Apologies, meant to write thanks for any help provided....
You can link one occurrence of clients to a second occurrence selecting any field in the one occurrence and linking it to any field inthe other occurrence. Then double click the relationship line to open a dialog where you change the = operator to the Cartesian join operater (X). This will match any record on your clients layout to all records in the second occurrence of the clients table.
You can then define this portal filter expression: IsEmpty ( Clients 2::Closed )
Use your name for the second occurrence of Clients in place of Clients 2.