This is actually a rather complicated question.  You mention that there are no assets being purchased, but you do not state was is actually being purchased.  Likely you meant that there are no tangible assets, but the purchase invovles intangible assets, which could be things like a client list, patents, trade secrets, etc.  Or possible it could be a non-compete agreement.

Intangibles can be amortized over 15 years, however you must evaluate if the intangible is "self created" which may be somewhat murky in a 50 / 50 partnership.

An attorney should definitely be involved in structuring this deal so that there is agreement on specifically what is being purchased for $200k, and what the treatment is.