Symmetry Reduction upon Size Mismatch: The Non‐Icosahedral Intermetalloid Cluster [Co@Ge₁₂]³⁻

Abstract

A new complex comprising [Co@Ge12]3– cluster core was synthesized through the reaction of CoMe(PMe3)4 and K4Ge9 in ethylenediamine solution. The pseudo‐D5d geometry of this cluster can be viewed as structurally derived from an icosahedral cage via Jahn‐Teller effect, leading to notable bonding differences from Ih‐[M@E12]q− clusters (E = Sn, Pb with q = 2, 3). The [Co@Ge12]3– cluster represents a structural conundrum. On the basis of the geometric considerations it could be viewed as a sandwich complex. However, chemical bonding analysis revealed that there is a direct covalent multicenter bonding between the two pentagons, thus indicating that the structure should be viewed as an elongated icosahedron. Further theoretical calculations on [M@Ge12]3− (M = Rh, Ir, Mt) indicate that similar compounds of larger‐size metal atoms can drive the complete transformation of [M@Ge12]3− clusters from icosahedron structure to a sandwich one.

Endohedral Plumbaspherenes of the Group 9 Metals: Synthesis, Structure and Properties of the [M@Pb12]3− (M=Co, Rh, Ir) Ions

“…They include [M@E 10 ] 2À (whereM = Ni, Pd, Pt;E = Pb), [9] the fluxional [M 2 @Sn 17 ] 4À ions (M = Ni, Pt) [1,10] and the [M@E 12 ] nÀ ions (where M = Ni, Pd, Pt, Au, Mn;E= Pb, n = 2, 3) to name af ew. [11][12][13][14][15][16][17][18][19] The icosahedral [M@E 12 ] nÀ clusters are ag rowing class of ions that have unique properties, such as high electronic degeneracies, rigorous I h point symmetry,a nd s-aromaticity that impartsu nusuals tability and anomalous NMR chemical shifts. The [M@Pb 12 ] 2À/3À plumbaspherenes (M = Ni, Pd, Pt, Rh, Mn, Au) [11][12][13][14][15] and [Ir@Sn 12 ] 2À have been crystallographically characterizeda nd are reminiscento ft he icosahedrals ubunits found in the solid state (e.g.…”

Electronic structure and bonding in endohedral Zintl clusters

“…Although this spectrum of bonding situations is most well characterised within the 12-vertex family, the same pattern of increasing participation of metal d electron density can also be identified in the 10-vertex analogues [Ni@Pb 10 ] 2À , marginally distorted but still deltahedral [Fe@Sn 10 ] 3À and the 3-connected [Co@Ge 10 ] 3À cluster discussed above. 158 compared to other [M@E 12 ] qÀ clusters that do exhibit distorted, yet still near-icosahedral structures: Au/Pb/3 (4n + 4 electrons, D 3d symmetry, top right), 176 Co/Ge/ 3 (4n + 2 electrons, approximate D 5d symmetry, bottom right), 177 Rh/Sb/3 (4n + 2 electrons, D 3d -symmetry, bottom centre), 169 Mn/Pb/3 (4n À 2 electrons, D 2h symmetry, bottom left). 178 There remains one further arrangement of 12 atoms in an electron deficient polyhedron around a single endohedral atom, the ternary cluster anion [Co@Sn 6 Sb 6 ] 3À (Fig.…”

“…175 A number of recent examples from the 12-vertex family with which we are primarily concerned in this review highlight the tendency to retain centrosymmetric geometries despite having electron counts that would be consistent with nido geometries. 169,[176][177][178] The [Au@Pb 12 ] 3À cluster is a particularly interesting example: 176 if we assume that the Au 5d electrons do not contribute to the total electron count, the skeletal electron count of 52 = 4n + 4 suggests that a nido geometry should be adopted, just as it is for [Ag@Pb 11 ] 3À . Instead, the X-ray structure reveals a highly distorted icosahedron, compressed along one C 3 axis to give D 3d -symmetry (Fig.…”

“…12, bottom left). 177 Despite having exactly the same 50-electron (closo) count as perfectly icosahedral [M@Pb 12 ] 2À (M = Ni, Pd, Pt), the icosahedron in [Co@Ge 12 ] 3À is significantly elongated along one 5-fold axis. Sun, Boldyrev and co-workers argued that size drives this distortion: the (formally negatively charged) Co atom is simply too large to fit inside the cavity of a Ge 12 2À icosahedron.…”

“…Fig.12Structure of the undistorted endohedral Zintl cluster [Pt@Pb 12 ] 2À with 50 = 4n + 2 valence electrons (top left)158 compared to other [M@E 12 ] qÀ clusters that do exhibit distorted, yet still near-icosahedral structures: Au/Pb/3 (4n + 4 electrons, D 3d symmetry, top right),176 Co/Ge/ 3 (4n + 2 electrons, approximate D 5d symmetry, bottom right),177 Rh/Sb/3 (4n + 2 electrons, D 3d -symmetry, bottom centre),169 Mn/Pb/3 (4n À 2 electrons, D 2h symmetry, bottom left) 178. …”