Five neutral platinum-based macrocycles incorporating cyclic oxocarbondianions, squarate and croconate and their acyclic analogue, oxalate, have been synthesized in 90-95% yield via self-assembly. The combination of the diplatinum molecular clip with all three dianions afforded molecular rectangles, whereas a platinum-based 60 degrees acceptor unit produced a supramolecular rhomboid with croconate ion but a triangle with squarate ion. In all cases, multinuclear NMR spectra were consistent with the formation of single highly symmetrical species. The three rectanglular and the rhomboid assemblies were characterized by single-crystal X-ray crystallography. The triangular species was characterized by FAB mass spectrometry.