Three chromium(III) complexes with mixed amino acid ligands: (l‐cysteinato)(l‐histidinato)chromium(III) 3.5‐hydrate, (l‐aspartato)(l‐histidinato)chromium(III) 1.5‐hydrate and bis(dl‐histidinato)chromium(III) chloride 4.2‐hydrate