Spin Crossover in Nickel(II) Tetraphenylporphyrinate via Forced Axial Coordination at the Air/Water Interface.

Alexander G Martynov,Yulia G Gorbunova,Alexander A Dmitrienko,Andrey P Kroitor,Alexander V Shokurov,Aslan Yu Tsivadze,Sofiya L Selektor,Yulia Yu Enakieva,Daria S Kutsybala

doi:10.3390/molecules26144155

Abstract

Coordination-induced spin crossover (CISCO) in nickel(II) porphyrinates is an intriguing phenomenon that is interesting from both fundamental and practical standpoints. However, in most cases, realization of this effect requires extensive synthetic protocols or extreme concentrations of extra-ligands. Herein we show that CISCO effect can be prompted for the commonly available nickel(II) tetraphenylporphyrinate, NiTPP, upon deposition of this complex at the air/water interface together with a ruthenium(II) phthalocyaninate, CRPcRu(pyz)2, bearing two axial pyrazine ligands. The latter was used as a molecular guiderail to align Ni···Ru···Ni metal centers for pyrazine coordination upon lateral compression of the system, which helps bring the two macrocycles closer together and forces the formation of Ni–pyz bonds. The fact of Ni(II) porphyrinate switching from low- to high-spin state upon acquiring additional ligands can be conveniently observed in situ via reflection-absorption UV-vis spectroscopy. The reversible nature of this interaction allows for dissociation of Ni–pyz bonds, and thus, change of nickel cation spin state, upon expansion of the monolayer.

Highlights

Axial coordination of molecules and anions to metal centers in tetrapyrrole compounds represents one of the generally acknowledged approaches to control photophysical and redox properties of these compounds, occurring in a large number of natural processes and technical applications [1]
We show that coordination-induced spin crossover (CISCO) effect can be prompted for the commonly available nickel(II) tetraphenylporphyrinate, NiTPP, upon deposition of this complex at the air/water interface together with a ruthenium(II) phthalocyaninate, CRPcRu(pyz)2, bearing two axial pyrazine ligands
In the present work we study the possibility to achieve CN5 and CN6 states for a readily available nickel(II) tetraphenylporphyrinate, NiTPP, via forced axial coordination by pyrazine ligands incorporated into rruuthenium(II) tetra-15-crown-5-phthalocyaninate, CCRRPPccRRuu((ppyyzz))22 ((FFiigguurree 33))

Summary

Introduction

Axial coordination of molecules and anions to metal centers in tetrapyrrole compounds represents one of the generally acknowledged approaches to control photophysical and redox properties of these compounds, occurring in a large number of natural processes and technical applications [1]. We show that CISCO effect can be prompted for the commonly available nickel(II) tetraphenylporphyrinate, NiTPP, upon deposition of this complex at the air/water interface together with a ruthenium(II) phthalocyaninate, CRPcRu(pyz)2, bearing two axial pyrazine ligands.

Results

Conclusion