where tacn (pronounce tack-en) stands for 1,4,7-Triazacyclononane and is the distorted ring with three N H units (small, gray - tiny, white). Carbon atoms are (small, white) and come in twos, sharing a double bond. Fe is (large, gray) and O is (small, black). All Fe are Fe3+, high spin state, . The total effective spin, in the depicted ground state configuration is therefore
For µSR purposes it does have three unsaturated bonds per tacn, i.e. eighteen in all.
Certain to produce radicals: by eye I would count the following isomers:
If the symmetry is lower than I assumed there are certainly two mirror planes (horizontal and vertical, so that at most there are six isomes with multiplicity: 4 4 4 2 2 2