Lanthanide−Transition-Metal Carbonyl Complexes. 1. Syntheses and Structures of Ytterbium(II) Solvent-Separated Ion Pairs and Isocarbonyl Polymeric Arrays of Tetracarbonylcobaltate

Transmetalation reactions of metallic ytterbium with Hg[Co(CO)4]2 in the coordinating solvents pyridine and THF
yield the solvent-separated ion pairs [Yb(L)6] [Co(CO)4]2 (1a, L = Pyr; 2a, L = THF). The IR spectrum of 1a in
pyridine indicates that the tetracarbonylcobaltate anion is not directly bonded to the divalent Yb cation owing to the
strong coordinating ability of pyridine. On the other hand, IR spectra of 2a in THF are concentration dependent. In
dilute solutions there is an equilibrium between the solvent-separated ion pair and a weak contact ion pair. Higher
concentrations of 2a facilitate the formation of a tight ion pair that has a low-frequency isocarbonyl absorption.
Remarkably, complexes 1a and 2a are easily transformed in toluene into the two-dimensional sheetlike arrays
[(Pyr)4Yb{(μ-CO)2Co(CO)2}2]∞ (1b) and [(THF)2Yb{(μ-CO)3Co(CO)}2·Tol]∞ (2b). The two-dimensional frameworks
are supported by isocarbonyl linkages. Infrared spectra of toluene solutions substantiate the existence of the
isocarbonyl bridges with low-frequency absorptions at 1780 cm-1. Compounds 1b and 2b belong to a rare class
of lanthanide−transition-metal carbonyl extended arrays, only three others of which have been structurally established.
Dissolving 1b in pyridine regenerates 1a, but the complete conversion of 2b into 2a cannot be achieved. Crystal
data:  1a·Pyr is monoclinic, P21/c, a = 11.171(1) Å, b = 11.925(1) Å, c = 33.978(1) Å, β = 95.10(1)°, Z = 4;
2a is monoclinic, C2/c, a = 17.724(1) Å, b = 12.468(1) Å, c = 18.413(1) Å, β = 100.34(1)°, Z = 4; 1b is
monoclinic, C2/c, a = 11.047(1) Å, b = 13.423(1) Å, c = 21.933(1) Å, β = 103.49(1)°, Z = 4; 2b is monoclinic,
C2/c, a = 28.589(1) Å, b = 7.223(1) Å, c = 14.983(1) Å, β = 118.90(1)°, Z = 4.