| Molecule-based magnetism designates an active and interdisciplinary research field thatfocuses on the use of molecular approaches to design, synthesize, and study the composition,structure, properties and structure-property relationships of the magnetic materials. Until now,lots of molecule-based magnetic materials have been reported owing to the flexibility ofmolecular chemistry. The various structures of magnetic materials have demonstrateddifferent magnetic behaviors, such as spin-flop, metamagnetism, spin-canting, spin-frustration,spin-glass, single-molecule magnets (SMM), single-chain magnets (SCM), etc. The trends ofresearch based on the molecule-based magnetic materials can be classified into the followingfour main classes:(i) molecule-based magnets with higher critical temperatures;(ii)multifunctional magnetic materials, such as magneto-electronic coexist, magnetic chiral, andporous material for magnetic separation;(iii) non-thermally stimulated magnetic materials,such as light-induced/stress-induced/electric induced magnet.In order to obtain novel molecule-based magnetic materials and porous magneticmaterials, we have chosen different polydentate ligands Schiff base ligand N,N’-bis(salicylidene)hydrazine (H2salhn),1,1,1-tris(hydroxymethyl)propane (H3tmp),4-methyl-3-nitrobenzoic acid (HL), phosphite, and/or4-(tris(hydroxylmethyl)methyl)pyridine(4-thmpyH3) to react with transition metal ions to obtain thirteen compounds. We haveanalyzed the effects of solvent, temperature, pH, and ancillary ligands on the structures of thecompounds. The structure-property relationships have been summarized by systematicalinvestigation and detailed discussion of the magnetic and porous properties. The outline ofthis dissertation is as follows:1. Two novel complexes,[CoIICoIII4(salhn)4(N3)6(MeOH)2(H2O)2]·4MeOH·2H2O (1) and[CuII2(salhn)(N3)2]n(2)(H2salhn=N, N’-bis(salicylidene)hydrazine), were synthesized andstructurally characterized by X-ray single-crystal diffraction. Complex1is a zigzag-likepentanulear [CoIICoIII4] cobalt cluster, while complex2consists of a1D coordination complexcontaining subunit [CuII2(salhn)(N3)2]. Compounds1and2both possess end-on (EO, μ-1,1)azide bridging. The magnetic measurements indicate that both1and2showantiferromagnetic behaviors. Complex2displays a phase transition with a critical field of0.02T at2.0K. Compared with the previous Co2(salhn)3diamagnetic system andCu2(salhn)2(H2O)4system, we have successfully obtained two extended networks withantiferromagnetism by employing the azide ligand, which play a guiding role for the future ofexperimental research.2. Solvothermal reactions of1,1,1-tris(hydroxymethyl)propane (H3tmp) and FeCl3using different counterions resulted in three hexanuclear iron(III) clusters(C5N2H14)[Fe6(μ6-O)Cl6(tmp)4]·2H2O·CH3OH (3),(C3N2H5)2[Fe6(μ6-O)Cl6(tmp)4](4), and(C4N3H8)3(C2N3H4)[Fe12(μ6-O)2Cl12(tmp)8]·3(CH3OH)(5), then their structures andmagnetic properties were characterized. The tripodal alcohols ligands are very useful inconstructing magnetically high-nuclearity metal clusters. In all cases, similar anionic cluster[Fe6(μ6-O)Cl6(tmp)4]2-is formed by six Fe(III) ions, four tmp3-ligands, one center O2-ion,and six Cl-ions. Magnetic studies indicate that these three compounds show slightly differentmagnetic data, despite they display similar magnetic features. The dipolar interactions and thehydrogen-bond interactions may be responsible for such differences.3. Three novel one-dimensional (1D) lanthanide coordination complexes involving the4-methyl-3-nitrobenzoic acid (HL) ligand, with the general formula [Gd(L)3(H2O)(CH3OH)](6),[Gd(L)3(H2O)2]·(4,4’-bpy)·CH3OH (7),[Dy(L)3(H2O)(CH3OH)](8), have beensynthesized by the solvothermal reactions. These complexes have been structurallycharacterized by single-crystal X-ray diffraction, IR, PXRD, TGA, and elemental analyses.Compounds6-8were obtained under the condition of the mixed solvent. We want to employpure solvent conditions to investigate whether the mono-solvent coordinated complex can