Is zakat obligatory on money I loaned to my father—money that exceeds the nisab—provided that I will retrieve it in the form of real estate?

Zakat on a debt is obligatory at the end of each year (hawl). It is permissible for the creditor to delay paying the zakat until he receives the money, then he pays zakat for the past years. The intention to reconcile with the father by taking something from his property in exchange for the debt does not prevent the obligation of zakat on the loaned money for the past years, because the zakat has become a fixed liability on you upon the passing of the hawl. However, if you reconcile with him by taking something non-zakat-eligible from his properties, the zakat will be waived for you in the coming years.