To allow for a complete structural comparison of the series of systems of the type [C4O4] n-(n = 2, 4, 6) within the same aluminium coordination sphere, we also targeted the corresponding [C4O4] 2- (squarate) system. Such systems have been synthesized in the past by homologation of CO using metal centres (or combinations of metal centres) capable of effecting a two-electron reduction. In our hands, however, dimeric Al(II) systems such as (NON)Al-Al(NON) 51 do not react with CO under either thermal or photolytic conditions, presumably reflecting the stronger nature of the metalmetal bond, compared (for example) to dimeric Mg(I) reductants. For structural comparison, we therefore examined alternative synthetic approaches involving the reactions of pre-formed squarate salts M2[C4O4] with the readily available Al(III) iodide precursor (NON)AlI. In the event, (NON)Al(C4O4)Al(NON) ( ) is most easily accessed by combining the disilver salt of squaric acid, Ag2[C4O4] with (NON)AlI in Et2O. 5 has been characterized by standard spectroscopic and analytical methods, and by X-ray crystallography (Figure ). Its molecular structure features a planar carbocyclic [C4O4] 2-ligand bridging between the two aluminium centres. The carbon-containing fragment closely resembles those reported previously, .