Monogram is a stylized Cyrillic letter N (like Latin H), so it could be attributed to either Nicholas I or to his great-grandson, Nicholas II. There are no other Russian Tsars with name beginning with the letter N. However, the crown style would rather be associated with N I than with N II. This piece with the size of 21+ mm in diameter should not be related to a coin. Neither 1 kopek nor 1/2 kopek (some types ~ 21 mm) were made with this style of monogram+crown. However, the similar style presents on many medals and jetons of N I and N II. Moreover, many manufactures were licensed to produce medals, jetons, decorations etc with tsar's monograms, portraits and so on. So, I might suggest that this piece is related to a part of some kind of decoration, commemorative jeton or something similar to. Of course, I could be wrong.