Abstract: The present invention provides a method for binding gaseous molecules, the method comprising contacting gases comprising the gaseous molecules with trivalent metal complexes. Typically, the gaseous molecules comprise polar molecules of greenhouse gases, especially the oxides of carbon, nitrogen and sulphur. Preferably, the trivalent metal complexes comprise complexes of actinide metals, most preferably uranium. The method is particularly useful in the removal of so-called greenhouse gases from the atmosphere, and is therefore of potentially very great value environmentally. The invention also provides trivalent metal complexes comprising sandwich complexes of trivalent metals selected from transition metals and actinide metals, the complexes comprising two ligands selected from pentalenyl, indenyl, cyclopentadienyl and cyclooctatetraene ligands. The invention further provides a method for the preparation of the trivalent metal complexes.