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Intercalation Chemistry in Misfit Transition Metal Chalcogenides

Intercalation Chemistry in Misfit Transition Metal Chalcogenides
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대학원 화학과
Intercalation ChemistryMisfit TransitionMetal Chalcogenides
이화여자대학교 대학원
저차원 화합물 중 최근에 알려진 새로운 유형의 intercalation 화합물인 misfit compounds의 특이한 결정 구조에 대해 연구하였다. X-ray diffraction을 Rietveld full refinement에 의해 분석한 결과 PbTiS_(3) 화합물의 TiS_(2) layer는 space group이 C2_(1)/m이고 a = 3.409 A°, b = 5.880 A, c = 11.760 A°, α = 95.29° 를 갖고 PbS는 space group이 C2/m으로 a = 5.800 A°, b = 5.881 A°, c = 11.759 A°, α = 95.27°의 monoclinic structure을 갖는다. PbTi_(2)S_(5)는 TiS_(2)의 경우 space group이 C2_(1)/m이고 a = 3.396 A°, b = 5.866 A°, c = 17.410 A°, α = 93.60°를 가지며, PbS는 space group이 C2/m으며 a = 5.755 A°, b = 5.869 A°, c = 17.350 A°, α = 93.74°으로 또한 PbTiS_(3)와 같은 monoclinic structure임을 확인할 수 있었다. Incommensulate한 a parameter의 비는 두 화합물 모두 대략 1.699로서 irrational 하지만 5/3에 가까운 값을 보였다. 각 화합물의 배열을 살펴보면, PbTiS_(3) 화합물은 rock salt 구조인 PbS layer와 CdI_(2)-tyPe의 구조를 갖는TiS_(2) layer가 번갈아 있는 ...HCHC.... 구조를 갖고 PbTi_(2)S_(5) 화합물은 PbTiS_(3)화합물 구조에 CdI_(2)-type의 구조 TiS_(2)가 층간 삽입되어진 ...HHCHHC...packing 구조를 가지며 열역학적으로 안정된 packing을 하기위해 서로 distort 되면서 층간의 독특한 local symmetry를 가짐을 알 수 있었다. Misfit 화합물에서 MS 층의 화학적 역할을 알아보기 위하여 동일한 CdI_(2)-type의 TiS_(2) 층을 갖는 PbTi_(2)S_(5), BiTi_(2)S_(5), TiS_(2)에 amine과 cobaltocene을 intercalate시키고 비교하였다. TiS_(2)에서는 butylamine이 층상 구조에 평행하게 배열되도록 intercalate 되었으나 BiTi_(2)S_(5)에서는 intercalate 되지 않았고, PbTi_(2)S_(5) 에서는 intercalate 된 phase 가 minor phase로 존재하였다. 즉 butylamine에 대한 intercalation 성질은 TiS_(2), PbTi_(2)S_(5), BiTi_(2)S_(5) 순으로 약해졌다 이것은 BiTi_(2)S_(5)에서는 Bi_(2+)가 6p_(1) configuration을 가지므로 BiS 층으로 부터 dichalcogenide 층으로 charge transfer가 일어나 Lewis base의 Intercalation이 저해되지만 Pb가 6p^(0)인 PbS 층에서는 charge transfer가 일어나지 않기 때문이라 믿어진다. 따라서, misfit 화합물의 intercalation 반응은 MS 층의 중심 금속의 electronic structure에 따라 MS 층으로 부터 TX_(2)층으로의 charge transfer 여부에 따라 달라지는 것으로 믿어진다. Cobaltocene을 intercalate 시켰을 때는 세 host 모두 실제 cobaltocene의 van der Waals dimension 보다 작은 5.6-5.7A°의 c축 증가를 보였고, host-guest 간의 charge transfer 보다는 중성 cobaltocene 분자와 TiS_(2) 층의 sulfur 간의 약한 interaction에 의해 intercalation이 일어나고, 이 때 misfit 화합물의 층간 charge transfer 유무는 반응성에 크게 영향을 주지 않았다.;Some misfit compounds with a unique crystal structure which are recently known as a new low dimensional structure type have been studied. The result of X-ray diffraction by Rietveld full refinement indicates that a misfit layered compound, PbTiS_(3), could be discribed as a two-phase intergrown system. The first phase, TiS_(2) sublattice, has a C2_(1)/m space group symmetry, and its unit cell dimensions are a = 3.409 Å, b = 5.880 Å, c = 11.760 Å and α = 95.29°. The second system, PbS sublattice, has a C2/m space group symmetry and a basic structure unit cell given by a = 5.800 Å, b = 5.881 Å, c = 11.759 Å and α = 95.27°. PbTi_(2)S_(5) is a misfit layered compound in which two types of slab, PbS and 2(TiS_(2)) are packed alternately along the c direction. The TiS_(2) slab in PbTi_(2)S_(5) has a C2_(1)/m space group and the unit cell paramerter is a = 3.396Å, b = 5.866Å, c = 17.410Å and α = 93.60°. The PbS slab with a C2/m space group has a unit cell given by a = 5.755Å, b = 5.869Å, c = 17.350Å and α = 93.74°. The misfit between the two slabs occurs along the a direction. The ratio of each a parameter is about 1.699, which is irrational but close to 5/3. The structure of the PbTiS_(3) compound is composed of an alternately packed two-atom-thick PbS layer with a distorted NaCl-type structure and an unit of TiS_(2) layers with a distorted CdI_(2)-type structure. A different ratio has also been found in PbTi_(2)S_(5) in which two successive TiS_(2) slabs were separated by a PbS layer. In order to find out the chemical role of the MS layer in the misfit compounds, some amines and cobaltocene were intercalated in PbTi_(2)S_(5), BiTi_(2)S_(5) and TiS_(2). The reactivity of amine intercalation decreased in the sequence of TiS_(2), PbTi_(2)S_(5) and BiTi_(2)S_(5). The difference of reactivities can be explained by the charge transfer between the slabs. In BiTi_(2)S_(5), the charge transfer from the MS layer to the TiS_(2) layer occurs by overlapping the patially filled Sp orbital of Bi^(2+) with the empty 3d orbital of titanium. It is more difficult to intercalate Lewis base in the negatively charged TiS_(2) slab of BiTi_(2)S_(5) than in TiS_(2). In PbTi_(2)S_(5), since Pb^(2+) has the 6s26ps configuration, it is believed that there is no charge transfer. When the cobaltocene is intercalated In the three different host materials, the reaction occurs by weak interactions between neutral cobaltocene molecule and sulfurs of the TiS_(2) slab rather than the charge transfer. The existence of the charge transfer didn't considerably affect the reactivity of cobaltocene intercalation.
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