Structural Adaptation of Ni4O4 Units To Form Cubane, Open Dicubane, Dimeric Cubane, and One-Dimensional Polymeric Cubanes: Magnetostructural Correlation of Ni4 Cluster

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• 作者：Debarati Das ; Goutam Mahata ; Amit Adhikary ; Sanjit Konar ; Kumar Biradha
• 刊名：Crystal Growth & Design
• 出版年：2015
• 出版时间：August 5, 2015
• 年：2015
• 卷：15
• 期：8
• 页码：4132-4141
• 全文大小：630K
• ISSN：1528-7505

文摘

The complexation reactions of a tripodal chelating ligand, [3,5-bis(2-amino-ethyl)-[1,3,5]triazinan-1-yl]-methanol (L), which is produced by the in situ transformation of 1,3,6,8-tetraazatricyclo[4.4.1.1^3,8]dodecane (L¹) with Ni(NO₃)₂路6H₂O has been explored in the presence of ammonium salts of inorganic and organic anions. These reactions resulted in four crystalline complexes [Ni₄(L)₂(渭₃-OH)₂(NCS)₄]路4H₂O (1), [Ni₄(L)₂(渭₂-N₃)₄(N₃)₂]路2H₂O (2), [Ni₈(L)₄(渭₃-OH)₄(BDC)₃(H₂O)₄]路BDC路28(H₂O) (3, BDC = 1,4-benzene dicarboxylate) and {[Ni₄(L)₂(渭₃-OH)₂(NDS)₂(H₂O)₂]路NDS路11(H₂O)}_n (4, NDS = naphthalene-1,5-disulfonate). The crystal structure analyses of 1鈥?b>4 reveal that all contain Ni(II) clusters, which act as secondary building units to generate higher order aggregates. The complexes 1, 3, and 4 contain exclusively Ni₄ cubane units: a discrete cubane in 1, a dimer of cubanes linked by BDC in 3, and cubanes linked in one dimension by NDS to form a 1D-coordination polymer in 4. Interestingly, complex 2 exhibits an open dicubane with two missing vertices. Although a plethora of water molecules had been included in their crystal lattices, the crystals were found to be stable even at room temperature. The water molecules govern the overall crystal packing by the formation of strong hydrogen bonds and clusters. Large clusters of water such as (H₂O)₂₈ and (H₂O)₁₆ were observed in 3 and 4, respectively, while dimers of water were observed in 1 and 2. Magnetic susceptibility (蠂_M) measurements in the temperature range of 2鈥?00 K on 1鈥?b>3 reveal that the metal centers are ferromagnetically coupled in all three depending on their respective exchange pathways. Interestingly, the room temperature (300 K) 蠂_MT values increase as the molecular aggregation increases from discrete cubane (5.5 cm³ K mol^鈥?) to face sharing open dicubane (6.21 cm³ K mol^鈥?) to connected dicubane (11.36 cm³ K mol^鈥?). The modes of bridging by ^{鈥?/sup>OH, N₃鈥?/sup>, and BDC and their bond angles with paramagnetic Ni(II) centers clearly explained the overall ferromagnetism operating in the spin clusters.}