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Abstract of [Hong99]

[Hong99]
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High-dimensional manganese(II) compounds with noncovalent and/or covalent bonds derived from flexible ligands: Self-assembly and structural transformation

Chang Seop Hong, Sang-Kil Son, Yoon Sup Lee, Moo-Jin Jun, and Youngkyu Do

Inorg. Chem. 38, 5602–5610 (1999)

[bib][BibTeX][link]doi:10.1021/ic990611w

A hydrogen- and covalent-bonded 3D array, [Mn(bpe)(H2O)4]n(ClO4)2n(bpe)4n(H2O)2n (2) [bpe=1,2-bis(4-pyridyl)-ethane], a covalent-bonded 3D network, [Mn(bpe)1.5(H2O)(tp)]n(H2O)n (3) [tp=terephthalate], and a covalent-bonded 2D sheet, [Mn(bpe)(N3)2]n (4), have been synthesized and characterized by spectroscopic data and singlecrystal X-ray diffraction studies. Complex 2 contains two types of packing bpe molecules: One type of bpe molecules (=N31-bpe and symmetry-related bpe) run along the chain direction, and the other type of bpe molecules (=N11-bpe and N21-bpe) are slanted to the chain linked by bridging bpe (=N1-bpe). The chain is coupled with hydrogen bonds via N31-bpe, while hydrogen bonds through packing bpe molecules of N11- and N21-bpe sew the chains, leading to a 3D interlocking network structure. The bpe ligands in 3 have an anti conformation for the bridging bpe and a gauche conformation for the capping bpe with a dihedral angle between the two pyridyl rings of 44.5°. The tp ligand acts as a linker of three metal ions through the unidentate and bridging modes, leading to the formation of a 2D layer. The final molecular dimensionality in 3 is determined from adding bpe ligands to the 2D sheet connected by tp ligands, resulting in a covalent-bonded 3D array where the bridging bpe ligands link the tp-bridged layers. The manganese(II) center in 4 consists of four equatorial azido nitrogen atoms and two axial bpe nitrogen atoms. The one-dimensional chains formed by two azido bridging ligands are interconnected by bpe ligands, each of which has two pyridyl rings with a dihedral angle of 67° leading to a two-dimensional sheet. Variable-temperature magnetic susceptibility data of 2 and 4 have been fitted to the infinite-chain model (H=–J ∑ SAi · SAi+1) derived by Fisher under the molecular field approximation (J´). Obtained exchange parameters are J=-0.083 cm-1, g=2.0 for 2 and J=-12.5 cm-1, g=2.0, J´=1.3 cm-1 for 4. In the case of 3, the magnetic nature was interpreted by the dimer model (H=–J S1·S2), affording parameters J=-0.96 cm-1, g=1.99, J´=-0.005 cm-1. MO calculations on a hypothetical dimeric unit (NH3)5Mn-bpe-Mn(NH3)5 are discussed to evaluate the magnetic nature for the bpe-bridged system 4.

Tags: molecular magnet, experiment, KAIST


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