Nature of Magnetic Interactions in 3D {[MII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (M = Mn, Fe, Co, Ni) Molecular Magne

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• 作者：Dawid Pinkowicz ; Robert Peł ; ka ; Olga Drath ; Wojciech Nitek ; Maria Bał ; anda ; Anna Mał ; gorzata Majcher ; Giordano Poneti ; Barbara Sieklucka
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：August 16, 2010
• 年：2010
• 卷：49
• 期：16
• 页码：7565-7576
• 全文大小：1260K
• 年卷期：v.49,no.16(August 16, 2010)
• ISSN：1520-510X

文摘

The self-assembly of [Nb^IV(CN)₈]⁴⁻ with different 3d metal centers in an aqueous solution and an excess of pyrazole resulted in the formation of four 3D isostructural compounds {[M^II(pyrazole)₄]₂[Nb^IV(CN)₈]·4H₂O}_n, where M^II = Mn, Fe, Co, and Ni for 1−4, respectively. All four assemblies crystallize in the same I4₁/a space group and show identical cyanido-bridged structures decorated with pyrazole molecules coordinated to M^II centers. All four compounds show also long-range magnetic ordering below 24, 8, 6, and 13 K, respectively. A thorough analysis of the structural and magnetic data utilizing the molecular field model has allowed for an estimation of the values of coupling constants J_M−Nb attributed to the one type of M^II−NC−Nb^IV linkage existing in 1−4. The J_M−Nb values increase monotonically from −6.8 for 1 through −3.1 for 2 and +3.5 for 3, to +8.1 cm⁻¹ for 4 and are strongly correlated with the number of unpaired electrons on the M^II metal center. Average orbital contributions to the total exchange coupling constants J_M−Nb have also been identified and calculated: antiferromagnetic J_AF = −21.6 cm⁻¹ originating from the d_xy, d_xz, and d_yz orbitals of M^II and ferromagnetic J_F = +15.4 cm⁻¹ originating from d_z² and d_x²−y² orbitals of M^II. Antiferromagnetic interaction is successively weakened in the 1−4 row with each additional electron on the t_2g level, which results in a change of the sign of J_M−Nb and the nature of long-range magnetic ordering from ferrimagnetic in 1 and 2 to ferromagnetic in 3 and 4.