Mononitrosyliron compounds (MNICs) of the Enemark-Feltham {FeNO} 7 type divide into a dublet (S = 1/2) and a quartet (S = 3/2) spin variant. The latter relies on weak-field coligands such as aminecarboxylates. Aqua-only co-ligation appears to exist in the long-known 'brown-ring' [Fe(H 2 O) 5 (NO)] 2+ cation which was prepared originally from ferrous salts and NO in sulfuric acid. A chloride variant of this species, the green [FeCl 3 (NO)] − ion, was first prepared analoguosly by using hydrochloric instead of sulfuric acid. As a tetrahedral species, it is the simple prototype of sulfur-bonded {FeNO} 7 (S = 3/2) MNICs of biological significance. Though being investigated for more than a century, neither clean preparative routes nor reliable structural parameters were available for the [FeCl 3 (NO)] − ion and related species such as the [FeCl 2 (NO) 2 ] − ion, a prototypical dinitrosyliron species (a 'DNIC'). In this work, both issues have been resolved. In addition, we report on a computational study on the ground-and excited-state properties including an assignment of the chromophoric transitions. Photoinduced metastable isomers were characterised in a combined experimental and computational approach which resulted in the confirmation of a single photoinduced linkage isomer of the paramagnetic nitrosyl-metal coordination entity.