Reversible redox reactions in metal-supported porphyrin: the role of spin and oxidation state

Abstract

The reduced Co(i) metal ion in the molecular array facilitates the formation of the cobalt–ligand chemical bond already at RT. We demonstrate that molecular reactivity goes beyond the sole presence of unpaired electrons in the valence shell.

Distortion-driven spin switching in electron-doped metal porphyrins

“…Indeed, the adsorption on the highly reactive copper surface implies the filling of the adsorbate lowermost unoccupied MOs (up to the LUMO+3) and the concomitant TM(II) -TM(I) reduction. 18,19,23,24 Charge injection into the metal complex may also be induced by exploiting alternative pathways such as AM doping. Aimed to look into the TM reduction process, a NiTPP layer deposited on the Au(111) surface has been stepwise K doped.…”

“…17,33,41,42 The K binding to CoTPP red-shifts the spectrum main feature by 0.85 eV, a behavior tightly linked to the Co(II) -Co(I) reduction. 19 Moreover, the inspection of Fig. 5(b), where the N K-edge spectra of the pristine CoTPP/ Au(111) and after 15 minutes K dosing in s-and p-polarization are reported, clearly shows that the macrocycle distortion takes place right after the K doping.…”

“…Such a remarkable charge transfer (up to the LUMO+3) has already been revealed for the aforementioned NiTPP/Cu(100) and CoTPP/Cu(100) interfaces. 18,19,23 As a final remark, the peculiar work function (WF) trend as a function of the K dose (see Fig. 1(a)) deserves to be highlighted: (i) a significant WF drop, indicative of the formation of a new surface dipole induced by the adsorption of the K atoms at the interface, is present at the lower K doping level; such WF change is accompanied by a HOMO blue shift with respect to the Fermi level; (ii) a plateau region leading to the complete filling of the gas-phase unoccupied MOs up to LUMO+3 characterizes the intermediate K coverage; this range corresponds to the region of interest for the electron doping of the molecular layer; (iii) a further, less pronounced, WF drop determining a blue-shift of low-lying empty MO (LUMO/+1 and LUMO+3) takes place at higher K doses, which corresponds to the appearance of neutral K species in the K 2p XPS spectrum (see Fig.…”

“…In this respect, it has been shown that axial coordination may be exploited to modulate the TM oxidation and spin states. [17][18][19] In fact, the spin state of the Mn ion in the tetra-pyrrolic pocket may sweep across different configurations by subtle modification of the N ligand field, e.g., by changes of the Mn-ligand distance (HS in Mn-porphyrins, 20 IS in Mn-Pc 15 ) or of the ligand peripheral coordination (HS in Mn-TCNQ 4 metal-organic covalent networks). 21 Interestingly, it has been recently demonstrated that ruthenium tetraphenylporphyrin (RuTPP) on Ag(111) can be stabilized in two different conformations, saddle-shaped and planar, and only the former may axially interact with CO as a consequence of its greater molecular flexibility.…”

“…In this respect, it has been shown that axial coordination may be exploited to modulate the TM oxidation and spin states. 17–19 In fact, the spin state of the Mn ion in the tetra-pyrrolic pocket may sweep across different configurations by subtle modification of the N ligand field, e.g. , by changes of the Mn–ligand distance (HS in Mn–porphyrins, 20 IS in Mn–Pc 15 ) or of the ligand peripheral coordination (HS in Mn-TCNQ 4 metal–organic covalent networks).…”