Structural trends in ten-vertex endohedral clusters, M@E(10) and the synthesis of a new member of the family, [Fe@Sn10]3-

The synthesis of a new endohedral ten-vertex Zintl ion cluster, [Fe@Sn10](3-), isoelectronic with [Fe@Ge10](3-), is reported. In an attempt to place this new cluster within the context of the known structural chemistry of the M@E10 family (M = transition metal, E = main group element), we have carried out a detailed electronic structure analysis of the different structural types: viz bicapped square antiprismatic ([Ni@Pb10](2-), [Zn@In10](8-)), tetra-capped trigonal prismatic ([Ni@In10](10-)) and the remarkable pentagonal prismatic [Fe@Ge10](3-) and [Co@Ge10](3-). We establish that the structural trends can be interpreted in terms of a continuum of effective electron counts at the E10 cage, ranging from electron deficient (<4n + 2) in [Ni@In10](10-) to highly electron rich (>4n + 2) in [Fe@Ge10](3-). The effective electron count differs from the total valence electron count in that it factors in the increasingly active role of the metal d electrons towards the left of the transition series. The preference for a pentagonal prismatic geometry in [Fe@Ge10](3-) emerges as a natural consequence of backbonding to the cage from four orthogonal 3d orbitals of the low-valent metal ion. Our calculations suggest that the new [Fe@Sn10](3-) cluster should also exhibit structural consequences of backbonding from the metal to the cage, albeit to a less extreme degree than in its Ge analogue. The global minimum lies on a very flat surface connecting D4d, C2v and C3v-symmetric minima, suggesting a very plastic structure that may be easily deformed by the surrounding crystal environment. If so, then this provides a new and quite distinct structural type for the M@E10 family.

‘Classical’ and ‘Abnormal’ Bonding in Tin (II) N-Heterocyclic Carbene Complexes

Reaction of Sn(OTf)2 (OTf– = OSO2CF3–) with one and two equivalents of the N-heterocyclic carbene (NHC) 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) yielded the complexes [Sn(IPr)(OTf)2] (1) and [Sn(IPr)(aIPr)(OTf)][OTf] (2), respectively. Both species were characterised by single crystal X-ray diffraction, multi-element NMR spectroscopy, and elemental analysis. Both compounds display an NHC ligand bonded to the tin(ii) metal centre via the C2 carbon in a ‘classical’ mode, while 2 also contains an ‘abnormal’ C4/C5-bonded carbene (aIPr). These observations highlight the subtle steric and electronic effects affecting the coordination modes of these ligands. Solution phase NMR experiments on 1 and 2 reveal complex behaviour resulting in the protonation of the IPr ligands to yield the 1,3-bis(2,6-diisopropylphenyl)-imidazolium cation via an unidentified reaction mechanism.

[Co(η5-P5){η2-P2H(mes)}]2-: a phospha-organometallic complex obtained by the transition-metal-mediated activation of the heptaphosphide trianion

A carbon copy: The chemical activation of the heptaphosphide trianion with [Co(PEt(2)Ph)(2)(mes)(2)] (see picture; 1) yields the novel phospha-organometallic complex [Co(η(5)-P(5)){η(2)-P(2)H(mes)}](2-) (2). The reaction product maintains the nuclearity of the parent cluster, but extensive cage fragmentation takes place to yield a diamagnetic "inorganometallic" cobalt complex.

Synthesis and isolation of [Fe@Ge(10)](3-): a pentagonal prismatic Zintl ion cage encapsulating an interstitial iron atom

Reaction of an ethylenediamine (en) solution of the Zintl phase precursor K(4)Ge(9) with FeAr(2) (Ar = 2,6-Mes(2)C(6)H(3)) in the presence of 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) yielded the endohedral Zintl ion [Fe@Ge(10)](3-) (1) which was crystallographically characterized as a [K(2,2,2-crypt)](+) salt in [K(2,2,2-crypt)](3)[Fe@Ge(10)]*2en. This unprecedented Zintl ion exhibits a pentagonal prismatic 10-atom germanium cage with an interstitial iron atom in the central cavity. Confirmation of the existence of the cluster anion in solution was corroborated by positive and negative ion mode electrospray mass spectrometry.