Ligand Field Theory of Ni(II) Complexes. II. Electronic Spectra and Structure of Some Paramagnetic Chelates

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Abstract
An assignment of the observed absorption spectra is made for each of six paramagnetic Ni(II) chelates studied, based on the energy levels calculated for the Ni(II) ion from an electrostatic model of the complex. The best assignments, in each case, give reasonably good qualitative and quantitative agreement, explaining the number and relative intensities of the triplet‐triplet and triplet‐singlet transitions and giving maximum error of 30% when compared with the observed positions of maximum intensity. The consistency and relative significance of the values of the effective dipole moments used for the different coordinating oxygen and nitrogen atoms is demonstrated in several specific assignments. For the chelates of unknown structure and coordination, a comparison of various possible assignments enables structural predictions, while the chelates of known structures are given reasonable assignments with their appropriate configurations. The sensitivity of the assignments to the assumed structures allowed the general conclusion to be drawn that significantly better results are obtained if unequal effective dipole moments of different ligands are used, rather than one average value. For example, all six coordinated chelates with mixed ligands were given better assignments in tetragonal or trans‐planar symmetry than octahedral symmetry. It is felt that this study demonstrates the scope of the electrostatic model of the complex ion and justifies its use to explain and predict properties of the complex molecule associated with the central ion.