Layered materials composed of metal-alkanethiolate units have been synthesized and characterized. The self- assembly occurs at the interface between a metal-ion-containing aqueous phase and an alkanethiol-containing organic phase. Key features of the structure have been determined from X-ray diffraction and infrared spectroscopy measurements. The highly ordered bilayers are characterized by tilted, all- trans alkyl chains. A new model for the in- plane structure has been presented, which is based on a hexagonal arrangement of metal atoms in the central plane.