Abstract
The nuclear inelastic scattering signatures of the low-spin centers of the methanosulphonate, tosylate, and perchlorate salts of the spin crossover polymer ([Fe(II)(4-amino-1,2,4-triazole)3]2+)n have been compared for the low-spin phase, for the mixed high-spin and low-spin phases, as well as for Zn(II) diluted samples. Within this series a change in the vibrational pattern in the 320–500 cm−1 region is observed. Significant shifts and decreasing intensity of bands at ~320 cm−1 and bands over 400 cm−1 are observed as the molar fraction of the low-spin (LS) centers decrease. Density functional theory calculations using Gaussian09 (B3LYP/CEP-31G) for pentameric, heptameric, and nonameric model molecules yielded the normal modes of several spin isomers: these include the all high-spin (HS) and the all low-spin (LS) configuration but also mixtures of LS and HS centers, with a special focus on those with LS centers in a HS matrix and vice versa. The calculations reproduce the observed spectral changes and show that they are caused by strain extorted on a LS Fe(II) center by its HS neighbors due to the rigid character of the bridging aminotriazole ligand. Additionally, the normal mode analysis of several spin isomers points towards a coupling of the vibrations of the iron centers of the same spin: the metal-ligand stretching modes of the all LS and the all HS spin isomers reveal a collective character: all centers of the same spin are involved in characteristic normal modes. For the isomers containing both LS and HS centers, the vibrational behavior corresponds to two different subsets (sublattices) the vibrational modes of which are not coupled. Finally, the calculation of nuclear inelastic scattering data of spin isomers containing a ca. 1:1 mixture of HS and LS Fe(II) points towards the formation of blocks of the same spin during the spin transition, rather than to alternate structures with a HS-LS-HS-LS-HS motif.
Highlights
The azole bridged Fe(II) 1D polymer complexes, such as the 1,2,4-triazoles [1,2] or alkylene-linked bitetrazoles, are of special importance for the investigation of the spin crossover (SCO) [3,4,5,6] effect
We have presented a nuclear inelastic scattering and DFT study of the 1-D polymeric spin crossover 4-amino-1,2,4-triazole Fe(II) complexes which shows coupling of the vibrations involving the center of a given spin with the spin state of its neighbors
For the LS centers if the spin state of the neighbors is changed to HS the stretching of the remaining LS Fe(II) to lower frequencies and decoupling of the movement of its neighbors occur within the so modified mode
Summary
The azole bridged Fe(II) 1D polymer complexes, such as the 1,2,4-triazoles [1,2] or alkylene-linked bitetrazoles, are of special importance for the investigation of the spin crossover (SCO) [3,4,5,6] effect. Designed over twenty years ago [7,8,9] with the idea of enhancing the cooperative character of the spin transition by linking the iron centers with a system of covalent bonds, these systems have revealed fascinating chemistry. They exhibit a very strong dependence of the spin transition temperature. Magnetochemistry 2016, 2, 19 revealed fascinating chemistry They exhibit a very strong dependence of the spin transition temperature and the character of the transition on the type of the counter anions [2,10], the presence anodf hthyedcrhataerdacwteartoefr t[h1e1]t,raannsditioonn tohnethliegatynpdesoufbtshtietuceonutnt[e1r2,a1n3i]o. Tinhveeirrsoinoninctehneteinr viserdseionnotceedntaesr iFsed(1e)n, othteednaesxt Fec(e1n),trtohseynmemxtecternictarollsyyrmelmateetdriocanlelys arereladteednootneedsaasreFed(e2n)/oFtee(d2’a)s, FFee((32))//FFee(3(2’)’,),etFce.(3)/Fe(3’), etc
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
