Treatment of UO 2 X 2 (X=OAc, Cl, NO 3 ) with 1mol equiv of (py) 2 CO in THF afforded the adducts [UO 2 X 2 {(py) 2 CO}] in almost quantitative yields. The same reactions in MeOH, in the presence of NEt 3 for X=Cl and NO 3 , gave yellow crystals of [(UO 2 X) 2 {μ-(py) 2 C(OMe)O} 2 ]·MeOH (X=OAc, 1·MeOH and X=Cl, 2·MeOH) and [{UO 2 (NO 3 )} 2 {μ-(py) 2 C(OMe)O} 2 ] (3). Reactions of UO 2 X 2 (X=OAc, Cl) with 2mol equiv of (py) 2 CO and NEt 3 in MeOH or further treatment of 1 and 2 with 1mol equiv of (py) 2 CO and NEt 3 afforded the methoxide derivative [{UO 2 (OMe)} 2 {μ-(py) 2 C(OMe)O} 2 ] (4), while UO 2 (NO 3 ) 2 was transformed into [{UO 2 (NO 3 )}{UO 2 (OH)}{μ-(py) 2 C(OMe)O} 2 ] (5). In these first structurally characterized actinide compounds with a (py) 2 CO-based ligand, the uranium atoms are located at the center of pentagonal (X=Cl and OMe) or hexagonal (X=OAc and NO 3 ) bipyramids sharing one edge defined by the μ-alkoxo oxygen atoms. Crystals of [{UO 2 (OMe)} 2 {μ-(py) 2 C(OMe)O} 2 ]·[(UO 2 ) 4 {μ 2 -(py) 2 C(OMe)O} 2 (μ 2 -OAc) 2 (μ 3 -O) 2 (MeOH) 2 ]·H 2 O (6·H 2 O) were serendipitously obtained in one experiment with [UO 2 (OAc) 2 (H 2 O) 2 ] and (py) 2 CO.