Complex sentence: In 1863 he offered his 2200 watercolors (half of which Belgian landscapes) to the Belgian government for 4000 franks; the offer was turned down because no one knew where to house the collection.
Split into simpler sentences: In 1863 he offered his 2200 watercolors (half of which were Belgian landscapes) to the Belgian government for 4000 franks. The offer was turned down because no one knew where to house the collection.