COVALENT BONDING IN OCTAHEDRAL (MNCL6)4- AND TETRAHEDRAL (MNCL4)2- COMPLEXES

Chlorine ligand hyperfine structure has been observed in the EPR spectrum of the octahedral complex ion (MnCl6)4-, in dilute solution in a single crystal of K4CdCl6 at room temperature. From the isotropic and anisotropic components of the spectrum, it is estimated that f8 = 0.40%, and (fσ-f π) =3.9%, respectively. No chlorine ligand hyperfine structure is observed in the tetrahedral complex ion (MnCl4)2- introduced as an impurity in either [N(CH3)4 ] 2ZnCl4 or [(C6H6)8CH 3As]2ZnCl4. A substantial reduction in the manganese nuclear hyperfine coupling constant A2(Mn) is observed in both cases, however, A2(Mn) having the value -79.50±0.50 G for [N(CH3)4]2ZnCl4, and -79.30±0.50 G for [(C6H6)3CH 3As]2ZnCl4 compared to -86.40±0.40 G found for MnCl64- in K4CdCl6. The failure to observe ligand hyperfine interactions in the tetrahedral ion is discussed in terms of the shorter bond distance in the four coordinated compound and the increased importance of π bonding.