Figure 1.

(a) Structures of 1, 1-d₄ and 1-d₁₈. (b) Ground-state quartet levels in high-spin, d⁷ complexes with $D_{4h}$ symmetry and D > 0; 2D′ = 2(D² + 3E²)^1/2; the quartet levels in 1 with lower symmetry: ${\varphi }_1=-a|-1/2>+b|+3/2>$; ${\varphi }_2=a|+1/2>–b|-3/2>$; ${\varphi }_3=b|+1/2>+a|-3/2>$; ${\varphi }_4=b|-1/2>+a|+3/2>$ where the mixing coefficients $a=\cos \beta$; $b=\sin \beta$; $\tan 2\beta =\surd 3\left(E/D\right)$ (SI of ref. 7). (c) Zeeman splitting of the Kramers doublets inside magnetic field B.