| http://www.w3.org/ns/prov#value | - (3) Preferably, the central element M is a metal, and is aluminum or tin. [0082] (4) In the above-mentioned chemical formula (1) and/or (2), preferably, at least any one or more groups of R1 through R8 are different from the other groups of R1 through R8. [0083] Hereafter, above-mentioned items (1) through (4) will be described. [0084] According to the inventors of the present invention and so for
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