prov:value
| - wherein R9 is a halogen atom or one or more kinds of organic groups selected from the group consisting of alkyl groups, aryl groups, alkoxy groups and acyloxy groups of 1 to 20 carbon atoms and a carbonyl group adjacent to an active methylene group, M is B, Mg, Al, Ca, Sn, Pb or a transition metal atom belonging to one of the 3A group to the 7A group, the 8 group, the 1B group and the 2B group in
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