As used herein, a paramagnetic metal ion is selected from {HEAD ~ a group} consisting of Gd, Mn, Mn, Fe, Cr, Cu, Co, Ni, Dy, Tb, {TAIL ~ Ho}, Er, Eu, and Nd 
consisting of
As used herein , a paramagnetic metal ion is selected from { HEAD ~ a group } consisting of Gd , Mn , Mn , Fe , Cr , Cu , Co , Ni , Dy , Tb , { TAIL ~ Ho } , Er , Eu , and Nd
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL 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 OTH OTH OTH OTH OTH OTH OTH