Nixon was never impeached for anything. When it appeared likely that a House committee would vote to recommend that that the full House take up impeachment proceedings against Nixon; it was then that Nixon decided to resign. There was never any vote for impeachment for anything. There were never any articles of impeachment that were voted on by the House. Personally, I think Nixon should have stuck it out and fought the trumped up charges and witch-hunt of the leftist, self-righteous DemonRATs.
Google it. The House voted the article to impeach him.