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In octahedral Cr(III) complexes, the lowest excited doublets are more reactive than the (equiconfigurational) ground state but less than the lowest excited quartets. Moreover, the spatially degenerate doublets are characterized by negligible Jahn-Teller interactions while the degenerate quartets are subject to a large Jahn-Teller energy splitting. Both effects are shown to be related to certain specific features of half-filled shell states.

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The substitution photostereochemistry of octahedral d1 2345 complexes is analyzed on the example of cis-and trans-disubstituted Ru(III) amines. On the basis of a dissociative mechanism, state correlation diagrams suggest important differences between d5 and d6 photochemistry. The absence of thermally equilibrated excited states in the five-coordinated fragment may be a specific d5 feature.

Most irreducible-matrix representations in point-group symmetries can adopt monomial form. In that case all representational matrices have only one nonzero element in each row and column. The so-obtained standard basis choice contrasts with the conventional Wigner-Racah option. Monomial representations give rise to interesting properties of the corresponding Clebsch-Gordan series: All coupling coefficients are equal in absolute value and a natural intrinsic multiplicity separation is obtained. The concept is also useful in reaching a consistent solution of the multiplicity problem in the reduction of direct products, involving the fourfold U' representation of the octahedral spinor group. Several tables of basis transformations and coupling coefficients in octahedral and icosahedral symmetries are included.