Electronic structures of metal complexes containing the π-cyclopentadienyl and related ligands. Part 2.—He I photoelectron spectra of the open-shell metallocenes

Abstract

He I photoelectron spectra are reported for the metallocene species ( C5H&V, (C,H,),Cr, (C5H&Mn, ( C S H 5 ) 2 C ~ and (C5H5)2Ni, and for their 1,l'-dimethyl derivatives. The metal 3d ionisation structure is discussed in terms of ligand field theory. The unusual spectrum of (CSH4Me)2 Mn is interpreted in terms of a high-spin/low-spin equilibrium in the gas phase.

Supramolecular Catalysis of Orthoformate Hydrolysis in Basic Solution: An Enzyme-Like Mechanism

“…7 The gas phase electron diffraction data of (MeC 5 H 4 ) 2 Mn have been interpreted as consisting of two monomeric spin isomers, where the ratio of high-spin (Mn-C(ave)= 2.43 Å) to lowspin (Mn-C(ave)= 2.14 Å) is 60:40 at 100 °C. 8,9 This gas phase structural study supports the deductions of earlier gas phase photoelectron spectroscopy (PES) studies that (MeC 5 H 4 ) 2 Mn is a spin equilibrium molecule in gas phase while Cp 2 Mn exists predominantly as the high-spin isomer. 10 The EPR studies of Ammeter and Maki have shown that Cp 2 Mn and (MeC 5 H 4 ) 2 Mn in frozen solution and doped in a host matrix of Cp 2 M or (MeC 5 H 4 ) 2 M (M= Mg, Fe), respectively, behave as spin crossover molecules, where a low-spin (LS) state is stabilized by about 0.5 kcal mol -1 .…”

Cobaltocene adsorption and dissociation on Cu(111)

“…1) at 9.0 ± 0.2 eV (peak B), 12.7 ± 0.2 eV (peak C), and 17.3 ± 0.2 eV (peak D) as well as the much weaker features at 0.9 ± 0.2 eV (peak A′) and 5.1 ± 0.2 eV (peak A″) are similar in relative intensities and binding energies to those assigned to cobaltocene adsorbed on cleaved graphite [32]. There is also a strong similarity between the gas phase photoemission spectra of cobaltocene [36][37], but with a shift of about 4 eV in the energy scale, as is typical of metallocenes [13][14][15], [17], [20][21][22][23], and [32], even though the moleculesubstrate as well as intermolecular interactions may shift, or broaden the molecular orbitals.…”

“…The big difference among these three metallocenes appears to be that the "nineteen electron" cobaltocene has a single unpaired electron resulting in a low ionization potential [32] of 5.56 eV [37] when compared to ferrocene (6.88 eV [37]) and nickelocene (6.51 eV [37]). This results in formation of a surface species that somewhat resembles [Co(Cp) 2 ] + on graphite [32] but apparently leads to fragmentation on Cu (1 1 1).…”

“…Based on theoretical calculations of the ground-state molecular orbitals of cobaltocene [38], fi nal excited states [38] and gas-phase photoemission studies [36][37], we can assign these photoemission features of the adsorbed species and the induced photoemission features to the molecular orbitals of cobaltocene. With very large cobaltocene exposures (Fig.…”

Direct observation of low spin – high spin electronic ground states and cross-over exchange in manganocene derivatives, (η5-C5H4R)2Mn, R = H, CH3, C2H5 by paramagnetic nuclear magnetic resonance

“…(1) and its 1,l '-dimethyl substituted derivative (-q5-C5H4CH3),Mn (2) (3)(4)(5). Moreover, the electronic state associated with the other possible 1s configuration, e;,ai,, or 'A,, state, is generally considered too far above the ground state energy level to be significantly populated or involved in a multiple ground state cross-over exchange process (6).…”