Synthesis, Crystal Structure and Magnetic Characterization of a Series of CuII鈥揕nIII Heterometallic [Ln = La, Ce, Pr, Nd and Sm) Metal鈥揙rganic Compounds with an Unusual Single Cr

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• 作者：Pau D铆az-Gallifa ; Oscar Fabelo ; Laura Ca帽adillas-Delgado ; Jorge Pas谩n ; Ana Labrador ; Francesc Lloret ; Miguel Julve ; Catalina Ruiz-P茅rez
• 刊名：Crystal Growth & Design
• 出版年：2013
• 出版时间：November 6, 2013
• 年：2013
• 卷：13
• 期：11
• 页码：4735-4745
• 全文大小：528K
• 年卷期：v.13,no.11(November 6, 2013)
• ISSN：1528-7505

文摘

The synthesis and structural characterization of five Cu(II)鈥揕n(III) heteronuclear metal鈥搊rganic frameworks of formula {[Ln₄Cu₄(H₂O)₂₆(bta)₅]路mH₂O}_n and {[Ln₄Cu₄(H₂O)₂₄(bta)₅]路pH₂O}_n [Ln = Lap>IIIp> (1A/1B), Cep>IIIp> (2A/2B), Prp>IIIp> (3A/3B), Ndp>IIIp> (4A/4B) and Smp>IIIp> (5A/5B) with m/p = 20 (1A)/16 (1B), 18 (2A)/16 (2B), 14 (3A)/16 (3B), 22 (4A)/16 (4B) and 21 (5A)/14 (5B); H₄bta =1,2,4,5-benzenetetracarboxylic acid (1鈥?b>5)] have been performed. These compounds present a single-crystal to single-crystal phase transition from expanded A phases toward the B shrinking networks, which is triggered only in the presence of a dry environment. This phase transition is accompanied by a compression of the crystallographic b-axis in the range 2.4 to 2.8 脜 with the consequent decrease of the unit cell volume from 9.5% to 12%. The isomorphous crystal structures of 1A鈥?b>5A can be described as two crystallographically independent [Cu(II)鈥揕n(III)] heterometallic dinuclear units which are connected through two crystallographically independent btap>4鈥?/sup> ligands in the ac-plane, leading to 4,4-rectangular grids. These layers are connected along the crystallographic b-axis, through a pillaring btap>4鈥?/sup> group. The phase transition implies a change of the coordination mode of the btap>4鈥?/sup> pillar from bis-monodentate (1A鈥?b>5A) to tetrakis-monodentate (1B鈥?b>5B). Magnetic susceptibility measurements of polycrystalline samples of 1A鈥?b>5A in the temperature range 2.0鈥?00 K have in common the decrease of the 蠂_MT product with T which in the case of 1A is due to weak antiferromagnetic interactions between the copper(II) ions through the btap>4鈥?/sup> skeleton, the Lap>IIIp> cation being diamagnetic [J = 鈭?.5 cmp>鈥?p> with the Hamiltonian defined H = 鈭?i>JS_Cu1路S_Cu2]. For the 2A鈥?b>5A compounds, the additional exchange interaction between Cup>IIp> and the paramagnetic Lnp>IIIp> is masked by the crystal field effects (which partially removes the 2J + 1 degeneracy of the p>2S+1p>L_J free-ion ground state in zero magnetic field) (2A鈥?b>5A) and the thermal population of excited free-ion states (5A).