Your Ex-wife most likely gets her own 1099-R for her portion of the distribution. So that means she's paying tax on it as a retirement distribution and doesn't have to also pay tax as alimony. So, you cannot deduct it as alimony. But, more importantly, if the share she gets is not included on your 1099-R, you can't deduct it because it has effectively already been deducted from the income you receive.
