In my Krause (2010!) Iran doesn't go beyond 2007, and the last denomination was 500 rials. (But in 2007 they switched from Cu-Ni to Alum-Bronze.) So someone else would have to give you KM# (you may have to wait for it couple of years).
The 100 rials are minted in aluminum-bronze with a diameter of just slightly smaller than 23mm and weighs in little more than 1 gram lighter. So, I would doubt it is aluminum-bronze. A cupro-nickel coin, however, has the specifications you give (23mm@5.85g). The SH1388(2009) 1000 rial is designated KM#1272 in cupro-nickel with your size/weight specifications. Perhaps Krause just hasn't received verification of the SH1387 dated coin.
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