Is a landlord obligated to deposit tenant's security in an interest-bearing account upon the expiration of the tenant's option to purchase?

The landlord violated the express provisions of the lease by failing to deposit tenant's security in an interest-bearing account upon the expiration of the tenant's option to purchase. However, inasmuch as there is no evidence of commingling, the landlord does not forfeit the security (Matter of Perfection Technical Services Press, Inc., 22 A.D.2d 352, 256 N.Y.S.2d 166, aff'd 18 N.Y.2d 644, 273 N.Y.S.2d 71, 219 N.E.2d 424; Purfield v. Kathrane, 73 Misc.2d 194, 341 N.Y.S.2d 376). On the other hand, the tenant is entitled to set off the amount of legal interest due against the landlord's claim for rent.