| 556 / | HD | ORGANIC COMPOUNDS -- PART OF THE CLASS 532-570 SERIES |
| * | DD | ORGANIC COMPOUNDS (Class 532, Subclass 1) {3} |
| 1 | DF | .~ HEAVY METAL CONTAINING (e.g., Ga, In or T1, etc.) {19} |
| 138 | | .~.~ Iron, cobalt, or nickel containing (Fe, Co, or Ni) {3} |
| 139 | DF | .~.~.~> Sulfur double bonded directly to chalcogen |
| 140 | DF | .~.~.~> Carbon bonded directly to the metal {2} |
| 146 | DF | .~.~.~> Chalcogen bonded directly to the metal {2} |