prov:value
| - of the formula I ##STR21## in which R1 and R2 are identical or different and are a hydrogen atom, a C1 -C10 -alkyl group, a C1 -C10 -alkoxy group, a C6 -C10 -aryl group, a C6 -C10 -aryloxy group, a C2 -C10 -alkenyl group, a C7 -C40 -arylalkyl group, a C7 -C40 -alkylaryl group, a C8 -C40 -arylalkenyl group or a halogen atom,R7 is ##STR22## ???BR11, ???AlR11, --Ge--, --Sn, --O--, --S--, ???SO, ???SO
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