Atmospheric CO 2 fixation by a basic reaction mixture of [Ni II (3-MeOsaltn)(H 2 O) 2 ] and Gd III (NO 3 ) 3 ·6H 2 O gave a carbonate-bridged tetranuclear Ni II 2 Gd III 2 complex, (μ 4 -CO 3 ) 2 [Ni II (3-MeOsaltn)(MeOH)Gd III (NO 3 )] 2 ·H 2 O, where 3-MeOsaltn denotes N,N′-bis(3‐methoxy-2-oxybenzylidene)-1,3-propanediaminato. The tetranuclear structure possessing an inversion center can be described as two [Ni II Gd III ] binuclear units bridged by two carbonate CO 3 2− ions: two oxygen atoms of the carbonate ion bridge the high-spin Ni II and Gd III ions of a binuclear unit and the remaining oxygen atom of the carbonate ion coordinates to a Gd III ion of the adjacent binuclear unit. The temperature-dependent magnetic susceptibilities, from 1.9 to 300K, follow the Curie–Weiss equation of χ M T=C/(T−θ) with θ=+2.3K and C=18.24cm 3 Kmol −1 , suggesting a ferromagnetic interaction. The magnetic data were well reproduced assuming two independent [Ni II –Gd III ] binuclear units with the parameters of J(Ni–Gd)=+1.2cm −1 and D=+2.1cm −1 .