Investigation Of The Magneto-Structural Correlation Within 0, 1, Or 3 Dimensional Molecular Magnets Based On Cyano Groups, 1,10-phenanthroline, 8-quinolinato, Or Phosphorus Ions

Molecule-based magnetism designates an emerging field of research that focuses on the use of molecular approaches to design, synthesize, and study novel classes of magnetic materials where the properties can be tuned at the molecular level. So far, lots of molecule-based magnets have been reported, taking advantage of the versatility of molecular chemistry. The various structures of them give rise to different magnetic properties. Therefore, to systematically investigate the correlation between structures and magnetism is of profound significance to design the molecular magnets that would be applied on the molecular or spintronic devices. We report our systematical investigation and detailed discussion of the magneto-structural correlation within the 0, 1, and 3D molecular magnets mentioned below in this dissertation. The detailed investigation of the magneto-structural correlation reveals several rules from four magnetic systems, which would provide new clues to design and study unique molecular magnets for applications. The outline of this dissertation is as follows:1. Two complexes {[Co^Ⅱ（phen）₃][Co^ⅡI（phen）（CN）₄]₂}·phen·11H2O （1） and [Co^Ⅱ（μ-CN）2（Co^ⅡI）2（phen）4（CN）6]·C2H5OH·2H2O （2） were synthesized with identical starting materials but with a different order of addition. Their crystal structures, spectroscopic analysis, DFT calculations, and investigations of their magnetic properties are reported herein. The X-ray diffraction studies reveal that complex 1 mainly consists of discrete [Co^Ⅱ（phen）₃]²⁺ cations and [Co^ⅡI（phen）（CN）4]? anions, while complex 2 is dominantly comprised of discrete neutral V-shaped trinuclear units [Co^Ⅱ（μ-CN）2（Co^ⅡI）2（phen）4（CN）6]. The first low spin Co^Ⅱfragment with homoleptic 1, 10-phenanthroline ligands in 1 is observed at room temperature, owing to charge transfer from the neighboring anion via the adventitious contacts and anion-πinteractions. This is verified by structures, detailed theoretical analyses concerning frontier molecular orbital energy differences and Mulliken charge variations of the N atoms within the Co^ⅡN6 sphere, and magnetism. Meanwhile, such kind of supramolecular interactions are not found in complex 2, so it shows ordinary magnetic behaviors of the high spin Co^Ⅱion. Our investigations highlight that for a quantitative comprehension of spin-state energetic ordering in transition metal complexes, the supramolecular interactions must be taken into account in addition to the classical ligand field theory. Moreover, we find that the [Co^Ⅱ（phen）₃]²⁺ dication is sensitive to its surroundings in solid states, which is beneficial to the magnetic adjustment for the further synthesis of tunable molecular magnets and spin crossover systems.2. We report two solvent free Mq3 complexesα-Feq3 （3） andα-Crq3 （4）, the correlation between structures and magnetism of which is discussed for the first time among Mq3 complexes. To the best of our knowledge, this is the first case concerning the solvent free Feq3 and Crq3, thus they are entitled asα-Feq3 andα-Crq3, respectively. The phase transition occurs at around 400°C for complex 4, which is detected by the powder and single crystal X-ray diffraction. The initial magnetism investigation of both Mq3 reveals that complexes 3 and 4 show antiferromagnetic behaviors. The detail DFT studies show a clear correlation between assembly structures and the bulk magnetism that the larger the overlaps with the same signs of spin densities on stacking ligands, the more negative the value of the Weiss constant. Our investigations highlight that the spin density should be the dominant factor in analyzing the intermolecular magnetic interactions, which was rather difficult to figure out.3. We successfully synthesize two novel 8-quinolinato based and divalent metal ion containing antiferromagnetic 1D coordination polymers [FeIIMnII（8-quinolinato）4·（H2O）0.25]n （5） and [MnII（8-quinolinato）2]n （6）. By virtue of the rigidity of the 8-quinolinato ion, this is the first incorporation of 8-quinolinato ions into 1D magnetic chains. The hetero-spin 1D chains within complex 5 is in the rare···A-A-B-B···mode, while complex 6 possesses uniform homo-spin 1D chains. The variable-temperature magnetic susceptibility measurements of 5 and 6 indicate that the antiferromagnetic interactions exist between the magnetic centers, which have been estimated by using the modified Fisher-Drillon and Fisher theoretical models for 5 and 6, respectively. Complex 5 exhibits typical antiferromagnetic behaviors owing to the strong anisotropy accompanying with the position of the intrachain inversion centers, while complex 6 undergoes a spin-flop transition due to weak crystal anisotropy. The strengths of different kinds of supramolecular interactions within 5 and 6, which were difficult to compare, are evaluated using the theory of Atoms in Molecules.4. Herein, we report a novel manganese phosphate [MnII7（HPO₄）₄（PO₄）₂]n （7） with octa- and hepta-connection phosphate ions. This material only consists of manganese cations and phosphate anions without any other assistant mineralizers （H₂O, F^-, or Cl^-）, counterions （amines）, or template reagents （imidazole derivatives） for crystallization, whose crystalline solids are rather rare and difficult to obtain. Additionally, complex 7 with the phosphate ions of such high connectivity （octa- and hepta-connection） is record breaking among the first row transition metal phosphates. As a consequence of the high P-O-Mn connectivity, the 3D geometrically frustrated structure of complex 7 is observed, which offers multiple super-exchange paths and complex magnetic interactions. The detail magnetic investigation reveals that complex 7 shows canted antiferromagnetic （weak ferromagnetic） behaviors with double spin glass states, giving rise to the double relaxation at low temperatures, which is unprecedented in the manganese phosphates.