Research On The Construction,Solid-liquid Structure Information Correlation,Assembly Process And Properities Of 3d Metal Cluster Based On N-Methyl Bis-Benzimidazole Ligand

The construction of 3d transition-metal clusters have been attracted much attention from scientists due to their fascinating structures and potential applications.Directional design and construction of clusters with multifunctions are the goals of scientists,which the chiral clusters are ideal candidates.Introducing chiral characteristics of structures into molecular materials would be of the desirable strategy for assembling the multifunctional molecule-based magnets.The departing point in this strategy is the conception of a chiral ligand with the desired coordination functions.Meanwhile,the knowledge of their formation of the clusters in the solution chemistry and the correlation of solid-liquid structure information ha ve important guiding significance for realizing controllable synthesis and constructing target functional products are also desirable.Based on chiral S,S-1,2-Bis-(1-methyl-1H-benzoimidazol-2-yl)ethane-1,2-diol(SS-H₂mbzimed)and non-chiral 1,2-Bis-(1-methyl-1H-benzimidazole-2-yl)-ethanol(Hmbzimed)ligands,a series of Co(II),N i(II),C u(I/II)and Zn(II)clusters have been constructed.The construction and magnetic properties of chiral seven nuclear Co/N i clusters were introduced in details.The assembling process of seven nuclear cobalt clusters has been studied by X-ray diffraction,ESI-MS and PXRD.At the same time,ESI-MS was used to preliminarily explore the solution behaviors and species information changes of a series of binuclear and tetranuclear clusters.The full text is divided into three chapters:The first chapter is the introduction.The research progress and application of polynuclear metal clusters are introduced.We introduce the research progress and applications of multifunctional polynuclear metal clusters,the research progress of chiral clusters,the research status and development of single-molecule magnets(SMMs)and chiral SMMs.At the same time,it also introduces the application and development of ESI-MS at home and abroad.It provides ideas and directions for the synthesis,assembly process,the change of molecula r fragments under electrospray ionization mass spectrometry and the preliminary exploration of magnetic properties.In chapter 2,the solvothermal reaction of cobalt/nickel sulfate with SS-H₂mbzimed,neutralized with triethylamine(Et₃N)in a mixture of methanol and water(2:1)resulted in triangular red crystals of[Co₇^II(L)₃(SO₄)₃(OH)₂(H₂O)₉]·4H₂O·3CH₃OH(Co₇)and triangular green crystals[N i₇^II(L)₃(SO₄)₃(OH)₂(H₂O)₉]·3H₂O(Ni₇).They are formed of chiral and polar clusters crystallizing in the R3 space-group.Co₇/Ni₇ consists of apex-shared asymmetric dicubane units where all the metals adopt octahedral coordination and the three ligands wrapped diagonally around the unit.One end of the cluster is bonded by six water molecules and the other end by three mono-dentate sulfates.The head-to-tail packing through extended H-bonds leads to polar chains.The ligands have lost two protons and adopt a cis-conformation which are coordinated to five metals around the waist of the dicubane and impose their c hirality onto the structure.Electrospray Ionization Mass Spectrometry(ESI-MS)of solution of the reaction as a function of time reveals the possible step-by-step assembly process of the cluster:[Co^II(HL)(SO₄)]^-?[Co₂^II(HL)(SO₄)₂]^-?[Co₄^II(HL)₂(OH)(CH₃OH)₂(SO₄)₃]^-?[Co₆^II(L)₂(OH)(C H₃O)(SO₄)₄]^-?