Is it permissible to give charity with the intention of facilitating marriage, and is there any Shar'i basis for that?

It is desirable to seek intercession through charity before the Istisqa (rain-seeking) prayer, to bring good and repel evil. Charity is a benevolence that brings Allah’s mercy. Charity has a wondrous effect in repelling affliction, even if it comes from an immoral person or a disbeliever; this is a known fact confirmed by experience. It is also advisable to strive in acts of obedience, increase supplication, seek refuge in Allah, and repent to Him.