BIFUNCTIONAL MODEL COMPLEXES ACTIVE IN CARBON-DIOXIDE FIXATION - SYNTHESIS AND X-RAY STRUCTURE OF BIMETALLIC COBALT(I) ALKALI CATION SCHIFF BASE COMPLEXES

Reduction of (N, N‘-ethylenebis(salicylideniminato))cobalt(II), Co(salen), with lithium and sodium metals in tetrahydrofuran, THF, affords the bimetallic systems, which are active in carbon dioxide fixation, [(Co(salen))NaTHF] and [(Co(salen))Li(THF)15]. The structures of these complexes have been solved by single-crystal X-ray diffraction methods. Both of them contain a diamagnetic cobalt(I) in a slightly distorted square-planar coordination geometry due to a salen ligand which coordinates the alkali cation through the oxygen atoms. [(Co(salen))NaTHF] crystallizes in the orthorhombic space group P21212 with lattice parameters a - 7.416 (2) Å, b = 21.848 (9) Å, c = 11.639 (5) Å, and Z = 4. The structure has been solved by using 1579 observed reflections and refined to R = 0.030. The crystal structure consists of infinite chains, whose monomeric unit is [(Co(salen))2Na2(THF)2]. They can be described by distorted octahedra around Na+ sharing the opposite faces. Both THF and Co(salen) act, through the oxygen atoms, as bridging ligands between two adjacent sodium cations. [(Co(salen))Li(THF)1.5] is triclinic, space group P$$, with lattice parameters a = 16.892 (3) Å, b = 14.310 (3) Å, c = 10.899 (3) Å, α = 94.6 (2)°, β = 99.5 (2)°, γ = 122.3 (2)°, and Z = 2. The structure has been solved by direct methods and refined by least-squares methods to R = 0.089, for 2680 reflections. In the structure of [(Co(salen))Li(THF)1.5] there are two different molecular complexes, [(Co(salen))Li(THF)2] and [(Co(salen))2Li2(THF)2], in a 2:1 ratio. In both complexes, Li+ is in a distorted tetrahedral coordination. In the first complex, the four oxygens for the lithium coordination are provided by Co(salen), acting as a bidentate chelating ligand, and two THF molecules. In the centrosymmetric tetranuclear complex [(Co(salen))2Li2(THF)2] one of the THF oxygens of [(Co(salen))Li(THF)2] is replaced by a Co(salen) oxygen atom which bridges two lithium cations. © 1979, American Chemical Society. All rights reserved.