Prediction of spin transition properties in 1,2,4 H-triazole iron(II) complexes using computational method

• Main Author: Wahyu Nugraha, Asep
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/32172
• Institution: Institut Teknologi Bandung

The octahedral complex compounds with the iron(II) having a d6 electronic configuration can be in two different electronic states i.e low spin or high spin. When the iron(II) bind to strong ligands, all the electrons in the d orbital are in pairs so that the complex is diamagnetic, otherwise the iron(II) bind to weak ligands then four electrons in the d orbital are unpaired therefore that the complex is paramagnetic. In the intermediate ligand field, the energy difference between the two states are relatively small and several external influences can lead to changes in their spin states. This phenomenon is called spin transition (ST) which can be occurs reversibly. Most of the ST events were observed by temperature changes to the changes magnetic susceptibility. The plot of magnetic susceptibility of the compounds versus temperature obtained is called ST pattern. From the curve, the transition temperature (T½) can be determined as the temperature at which high-spin fraction equal to the fraction of low spin. Complex compounds with transition changes in a narrow range temperature can be used as switch material, and if the transition pattern upon heating is different from a cooling mode causing potential as a data storage material. Ligan of 1,2,4 H-triazole (Htrz) is the ligand with an intermediate strength. The ligand has three N donor atoms but only two N atoms which can donate a pair of electron to the central metal ion to form a complex compound. The position of two N atoms are very close, therefore that the bond coordination occurs to the different metal ions and the complexes formed a polymeric structure. The complex of iron(II) with the ligand Htrz has the ST characteristics in a contrast color change. Several studies shown that this complex is in a powder form with the iron(II) binding to the six Nitrogen atoms of the three ligands resulting the formula of [Fe(Htrz)3]2+. Further studies found that one of ligand Htrz is deprotonated become trz-1 and the molecular formula obtained is [Fe(Htrz)2(trz)]+1. So far the single crystals of the complex have not been obtained and the exact chemical formulas cannot be determined accurately. The computational methods have been used to study various ST characteristics on several complex compounds. The computational methods can be a solution to ensure molecular formula of iron(II) with the Htrz ligand accordingly. Because of the complex iron(II) with the ligand Htrz has a polymeric structure, it requires modeling complex structures appropriate to describe the complex polymeric A model (notated A1) consists of two Fe(II) ions and six the Htrz ligand, while the B model with the shortest chain by notation B1 consists of two Fe(II) ions and the nine of Htrz ligands. The model fragment extension for both models is done by adding two Fe(II) ions and the six ligand Htrz with the notation 2 and 3. Six of the structure models have been used in computational calculations to determine the appropriate molecular formula, the temperature ST and ST pattern. To achieve these objectives, the stages of the study include is determine the model of the polymeric structure, preparation input data based on the model, perform calculations on the low spin state and high spin state, visualization of structure of the geometry optimization results, and determination of the temperature ST and the ST pattern based on thermodynamic data. The novelty is to get six models fragmentation polymeric complex, the molecular formula of the complex, ST temperature, and the ST pattern. The fundamental contributions to the field of science are to predicting the ST of temperature and ST pattern of the polimeric complex. he computational chemistry in this study used software of Gaussian 09 Revision D.01 with UHF, B3LYP, M06-2x, and TPSSh hybrid functions with 3-21G, 6-31G (d), 6-31G (d, p) , and TZVP basis set. The order of hybrid functions and the basis set above shows the order of the accuracy level. The hybrid function of M06-2x, and TPSSh are the best accuracy. Determination of the ST characteristic using hybrid function/ basis set of TPSSh/ TZVP. The computational chemistry data in this study were compared with experimental data. Results of this study indicate that model fragment A1 can be used determine the molecular formula of polymeric complex, whereas the model fragment B2 can be used to determine of the structure of the complex in the low spin state and the high spin state, the ST temperature (T½), and the ST patterns. Based on the results obtained by the computational method that the complex molecular formula of iron(II) Htrz complex is ([Fe(Htrz)2(trz)]+)n. The distance between the Fe(II) on the low spin state is 3.67? - 3.71? and the high-spin state is 3.98? - 4.07?, while the bond length of Fe-N in the low spin state is 1.97? - 2.02? and high spin is 2.07 ? - 2.33?. Based on dihedral angle data of the Fex-Np-Nq-Fey of geometry optimization results showed that the high-spin state of angle between field of Fex-Np and field of Nq-Fey is greater than on the low spin state. The ST temperature complexes of iron(II) Htrz with a model fragment B2 is 342K and a model fragment B3 is 348K. The ST patterns of iron(II) Htrz complex calculation results has the ST pattern slowly and does not depict hysteresis.