beassembled or not. Unfortunately, single crystals could not be obtained when the reactionsolvent was employed pure water or methanol. Complexes6and8are isostructural except thedistinction of metal ion. Magnetic measurements indicate that complexes6and7both showparamagnetic behaviors, but complex8shows antiferromagnetic behavior. Complex8behaves slow relaxation of the magnetization, where the frequency-dependent out-of-phasesignals are noticed. However, the characteristic maxima were not reached above2K underzero direct current (DC) fields. When a DC field of5000Oe was employed, the frequencydependent peaks of alternating current (AC) signals were obtained.4. Four new compounds,[Ni(HPO3)(4,4’-bpy)(H2O)3]·4H2O (9),[Co2(HPO3)2(4,4’-bpy)2(H2O)6]·9H2O (10),[Zn(HPO3)(4,4’-bpy)0.5]·H2O (11), and[Co3(PO3)2(4,4’-bpy)3(H2O)6]·3H2O (12), have been synthesized. Compounds9-11wereformed under the condition of the unsealed filtrated solution leading to the fast evaporationrate. we change the process of our experiment, i.e., seal the filtrated solution for each, toreduce the rate of the evaporation of the filtrated solution. As expected, new crystal, i.e.,complex12, has been formed with different color and shape from10. However, no newcrystals have been obtained from the systems9and11, which indicate that the differentevaporation rate is feeble for the systems9and11. Compounds9and10are linear chains andisostructural except for the distinction of the metal ion and the number of lattice watermolecules. Compound11consists of2D sheet structure. For compound12, phosphite PO33-group acts as η1:η1:η1:μ3mode linking three Co ions forming Kagomé framework with1Dhexagonal channels along the c axis. Magnetic measurements indicate that compound9shows paramagnetic behavior, while compound10displays antiferromagnetic behavior. Compound12exhibits the antiferromagnetism with a pronounced field-induced spin-flop transition. Acritical field of3T at2.0K is determined from the derivative dM/dH curve. Meanwhile,compound12shows a strong spin-frustration arising from the geometric frustration inkagomé lattice. The dehydrated phase12a displays a characteristic of N2-adsorption withtype-II isotherm. We performed detailed magnetic measurements for12a, which exhibits quitedifferent magnetic properties from12. Compound12a displays a ferrimagnetic behavior witha lower transition field of0.2T, and a weaker spin-frustration. The results showed that themagnetic properties of the system can be tuned by the hydrogen bonding interactions betweenthe guest molecules and the host framework. Furthermore, slower evaporation rate of thesolvent may result in more complete of coordination.5. We have synthesized a microporous magnetic framework based on the tripodal alcoholderivative with pyridyl group4-(tris(hydroxymethyl)methyl)pyridine (4-thmpyH3) ligand,[Co10O(4-thmpy)4(CH3COO)3(H2O)6(CH3O)3]·8CH3OH (13), which contains supertetrahedraldeca-metallic cobalt clusters as nodes and4-thmpy3-ligands as linkers to form a NaCl-likenetwork. The complex shows a canted antiferromagnetism with spin-glass behavior. There ishydrogen bonding between the guest methanol molecules and the framework in compound13.The removal of guest molecules might lead to the slight change of the framework, whichbenefits the spontaneous magnetization at higher temperature. Nonetheless, the spin-cantingand spin-glass behaviors are still maintained. The permanent porosity was evaluated by N2adsorption measurement, which exhibits a typical type-I curve. The complex mainly showshydrophobic nature validated by CH3OH and H2O adsorption measurements that is consistentwith the grand canonical Monte Carlo (GCMC) theoretical simulation. It is observed that theCH3OH molecule locates inside the hole and forms short contacts with the pyridine ring(C-H···π=2.879). We have obtained microporous magnetic materials by using semirigidligand, which provide another theoretical and experimental basis for the future synthesis ofporous magnetic. |
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