Any lease of City property made by the Council for a period longer than five years shall be subject to referendum in the manner provided in Section 7.11 of the Charter relating to calling a referendum on ordinances. A petition calling for a referendum on a lease under this provision must be taken within 30 days from the date of the lease. If a proper petition has not been filed with the Clerk-Treasurer within 30 days from the date of the lease, the lease shall be valid and binding. Before the Council grants a lease, the lessee shall file an unconditional acceptance of the terms of the lease with the Clerk-Treasurer.