Among the halide and pseudohalide complexes, fluoro complexes of iron(III) are the most stable, with the colorless being the most stable in aqueous solution. Chloro complexes are less stable and favor tetrahedral coordination as in [FeCl4−; and [FeI4− are reduced easily to iron(II). Thiocyanate is a common test for the presence of iron(III) as it forms the blood-red Like manganese(II), most iron(III) complexes are high-spin, the exceptions being those with ligands that are high in the spectrochemical series such as cyanide. An example of a low-spin iron(III) complex is [Fe(CN)63−. The cyanide ligands may easily be detached in and hence this complex is poisonous, unlike the iron(II) complex [Fe(CN)64− found in Prussian blue, which does not release hydrogen cyanide except when dilute acids are added. Iron shows a great variety of electronic spin states, including every possible spin quantum number value for a d-block element from 0 (diamagnetic) to (5 unpaired electrons). This value is always half the number of unpaired electrons. Complexes with zero to two unpaired electrons are considered low-spin and those with four or five are considered high-spin.