ABSTRACT
A 3D hybrid zinc formate framework, [NH(4)][Zn(HCOO)(3)], possessing an acs topology, shows a high degree of mechanical anisotropy and negative linear compressibility (NLC) along its c axis. High-pressure single-crystal X-ray diffraction studies and density functional theory calculations indicate that contraction of the Zn-O bonds and tilting of the formate ligands with increasing pressure induce changes in structure that result in shrinkage of the a and b axes and the NLC effect along c.
ABSTRACT
Hybrid inorganic-organic framework materials exhibit unique properties that can be advantageously tuned through choice of the inorganic and organic components and by control of the crystal structure. We present a new hydrothermally prepared 3D hybrid framework, [Mn(2-methylsuccinate)](n) (1), comprising alternating 2D manganese oxide sheets and isolated MnO(6) octahedra, pillared via syn, anti-syn carboxylates. Powder magnetic characterization shows that the compound is a homospin Mn(II) ferrimagnet below 2.4 K. The easy-axis is revealed by single-crystal magnetic susceptibility studies and a magnetic structure is proposed. Anisotropic elastic moduli and hardness, observed through nanoindentation on differing crystal facets, were correlated with specific structural features. Such measurements of anisotropy are not commonly undertaken, yet allow for a more comprehensive understanding of structure-property relationships.
ABSTRACT
A 2D homochiral inorganic-organic framework {[Mn(NPTA)(4,4'-bpy)(H(2)O)]·(H(2)O)(2)}(n) was prepared by assembling achiral polar 4-nitrophthalic acid, manganese ions, and ancillary 4,4'-bipyridine ligands (NPTA = 4-nitrophthalate) (4,4'-bpy = 4,4'-bipyridine). The isomorphous Zn(ii) compound was also prepared as a diamagnetic analogue. Adjacent manganese spin centres are linked by the syn-anti carboxylate to form a helical chain, and chains of the same chirality are connected by 4,4'-bpy ligands to generate a homochiral layered framework. Edge-to-face aromatic interactions between neighboring layers lead to a 3D homochiral supramolecular structure. Magnetization and heat capacity measurements indicate that the framework is a weak antiferromagnet at low applied field. The magnetic interactions between adjacent manganese ions in the helical chain can be fitted using the 1D Fisher model, with 2J/k = -0.68 K and g = 2.00. Moreover, the compound displays a unique field-dependent spin-flop transition in high magnetic fields, with a critical field of 23.6 kOe at 1.9 K.
