To treat them as charitable donations, you must have a letter of acknowledgement from the organization (it does not have to attest to the value of the items, you'll use receipts for that),

And, the items have to become the property of the organization (you will not take them with you when you leave, and the organization could come by your desk and say "nice lamp, but I think that belongs in someone else's office".)

Alternatively, if you have expenses for your job (no matter who you work for) that are ordinary and customary for your type of work and are not reimbursed by the employer, you can take them as unreimbursed business expenses on form 2106. But this is subject to the 2% rule so the actual tax benefit will be limited, if you can claim it at all.