Lanthanide-transition-metal carbonyl complexes: new [Co4(CO)11]2- clusters and lanthanide(II) isocarbonyl polymeric arrays

Two types of Ln(II)-Co(4) isocarbonyl polymeric arrays, (Et(2)O)(3)(-)(x)()(THF)(x)()LnCo(4)(CO)(11)]]( infinity ) (1-3; x = 0, 1) and (THF)(5)EuCo(4)(CO)(11)]]( infinity ) (4), were prepared and structurally characterized. Transmetalation involving Ln(0) and HgCo(CO)(4)](2) in Et(2)O yields (Et(2)O)(3)LnCo(4)(CO)(11)]]( infinity ) (1, Ln = Yb; 2, Ln = Eu). Dissolution of the solvent-separated ion pairs Ln(THF)(x)()]Co(CO)(4)](2) (Ln = Yb, x = 6; Ln = Eu) in Et(2)O affords (Et(2)O)(2)(THF)YbCo(4)(CO)(11)]]( infinity ) (3) and (THF)(5)EuCo(4)(CO)(11)]]( infinity ) (4). In these reactions, oxidation and condensation of the Co(CO)(4)](-) anions result in formation of the new tetrahedral cluster Co(4)(CO)(11)](2)(-). The two types of Ln(II)-Co(4) compounds contain different isomers of Co(4)(CO)(11)](2)(-), and, consequently, the structures of the infinite isocarbonyl networks are distinct. The cluster in (Et(2)O)(3)(-)(x)()(THF)(x)()LnCo(4)(CO)(11)]]( infinity ) (1-3) possesses pseudo C(3)(v)() symmetry (an apical Co, three basal Co atoms; one face-bridging, three edge-bridging, seven terminal carbonyls) and connects to Ln(II) centers through eta(2),micro(4)- and eta(2),micro(3)-carbonyls to generate a 2-D puckered sheet. In contrast, (THF)(5)EuCo(4)(CO)(11)]]( infinity ) (4) incorporates a C(2)(v)() symmetric cluster (two unique Co environments; two face-bridging, one edge-bridging, eight terminal carbonyls), and isocarbonyl linkages (eta(2),micro(4)-carbonyls) to Eu(II) atoms create a 1-D zigzag chain. Complexes 1-4 contain the first reported eta(2),micro(4)-CO bridges between a Ln and a transition-metal carbonyl cluster. Infrared spectroscopic studies revealed that the isocarbonyl associations to Ln(II) persist in solution. The solution structure and dynamic behavior of the Co(4)(CO)(11)](2)(-) cluster in 1 was investigated by variable-temperature (59)Co and (13)C NMR spectroscopies.