Photoinduced HS state in the first spin-crossover chain containing a cyanocarbanion as bridging ligand

TLDR: The compound [Fe(abpt)(2)(tcpd)], which has been characterised as the first SCO molecular chain involving a cyanocarbanion as bridging ligand, is described.

About: This article is published in Chemical Communications.The article was published on 2009-06-05 and is currently open access. It has received 60 citations till now. The article focuses on the topics: Bridging ligand & Spin crossover.

Figures

Fig. 2 Thermal variation of the wmT product (K), light irradiation at 10 K (l = 514 nm) and thermal variation of the wmT product for 1 after irradiation (J). Inset: derivative of the thermal variation of the wmT product on increasing temperature after irradiation showing the T(LIESST) value.

Fig. 1 (a) ORTEP structure of the disordered bridging tcpd2 anion; (b) ORTEP perspective view of a possible portion of the 1-D structure of 1 at 293 K. Code of equivalent positions: (a) 1 x, 2 y, z; (b) 2 x, 2 y, z; (c) 1 + x, y, z; (d) 1 + x, y, z; (e) x, 2 y, z.

Frequently asked questions

Q1. What have the authors contributed in "Photoinduced hs state in the first spin-crossover chain containing a cyanocarbanion as bridging ligandw" ?

Iron ( II ) metal complexes involving the octahedral coordination sphere [ FeN6 ] are the most studied SCO compounds. To better explore the cooperative effect between the active metal sites, Kahn et al., and others, introduced an interesting and alternative approach based on the use of neutral suitable bridging ligands to covalently connect the metal centres. In this context, their strategy is to extend this polymeric approach to anionic ligands involving several potentially donating nitrogen atoms ( Scheme 1 ). In their ongoing work on the new potentially bridging cyanocarbanion ligands, the authors have shown in the last few years that their structural and electronic characteristics ( original coordination modes and high electronic delocalization ) can be tuned by slight chemical or electrochemical modifications such as substitution of functional groups or variation of the negative charge. Recently the authors have reported the first SCO series based on the tcm ( [ C ( CN ) 3 ] ), tcnome and tcnoet ligands and abpt co-ligand ( Scheme 1 ). A further step in this direction would be the preparation of original extended SCO networks bearing the Fe-abpt complexes by using covalent bonds. Here the authors show how the use of potentially bridging dianionic ligands bearing different coordination sites constitute a very good and simple method to perform this task. The authors report herein the first SCO iron ( II ) molecular neutral chain [ Fe ( abpt ) 2 ( tcpd ) ] ( 1 ) involving an anion as bridging ligand. To the best of their knowledge, only two SCO molecular chains involving bridging anions have been reported. 

Q2. What is the bridging mechanism for the polynitrileunit?

In this series, the single charge on theanion induces a terminal coordination mode for the polynitrileunit, resulting in neutral discrete SCO complexes. 

Q3. What is the important question in the field of magnetic molecular materials?

The design of new molecular compounds exhibiting the spincrossover phenomenon (SCO) is one of the most relevant andchallenging questions in the field of magnetic molecular materials. 

Q4. What is the role of the intermolecular interactions in a SCO?

In such materials, the intermolecular interactions(p-stacking, hydrogen bonding and van der Waals interactions) play a crucial role to transmit the transition. 

Q5. What is the structure of the cyanocarbanion ligand?

The cyanocarbanion ligand adopts am2-bridging mode via two nitrogen atoms of two different C(CN)2 wings leading to a chain structure as depicted in Fig. 

Q6. What is the atypical feature of the wmT product?

Such atypical feature may be explained by the contraction, just below 170 K, of the FeII coordination sphere due to theHS–LS transition leading to an increase of the energy gap between HS and LS levels of one or two neighbouring FeIIions along the chain. 

Q7. What is the effect of the HS state in the sample?

Asthe colour of the sample is basically not so deep, a problem ofpenetration depth can be ruled out, this effect can rather beattributed to a competition between excitation and an efficientHS–LS relaxation process, also illustrated by the relativelysmall T(LIESST) temperature of 35 K. 

Q8. What is the effect of the zero-field splitting of the individual HS state?

The smalldecrease of the magnetic signal recorded below 25 K can beattributed either to the zero-field splitting of the individualphoto-induced HS state and/or to a small antiferromagnetic coupling between the FeII HS states in the 1-D chain, as reported with a larger magnitude for FeII dinuclear complexesand for some chain complexes with the same bridging tcpd2 ligand. 

Q9. What is the average Fe–Ndistances at room temperature?

The average Fe–Ndistances at room temperature and at 10 K ‘‘flash cooled’’ arein the range expected for 100% and 50% of the HS iron(II), respectively. 

Q10. What is the important question in the field of magnetic materials?

In this context, the authors have directed their effortsto the preparation of new SCO polymeric systems based onsuch bridging anions, for which the magnetic properties areessentially governed by subtle structural changes and thereforeby the nature of the cyanocarbanion ligand.