MAGNETO-CHEMICAL STUDIES IN VALENCY. PART VI. BOND-TYPE AND STEREOCHEMISTRY OF FOUR-COORDINATED COPPER COMPLEXES

The magnetic susceptibility of a large number of copper compounds has been measured both at the room temperature and also, in a few cases, at low temperatures (-13° to —190°) for the purpose of θ-correction. From a comparison of the moment values, particularly after θ-correction, it has been shown that the 4-coordinated copper complexes can be divided into two groups: one with moment values lying between 1.72 and 1.82 Bohr and the other with values between 1.90 and 2.20 Bohr. The division, though not always a very sharp one, is still quite significant. It is, therefore, suggested that in the former the bond is homopolar of the dsp2 planar square type and in the latter it is either ionic or cova­lent of the tetrahedral sp9 or planar sp2d type. The lower moment value of the first group results from more or less complete quenching of the orbital moment of the single unpaired electron raised to the outermost 4.p level of the atom, where it is fully exposed to the electric field of the neighbouring atoms and ions, away from the nucleus screened by the co-ordinating electrons. This difference in moment value serves to distinguish between the two types of copper complexes, the penetration and the asso­ciated ones, though, in both, the central copper atom contains one unpaired electron. It is also signi­ficant to note that all those complexes with lower moment values (1.72-1.82) are either black, brown, red, greenish yellow or violet-blue, while others with higher moment values are green, blue or blue-violet. A relationship between the colour and the bond type or structure of the complex is thereby suggested, as in the corresponding nickel complexes