Anjana Rai-Chaudhuri

Synthesis and magnetic properties of 1:1 salts containing the bis(η6-hexamethylbenzene)cobalt cation

The salts [Co(η6-C6Me6)2]+[A]–(A = BPh4, NbF6, PF6 or SbF6) have been prepared from anhydrous CoCl2. Solid-state magnetic susceptibility measurements on these salts indicate that they all obey the Curie–Weiss law in the temperature range 30–300 K with µeff= 2.7, 2.8, 2.8 and 2.6 µB with corresponding θ values of –1.4, 0.2, –4.1 and 0.4 K for the BPh4–, NbF6–, PF6– and SbF6– salts respectively. Below 20 K, the magnetic susceptibility for all the salts deviate substantially from the Curie–Weiss law. The experimental susceptibility data for the compounds [Co(η6-C6Me6)2]+[BPh4]– and [Co(η6-C6Me6)2]+[NbF6]– can be fitted to a model in which the 3A2g triplet ground state assigned to the [Co(η6-C6Me6)2]+ moiety exhibits a positive zero-field splitting of 17.8 and 20.5 cm–1 respectively. In contrast, the magnetic susceptibilities for [Co(η6-C6Me6)2]+[A]–(A = PF6 or SbF6) cannot be fitted to this model in the range 2–30 K due to more significant intermolecular antiferromagnetic spin–spin interactions. All the salts were EPR silent at between 4 and 300 K both in the solid state and in frozen solution. Reaction of [Co(η6-C6Me6)2]+[PF6]– with either [NBu4][tcnq](tcnq = tetracyano-p-quinodimethane) or [NBu4][C3{C(CN)2}3][C3{C(CN)2}3= tris(dicyano-methylene)cyclopropane] gave insoluble paramagnetic precipitates with µeff= 4.1 and 4.5 µB and θ values of –12.9 and –3.5 K respectively.

Electronic structure factors of Ge–H bond activation by transition metals. Photoelectron spectra of [Mn(η5-C5H5)(CO)2(HGePh3)], [Mn(η5-C5H4Me)(CO)2(HGePh3)], and [Mn(η5-C5Me5)(CO)2(HGePh3)]

The He I photoelectron spectra of [Mn(η5-C5H5)(CO)2(HGePh3)], [Mn(η5-C5H4Me)(CO)2-(HGePh3)], and [Mn(η5-C5Me5)(CO)2(HGePh3)] have been obtained to measure the nature and extent of Ge–H bond interaction with the transition metal centre in these complexes. The principal electronic structure factors contributing to the addition of the Ge–H bond to the transition metal involve the interaction of the Ge–H σ and σ* orbitals with the metal. The shape and splitting pattern of the metal-based ionisation band indicates the extent of Ge–H σ* interaction. The electron distribution between the Ge–H bond and the metal is indicated by the relative stabilities of the metal- and ligand-based ionisations. The electron charge-density shift from the metal to the ligand is negligible in these three complexes and the metal ionisations reflect the formal d6 electron count at the metal centre. The electronic structure of the Ge–H interaction with the metal is in the initial stages of Ge–H bond addition to the metal, before oxidative addition has become prevalent. The mechanism of interaction of the Ge–H bond with the manganese centre is predominantly through interaction of the filled Ge–H σ-bonding orbital with the empty metal orbitals. It is concluded that the magnitude of Ge–H σ interaction with the metal centre is similar to that of the corresponding Si–H σ interaction.

Experimental Comparison of the Bonding in Inorganometallic and Organometallic Complexes by Photoelectron Spectroscopy

The broad strides that have been made in recent years in the synthesis and structural characterization of organometallic and inorganometallic complexes have led to increasing interest in understanding the electronic structure and bonding in these molecules. The principles and models of bonding that have developed for organometallic complexes, as typified by the Dewar—Chatt— Duncanson model of synergistic metal—ligand bonding, have also provided the foundation for understanding the chemical and physical properties of inorganometallic complexes. These principles go beyond the basic crystal field or valence bond descriptions of d-orbital splitting diagrams of classical coordination compounds. The models now consider the precise electron-donor, electron-acceptor, and bond-forming capabilities of the ligands. For every interaction of an organic ligand with a metal there is a symmetry-equivalent interaction of an inorganic ligand with a metal. This has been termed the “isolobal analogy.”(1,2) The differences lie in the precise spatial distribution and energy of the valence electrons of the ligands. Experimental approaches are essential to obtain a quantitative comparison of the electron distribution and bonding of organic and inorganic ligands with transition metals.