Moscow is the capital. Actually there are several centres so far, Saint Petersburg is one, probably not very "economic", but undoubtedly the most cultural and political centre. There are cities which have more than 1 mln people population each and can be called "economic centres" as well.
Volgograd, formerly Stalingrad, was one of the major cultural centres before the fall of the USSR. Now the Economic centre is moskva while culture is mostly St. Petersburg.