What is the validity of a marriage where the exchange is: 'I marry you to my female slave on the condition that you marry your daughter to me, and her freedom becomes the dower for your daughter'?'

Primary text

The marriage of the female slave is invalid according to the primary opinion of the madhhab because she was not given a dower other than the marriage of the contracting party's daughter. If a man marries his daughter on the condition that the freedom of a female slave is made her dower, the marriage is valid because the female slave is a proper subject for a dower.