 Leopold Clement 's younger brother , Francis Stephen , was invited to Vienna . Even though Francis Stephen was his favourite candidate for Maria Theresa 's hand , the Emperor considered other possibilities . Religious differences prevented him from arranging his daughter 's marriage to the Calvinist prince Frederick of Prussia . In 1725 , he betrothed her to Charles of Spain and her sister , Maria Anna , to Philip of Spain . However , other European powers compelled him to renounce the pact he had made with the Queen of Spain , Elisabeth Farnese , as the marriage of heirs to the thrones of Spain and Austria would have destroyed the European balance of power . Maria Theresa , who had become close to Francis Stephen , was relieved . 
