Y is an anionic or nonanionic ligand group bonded to Z and M comprising nitrogen, phosphorus, oxygen or sulfur and having {TAIL ~ up to 20 non hydrogen atoms}, optionally Y and Z together form {HEAD ~ a fused ring system} 
Y is an anionic or nonanionic ligand group bonded to Z and M comprising nitrogen , phosphorus , oxygen or sulfur and having { TAIL ~ up to 20 non hydrogen atoms } , optionally Y and Z together form { HEAD ~ a fused ring system }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD