Calculating nominal GDP
There is no need to complicate things here - just try to find annual exchange rate used by IMF. Worldbank's data are here. LCU stands for Local Currency UnitsYou may see a drop of Rub/$ rate from 31.84 to 38.38. (Drop of Ruble, of course.)
National statistics provides input figures for international accounts. According to Rosstat, Russian nominal GDP grew in the Y2014: 


Y2013 - 66,190 bil. Rub, 
Y2014 - 71,406 bil. Rub. 



Using  NGDP dollar evaluation from your post, annual exchange rate for Y2013 is 31.5 Rub/$; in Y2014 rate is 34.7 Rub/$, which makes some sense. But indeed Rub/$ rate was somewhat closer to 38.5 (see here). So, IMF figure for the Y2014 from your wiki reference seems to be more correct: bil. $1,857,461 for Russian NGDP. (do not forget about Crimea correction to appreciate the difference).
So, in fact Russian nominal GDP did drop significantly in current dollar terms in the Y2014. 
Imho, PPP is not applicable for your question as Russian GDP by PPP is of different magnitude.