Is it permissible to mortgage a commercial property for two amounts: one as a deposit that is returned upon the解除 of the mortgage, and the other a monthly amount that is not returned?

If the intent behind the loan is to benefit from the commercial property at a very low rent, then this is impermissible, because it is a loan that draws a benefit, and this is a forbidden form of usury (riba). Scheming around it by making the rent low does not change its ruling in any way, because deeds are judged by their intentions.