Maybe. If you had earned income in 2016 you can contribute up to $5,500 to an IRA (an extra $1,000) if you’re 50 or over. Your lump-sum leave payment is not considered earned income, though it is taxable. If your earned income is less than the amount you can contribute, you can contribute up to the amount of your earned income. TSP rules preclude your rolling over a Roth IRA into the Roth TSP.
You are allowed to contribute to a traditional deductible IRA if your income is below the levels specified in IRS Publication 590-A. It doesn’t matter that the contribution is coming from your lump-sum leave payment. Then you could roll the traditional deductible IRA into the traditional balance in your TSP.