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Vanadium phthalocyanine (VPc) monolayers and multilayers were synthesized on Ag(111), and the electronic and magnetic states of an unachieved VPc with a divalent state of V were investigated. The VPc monolayer was fabricated by directly depositing the V atoms on a metal-free phthalocyanine (H2Pc) monolayer under ultra-high-vacuum conditions. The VPc multilayer was synthesized by repeated VPc monolayer deposition and subsequent sample annealing at approximately 450 K. The N 1s X-ray photoelectron spectra (XPS) of these samples showed a remarkable reduction in the peak assigned to H-bonded N atoms, concomitant with the appearance of a new peak attributed to V-bonded N atoms close to the peak of iminic N. Additionally, the oxidation state of V estimated from the V 2p XPS peak position corresponded to 1.6 and 2.4 in the monolayer and multilayer samples, respectively. These results clearly imply that VPc monolayers and multilayers were successfully obtained. The main ground-state electronic configuration of the V center was found to be 2Eg by angle-dependent V L-edge X-ray absorption spectroscopy. Furthermore, X-ray magnetic circular dichroism (XMCD) measurements suggest that this 2Eg state was mixed with the 2A1g state by spin–orbit coupling in the ground state. Data revealed that VPc shows a paramagnetic state on the Ag surface and in an H2Pc film but an antiferromagnetic state in the multilayer. Partial electron charge transfer was also observed from the Ag surface to the V center at the VPc/Ag(111) interface, leading to a significant decrease in XMCD signals in the monolayer.
Eguchi et al. (2015) studied this question.