Polymer, composition, electrochromic element, dimming device, and display device

A polymer, comprising a complex in which compounds A represented by formula (1) are bound to at least one specific metal ion selected from the group consisting of a first metal ion having a coordination number of 4, a second metal ion having a coordination number of 6, and a third metal ion having coordination numbers of 4 and 6:

• BP1-L1-BP2 (1)
• wherein L1 represents a single bond or a divalent group, and BP1 and BP2 each independently represent a bipyridine derivative, which may be identical to or different from each other, provided that when at least one of hydrogen atoms bonded to carbon atoms of the bipyridine derivative is substituted with a monovalent group, the monovalent group does not include a pyridyl group, and
• wherein the complex is formed in such a manner that one of the BP1 and BP2 of one of the compounds A is bound to one of the BP1 and BP2 of another one of the compounds A via the specific metal ion, by which the compounds A are continuously bound to each other.