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• 作者：Timothy A. Hudson ; Kevin J. Berry ; Boujemaa Moubaraki ; Keith S. Murray ; and Richard Robson
• 刊名：Inorganic Chemistry
• 出版年：2006
• 出版时间：May 1, 2006
• 年：2006
• 卷：45
• 期：9
• 页码：3549 - 3556
• 全文大小：213K
• 年卷期：v.45,no.9(May 1, 2006)
• ISSN：1520-510X

文摘

Aqueous reaction mixtures containing citric acid, guanidinium carbonate, and a range of metal cations (Mg²⁺, Mn²⁺,Fe²⁺, Co²⁺, Ni²⁺, and Zn²⁺) at room temperature give crystalline products of composition [C(NH₂)₃]₈[(M^II)₄(cit)₄]·8H₂O (cit = citrate). In all cases, the crystals are suitable for single-crystal X-ray diffraction studies, which revealthat the compounds are isostructural (space group P4₂/n; a ~ 16.2 Å, and c ~ 11.5 Å). As was intended, cubane-like [M₄(cit)₄]^8- complex anions are present. The individual citrate units are chiral, but each cubane unit containstwo of one hand and two of the other, related around an S₄ axis. The cubane units are involved in no less than40 H-bonding interactions with guanidinium cations and lattice water molecules. Detailed susceptibility andmagnetization studies show that the intracluster magnetic coupling within the Mn^II, Fe^II, Co^II, and Ni^II cubanes isvery weak in all cases with J values of -0.82, -0.43, and -0.09 cm^-1 for the Mn, Fe, and Co species, respectively.A two-J model gave the best agreement with the susceptibility and high-field magnetization data for the Ni^II case,over the whole temperature range studied, and the sign of the parameters, J₁₂ = -0.3 cm^-1 and J₁₃ = +2.97cm^-1, correlated with the two Ni-(₃-O)-Ni angles observed in the cluster structure. All members of the 3d-block[M₄(cit)₄]^8- family have spin ground states, S_T, of zero, with the higher S_T levels just a few reciprocal centimetersaway in energy.