The [M2(CO)8] Complexes of the Cobalt Group

Abstract

A theoretical study of the carbonyl complexes [M 2 (CO) 8 ] of the group 9 metals (M = Co, Rh, Ir) is presented. Three isomers were found for each metal, with the relative stabilities and energies differing from one metal to another, and two transition states corresponding to their interconversion processes were identified. The minima in the potential energy surface have been fully characterized through a vibrational

Spontaneous dissociation of Co2(CO)8and autocatalytic growth of Co on SiO2: A combined experimental and theoretical investigation

“…The structural parameters obtained from our DFT studies, such as the distance between the two cobalt atoms (2.52 Å) and the distance to the bridging (1.95 Å) and terminal ligands (1.81 Å) from the metal atom, match the reported values well [58]. Further, we find the D 3 d symmetric structure to be less stable by 6.9 kcal/mol with respect to the C 2 v isomer compared to the reported value of 5.8 kcal/mol [27]. Electronic-structure analysis indicates that the highest occupied orbital (HOMO) is dominated by Co 3d orbitals (Fig.…”

“…Sumner et al reported a C s symmetric structure resembling the C 2 v symmetry (Fig. 5), which was analyzed by DFT calculations [27]. Less stable D 2 d and D 3 d isomers that do not have the bridging ligands have also been observed in solution [55–57].…”

[1,1‐Co2(CO)6(CNAr)2]: A Structural Mimic of the Elusive D2d Isomer of [Co2(CO)8]

“…Solution IR spectroscopy studies on disubstituted Co 2 (CO) 6 L 2 dimers featuring mono‐ and bidentate neutral‐donor ligands have similarly revealed an equilibrium between multiple isomers 9–13. In the solid state, however, only the well‐known C 2 v isomer featuring two symmetric bridging carbonyl ligands14 and the unbridged D 3 d form have been established crystallographically for the parent octacarbonyl complex15, 16 and numerous substituted derivatives 17. 18 The third, D 2 d ‐symmetric isomer, which is unbridged and possesses two mutually orthogonal trigonal bipyramidal Co centers, has thus far eluded structural characterization in all systems,16, 17, 19 despite being proposed as the lowest energy isomer of Co 2 (CO) 8 17, 20 and a significant fraction of the Co 2 (CO) 8 isomeric mixture in solution at room temperature 7…”

“…Relative to the structurally characterized isomers of Co 2 (CO) 8 , this CoCo separation falls at an intermediate value between the bridged‐ C 2 v (2.5301(8) Å)15b and unbridged‐ D 3 d (2.700(2) Å)16 forms. Notably, DFT calculations on the D 2 d isomer of Co 2 (CO) 8 have predicted a CoCo length that is likewise intermediate between those of the C 2 v and D 3 d isomers 17. 20, 22 The [Co(CO) 2 (CNAr) 2 ] unit of 1,1‐Co 2 (CO) 6 (CNAr) 2 possesses a near‐trigonal bipyramidal coordination geometry, with an equatorial plane containing the CoCo bond vector ( Σθ °(Co1)=360°) and axial CNAr ligands that are slightly bent toward the [Co(CO) 4 ] fragment (C1‐Co1‐C2=166.14(14)°).…”

Internal carbon monoxide exchange and CO dissociation in cobalt carbonyl carbene complexes. A density functional study

“…However in metal carbonyl clusters the so-called tripodal rotation of the M(CO) 3 moiety is a commonly observed exchange process as well [11]. It is known that the interconversion processes take place with rather small activation energies, namely 3 and 8.4 kcal/mol at B3LYP/ LANL2DZ level [12], which are smaller than the 11.7 ± 0.6 value measured by solid-state 13 C NMR spectroscopy [13].…”