wherein R1 stands for at least one element selected from the group consisting of {HEAD ~ La}, Nd, {TAIL ~ Sm}, Eu and Gd and x and d are numbers as follows: 
wherein R1 stands for at least one element selected from the group consisting of { HEAD ~ La } , Nd , { TAIL ~ Sm } , Eu and Gd and x and d are numbers as follows :
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH