1. Single atoms act as central nuclei, around which are arranged a definite number of other atoms. coordination number. the most important Coordination numbers :3, 4, 6 and 8, the number 6 occurring especially often 40 Series of optically-active complexes with 2. Optically-active isomers of the complexes octahedral symmetry were separated in optically-active forms.1. Single atoms act as central nuclei, around which are arranged a definite number of other atoms, coordination number. The most important Coordination numbers : 3, 4, 6 and 8, the number 6 occurring especially often. 2. Optically-active isomers of the complexes , 40 series of optically-active complexes with octahedral symmetry were separated in optically-active forms