An alternative interpretation of the “anomalous” positive g∥-shift observed for NH4I: Cu2+

It is shown that the positive g_∥-shift observed for two centers in NH₄I : Cu²⁺ with compressed octahedral geometry can be reasonably understood within a molecular orbital picture for a true C_4v complex. Following this explanation, which discards the vibronic admixture mechanism proposed by Chand and Upreti, the positive g_∥ - g₀ value arises from a charge-transfer contribution to g_∥ - g₀ similar to that of d⁷ ions in strong-field situations.