lien rights

It depends on who you had a contract with. If you had a contract for work with the old owners before they sold the property, then generally you can still record a lien against the property. The new owner would have a claim against the original owner for reimbursement, but typically that would not be your problem - if all required notices were given and the lien is timely filed, then you're free to record your mechanic's lien. 

If you had a contract with the new owners and did the work under the new ownership, then you'd treat it as any regular mechanic's lien - the prior owner being a tenant is irrelevant. 

If you entered into a contract with the old owner (now tenants) even though the property was owned by a new owner, then typically any mechanic's lien would only attach to the tenant's leasehold interest in the property. However, the lien may attach to the owner's interest in the property if the owner knew the work was taking place (they approved it, knew of it, or the lease gives the tenant permission to order the type of work) AND the owner fails to post and record a Notice of Nonresponsibility.

Even if you are unable to record a lien, you should have available to you standard breach of contract litigation rights. So, unless you were unreasonable in performing the work (you did so without permission, for example), you should be able to file suit against a combination of the owner (whose property has benefitted) and the party that authorized the work (breach of contract, misrepresentation, etc.)