Study On The Magnetic Complexes With Multi-magnetic Centers

The magnetic coupling interaction between metal centers of complexes has attracted much attention.For a long time,Hamiltonian operators have been widely used to describe the phenomenon of magnetic coupling interaction between metal centres.By expanding the expression of Hamilton operator,many simulation formulas are obtained.Finally,the strength of the interaction is evaluated by the numerical value of the magnetic coupling parameters.However,at present,many simulation formulas have difficulties in identifying the structure of the model correctly and analyzing the complex objects.Most of the results can only be evaluated by calculating accuracy,which greatly hinders the development of magnetic simulation calculation.In order to better integrate and evaluate the correctness and applicability of the existing simulation formulas.This paper innovatively introduces the statistical method of MCMC(Markov chain Monte Carlo)to fit the formula of simulation calculation with experimental data.The fitting formula is evaluated comprehensively by calculating the probability distribution of parameters and the correlation distribution among parameters.In order to reduce the influence factors of magnetic coupling parameters and based on the benchmark that the electron orbits of central metal ions play a decisive role in the magnetic coupling interaction,the binuclear copper(II)and chain cobalt(II)structural units were selected as model complexes for magnetic research.Five most commonly used simulation formulas are selected.The results are as follows:(1)Based on hydroxyl-bridged binuclear copper(II)complexes,four types of model complexes were screened.These configurations are classified by overlapping p-orbital electron clouds of hydroxyl oxygen atoms with different d-orbitals of copper ions.The results show different magnetic properties.MCMC method is introduced to calculate and simulate the data performance of all structures under four different fitting formulas.It is found that MCMC method can get the best values from the four models.However,unlike previous studies,this paper innovatively distinguishes and determines the best fitting formula from the MCMC calculation results,and points out the existing problems of the fitting formula through the evaluation of the correlation distribution.(2)In order to increase the range of model complexes,eight model complexes with different structure types were screened based on azide-bridged binuclear copper(?)complexes.Unlike hydroxyl bridging groups,azide ions have two common bridging modes(?1,1 and ?1,3),so their magnetic properties have changed more profusely.Subsequently,the MCMC method is also introduced in the paper to evaluate the applicability and correctness of the fitting formula.(3)In order to test whether four fitting formulas can be evaluated by MCMC method in different types of Binuclear cells.The magnetic properties of three thiocyanate-bridged complexes were synthesized and tested by introducing a similar binuclear structure unit system.Finally,MCMC method is still used to simulate the four fitting formulas.Based on the experimental data,the calculated results of the fitting formula in binuclear copper(II)complexes were evaluated.It is found that the four selected fitting formulas can meet the calculation requirements in terms of fitting values.According to the characteristics of the calculation method,the following conclusions are drawn:a)there is almost no correlation between the parameters in the formula,which proves that the parameters are independent;b)the numerical convergence of the magnetic coupling parameters in the formula is not good,and there is still modifiability in the optimization of the formula;c)there are differences between the optimal solution obtained by some formulas in the fitting process and the actual physical meaning.(4)In the chain complex system,the chain complexes constructed by cobalt ions were synthesized and tested.MCMC method is introduced to simulate the commonly used fitting formulas.Due to the special magnetic coupling interaction of this type of complex at low temperature,the theoretical fitting can not be used to fit the whole temperature range(2-300K).However,the MCMC method accurately locates the optimal fitting temperature,and achieves a very perfect convergence curve and the correlation between variables parameters in this temperature range.This is the first time that accurate piecewise fitting results have been obtained for the fitting calculation of magnetic coupling parameters.At the same time,because of the correlation of parameters,it also represents that the empirical formula can be further optimized.