Complex sentence: Sullivan also organized a group of patrons of the Indianapolis Museum of Art who called themselves the Gamboliers; these patrons donated modest sums toward the purchase of works chosen by Sullivan which were then given in the group's name.
Split into simpler sentences: Sullivan also organized a group of patrons of the Indianapolis Museum of Art who called themselves the Gamboliers. They donated modest sums toward the purchase of works chosen by Sullivan which were then given in the group's name.