CODECS 2013 Workshop
San Lorenzo de El Escorial, Madrid, 18th –22nd April, 2013
Spin-crossover in a Ni-porphyrin with a phenylazopyridine substituent
Gerard Alcovera, Coen de Graafa,b, Maria Àngels Carvajala, Rosa Caballola,
a
Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel·lí Domingo s/n,
43007, Tarragona, Spain
Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluis Companys 23,
08010 ,Barcelona, Spain
b
[email protected]
NiII is known to form complexes in two different spin states depending on the coordination
number (n = 4, 5 and 6). Square planar complexes (n = 4), Ni2+ tend to be low spin (S=0), while
octahedral complexes (n = 6) are usually high spin (S=1). Square pyramidal complexes (n = 5)
can be high or low spin depending primarily on the electronegativity of the ligands but also on
the geometrical details of the coordination sphere1.
Recently, light-induced spin-crossover has been reported in a Ni-porphyrin functionalized
with a phenylazopyridine ligand2. Upon light irradiation (500 nm), the azopyridine moiety
induces a change in the NiII coordination sphere from square planar (n = 4) to square pyramid (n
= 5), leading to a change in the total spin of the molecule from S = 0 to S = 1. The back reaction
is induced by visible light (435 nm). Figure 1 summarizes the spin and coordination changes
upon irradiation. The trans-cis isomerization in the azopyridine ligand has been proposed to
trigger the spin-crossover effect.
Fig. 1. Light induced spin-crossover on phenylazopyridine functionalized Ni-porphyrine.
To elucidate the light-induced spin-crossover mechanism for this NiII compound, DFT and
CASPT2 calculations have been performed. We explore the relative stabilities of 4- and 5-fold
coordinated species with cis and trans-azopyridine ligand and determine the excitation energies
of the different species.
Acknowledgments
Financial support has been provided by the Spanish Ministry of Economy and Competitvity
(Project CTQ2011-23140), the Generalitat de Catalunya (Project 2009SGR46 and Xarxa de
Referència d’R+D+I en Química Teòrica i Computacional, XRQTC) and Codecs Cost Action
MC1002.
References (please, use this style, times New Roman 10)
1. S. Thies, H. Sell, C. Schutt, C. BornHoldt, C. Nather, F. Tuczek, R. Herges. J. Am. Chem. Soc. 133,
16243 (2011)
2. S. Venkataramani, U. Jana, M. Dommaschk. Science, 331, 445 (2011).