptibility tensor values for molecular fragments. As this effort proved fruitful, it was necessary also to ensure that this is a durable method and not any fortuitous result providing a break-through. The report (as early as in 1974) about atom and bond susceptibilities independently yielded experimental shielding tensor value and atom susceptibilities could not be combined to get the corresponding bond susceptibilities. Thus the interpretation of HR PMR studies on organic molecular single crystal specimen did provide an evidence that a comprehension of the inconsistency is necessary as it seems to pave the way for interpretations of the induced fields and susceptibility values at intra molecular frameworks more durably.

5. Absolute Shielding Values Experimentally measured values Theoretical Values by QM calculations Spatially resolved induced field values Property over total Molecular extent For a chemical compound, the experimental methods are known for measuring magnetic susceptibilitties For a chemical compound, the experimental PMR spectra can be measured Calculations using Magnetic Point-Dipole model. Consistent spatial resolution for magnetic susceptibility ISC101 and ISC102 Papers entailed the details of the scheme as depicted in this slide http://saravamudhan.tripod.com/#flygare Magnetic Susceptibility data for molecules, functional groups, bonded regions & atoms Molecule is fragmented for assigning susceptibility for the fargments which when appropriately added yield the Molrcular susceptibility Calculating with the magnetic dipole model is a parallel independent way to relate experimentally measured quantity to the theoretically calculated values

6. Calculating Intra-molecular Proton Shielding Tensors Using Magnetic Dipole model; Possible Procedures and Prerequisites ISC101- Year 2014 Perspectives On Charge Circulation, Susceptibility, Induced Fields and NMR Chemical Shifts ISC102 – Year 2015 Molecular Susceptibility Tensor And The Susceptibility Tensor For Molecular Fragments ISC103 – Year 2016 Classical dipole model and the Abinitio QM method for Calculation of Magnetic Shielding in Molecules ISC104 – Year2017