Weak/strong/intermediate ligand field strength dictates the high-spin/low-spin/spin crossover mechanism in any given complex. This correlates to the number of lone electrons within a complex. This subsequently is correlated to the explore the strength of attraction the sample felt with respect to magnet. Spin only magnetic moment for first row transition elements/lighter elements of the periodic table changes to spin-orbit magnetic moment owing to the incorporation of relativistic effects associated with the heavier elements in the periodic table.Anomalous magnetic moment may also arise when a particular complex interacts with a coordinating solvent. Van Vleck equation has been deduced in order to gain deeper insights into the magnetic susceptibilities. Magnetic susceptibilities are dependent of molecular orientation with respect to the applied magnetic field; i.e. anisotropic in nature.Gyromagnetic tensor (g) values defined by magnetic susceptibility(Χ) measurements, best measured by EPR spectroscopy and most importantly anisotropic in nature.

When electronic spin (S)>1/2(i.e. more than one unpaired electron), the coupling of the ground state with excited states via spin-orbit coupling can also result in partially removing the degeneracy of the MS states in zero-field. The separation of the MS states in zero-field is the zero-field splitting (D). In magnetic studies this is often referred to as the single-ion anisotropy.Sign of D can be negative or positive depending upon the energy of the m

If the two paramagnetic centres A and B interact then the local spins SA and SB are not good quantum numbers for the system. The ions are said to be magnetically coupled, or are undergoing magnetic exchange. This exchange is described by a spin-Hamiltonian, which involves only spin operators and allows the wavefunctions (energy levels) of the system to be expressed in terms of spin functions only. Using the Bleaney-Bowers equation we can predict the behaviour of magnetic susceptibility and temperature for ferromagnetic (positive J) and antiferromagnetic (negative J) exchange interactions.

For antiferromagnetic exchange product of susceptibility and temprature(ΧT) decreases continuously with T while for ferromagnetic exchange ΧT increases on cooling, reaching a plateau at low temperatures (diamagnetic excited state is fully depopulated), i.e. Curie Law at low T with ΧT characteristic of the ground spin state.

Everything above concerns the “classical”, macroscopic, magnetism, at our scale, with various potential applications. We have crossed the quantum world towards transition to the macroscopic one, have seen the application of the theory, and taken the rigorous formula to the dream. It is a field persistently under development which is of essential interest not only in small, with “nano” but also with the complex. At a time when a Japanese Nobel laureate in Chemistry asserted that the synthesis of any molecule is now within reach of the chemist, the challenge was to conceive and synthesise increasingly complex systems in order to reach the requirements. These systems are not required to have only one property or function, but several functions: it is the world of multipurpose materials. These functions can exist alongside each other (magnetism and transparency) or they can interact with each other in order to create and highlight new properties.