Synthesis, Structures, and Properties of Metal Formates



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Metal-organic frameworks (MOFs) are inorganic-organic hybrid materials containing metal cations connected with organic bridging ligands to form extended structures. The research present in this dissertation investigates the use of short-bridging ligands in constructing dense-MOFs under solvothermal conditions and their applications. In particular, formate, the smallest carboxylic ligand was used as the organic bridging ligand. Using different metals in building MOFs enables the introduction of different properties. The temperature and reaction time proved to be the key factors in synthesizing pure phases. A series of layered divalent metal formate compounds, [M(HCOO)2.(HCONH2)2] (M=Mn[2.1], Ni[2.2], Cu[2.3], Zn[2.4], Mg[2.5]), were synthesized and characterized. Order-disorder phase transformations were observed in [2.1], [2.2] and [2.4]. The magnetic properties of the three magnetic members, [2.1], [2.2] and [2.3] revealed that all the compounds are antiferromagnetic Heisenberg square lattices with S=5/2 , 1, and 1/2 respectively, with low temperature long range order (LRO). The second series of transition metal formates, [CH(NH2)2][M(HCOO)3] (M= Mn[3.1], Fe[3.2], Co[3.3], Ni[3.4], have 3D-framework structures. The compound [3.1] has phase transitions above and below room-temperature. Dielectric anomalies were observed in the vicinity of the phase transitions and the low temperature transition appears to be ferroelectric in character. All four compounds are spin-canted antiferromagnets with Mn, Fe, and Co members showing spin reorientations in the LRO state. Fifteen lanthanide formate frameworks were also synthesized, nine were isostructural with the composition Ln(HCOO)3.(HCONH2)2 (Ln=Y[4.1], Sm[4.2], Eu[4.3], Gd[4.4], Tb[4.5], Ho[4.6], Tm[4.7], Yb[4.8] and Lu[4.9]) and six were isostructural with the composition [CH(NH2)2][Ln(HCOO)4](Ln=Y[4.10], Sm[4.11], Ho[4.12], Tm[4.13], Yb[4.14] and Lu[4.15]). The luminescence properties of [4.2], [4.3], [4.5] and [4.11] were investigated and show characteristic emission bands. Finally, an environmentally friendly rare earth (lanthanides) recycling method based on metal-formate frameworks is described. We have discovered that oxides containing rare earths readily react with formamide and form lanthanide-formate frameworks. The chemistry has been extended to more complex oxide mixtures found in commercially available phosphors and rare earth containing waste materials. The method can eliminate the need for use of strong acids and the subsequent waste disposal problems that ensue in the current established methods.



Metal-organic frameworks, Metal formates, Formates, Transition metals, Lanthanides, 2D magnets, Multiferroics, Luminescence, Rare earths, Rare earth recycling, Solvothermal


Portions of this document appear in: Samarasekere, Pradeep, Xiqu Wang, Allan J. Jacobson, Joshua Tapp, and Angela Möller. "Synthesis, Crystal Structures, Magnetic, and Thermal Properties of Divalent Metal Formate–Formamide Layered Compounds." Inorganic chemistry 53, no. 1 (2013): 244-256.