[Co₇^II(L)₃(OH)₂(SO₄)₄]^2-.These results allow us to propose a possible process for the formation of Co₇ using crystallography,ESI-MS and PXRD,which reveal possibly the multidentate chelated of chiral ligand coordination driven orientation recognize step-by-step assembly process.This is a good example for chiral multidentate chelating ligand-controlled assembly of clusters.The product of the magnetic susceptibility and temperature(c_mT)of Co₇and Ni₇ are all exhibit ferromagnetic exchange couplings.Curie-Weiss fit of the susceptibility data above 150 K gives a Curie constant of 21.60 emu K/mol and Weiss temperature of+9.89 K for Co₇.Curie-Weiss fit of the susceptibility data above 150 K gives a Curie constant of 7.86emu K/mol and Weiss temperature of+20.62 K for Ni₇.Weiss temperatures are all above zero,therefore,the ferromagnetic coupling exchange phenomenon are confirmed.Ac-susceptibility reveals that Co₇ has significant frequency dependence with a blocking temperature below 5 K.The energy barrier and relaxation time are U_eff=9.4 k and?₀=4.8×10^-6s,which further confirms the behavior of single molecule magnets.However,the Ni₇ has no obvious frequency dependence at 2 K,may be exhibit the behavior of single-molecule magnets at lower temperatures.Chiral clusters with single-molecule magnet behavior are good candidates for exploring magnetic chiral dichroism and mulitfunctional clusters.In chapter 3,we report that the ligand of Hmbzimed with the metal salt Cu(NO₃)₂·3H₂O/Ni(NO₃)₂·6H₂O/Co(NO₃)₂·6H₂O/Zn(NO₃)₂·6H₂O in methanol by volatilization and solvothermal reaction to obtain compound 3[Cu₂(L)(CH₃O)(NO₃)₂](Cu₂)/4[Cu₂(L)₂(H₂O)₂]·2(NO₃)(Cu₂(?))/5[Cu₂^ICu₂^II(L)₄]·2(NO₃)(Cu₄)/6[N i₄(L)₃(OH)(NO₃)₄]·2(CH₃OH)(Ni₄)/7[Co₄(L)₄(CH₃O)₂]·2(NO₃)·Solv.(Co₄)and 8[Zn₄(L)₄(OH)]·3(NO₃)·Solv.(Zn₄).The solution behavior of Cu₂ single crystal mass spectrometry was analyzed.In positive mode,the strongest peaks were observed that the fragment[Cu₂^II(L)(NO₃)₃(CH₃O)]^-{Cu₂L}.In negative mode,the strongest peaks were[Cu₂^II(L)₂]²⁺{Cu₂L₂}.We attempted to volatilize the mother liquor of Cu₂synthesis,the blue block crystals were obtained,which were tested to be compound 4(Cu₂(?)).The ESI-MS of Cu₂(?)was found that the strongest peak also was[Cu₂^II(L)₂]²⁺{Cu₂L₂},which coincided with the strongest peak fragment of single crystal mass spectrometry of Cu₂ in positive mode.In addition,other high nuclear molecular fragments were observed,such as[Na Cu^ICu₃^II(L)₃(NO₃)(OH)₂(H₂O)₂]²⁺{Cu₄L₃}and[Cu₄^II(L)₃(NO₃)₄(CH₃O)₂(CH₃OH)]^-{Cu₄L₃}fragments,etc.On the basis of synthesizing Cu₂,the ligand of Hmbzimed was fully lose proton by changing the p H of the reaction system with the increase of Et₃N,and compound 5(Cu₄)was obtained.Although its structure is different from that of{Cu₄L₃}fragment,the ESI-MS of Cu₄were analyzed in positive mode that the strongest peaks were[Cu₄^II(L)₃(NO₃)₂(CH₃O)(Solv.)]²⁺{Cu₄L₃}.It is shown that Cu₄ is unstable under mass spectrometry and exists more stably in the form of{Cu₄L₃}.This is exactly similar to the{Cu₄L₃}fragment in Cu₂.This example demonstrates the importance of solid-liquid structure information correlation theory,and confirms that ESI-MS technology has guiding significance for the directional construction of clusters.The pressurized mass spectrometry of the neutral c luster Ni₄ shows with the increase of voltage,the strongest peak was[N i₂^II(L)₂(NO₃)]⁺{Ni₂L₂}in positive mode and the strongest peak in was[N i₂^II(L)(NO₃)₃(CH₃O)]^-{Ni₂L}in negeative mode.The combination of the two frements is just the neutral cluster Ni₄[N i₄(L)₃(NO₃)₄(CH₃O)]{N i₄L₃},which reflects the complementarity of the negative and positive modes.In addition,single crystal mass spectra of tetranuclear Cu₄,Co₄ and Zn₄ at different voltages(0-100 e V)were tested,and their stability,rich species information changes and possible splitting modes were analyzed.