While the appointment of Senator Hillary Clinton to Secretary of State appears to be an all but done deal, there are some legal scholars who believe that the move would be unconstitutional.The top federal executive level 1 pay increased from $186,600 to $191,300 during the 110th Congress so according to Article 1 Section 6, Hillary Clinton, or anyone else who served in the Senate or the House during that two years cannot be appointed to any civil office.
"Why? Because the Constitution forbids the appointment of members of Congress to administration jobs if the salary of the job they'd take was raised while they were in Congress," NBC's Pete Williams reports.
I'm sure this has happened before. The executive salaries are increased fairly often. In fact, it happened in 2001 when George W. Bush appointed John Ashcroft his Attorney General after Ashcroft served as a senator in the 106th Congress who increased the level 1 salaries from $161,200 to $166,700.
It was a nice try though.
ADDENDUM: After further review (and re-reading Section 6) I was wrong on John Ashcroft. If you remember, Ashcroft embarrassingly lost his re-election to a dead man so Bush didn't appoint him "during the Time for which he was elected".
But the example could be even better. Dick Cheney was appointed as Bush the First Loser's Secretary of Defense in 1989 after serving as a U.S. Representative in the 100th Congress and being re-elected to the 101st. I can't find level 1 salaries before 1990 though so I'm not sure if old Dickhead is a precedent or not.
ADDENDUM II: There are precedents;
Apparently, President Nixon ran into the same problem when he wanted to appoint Ohio's Republican Sen. William Saxbe as attorney general.
The solution back then, since dubbed the "Saxbe fix," was for Congress to pass another law (not without some outspoken dissent from Democratic senators, by the way) reducing the AG's pay so Saxbe wouldn't benefit financially from the higher salary he'd previously voted on.
Similar fixes occurred when President Jimmy Carter named Edmund Muskie secretary of State and H. Clinton's own husband Bill named Lloyd Bentsen to head Treasury.