Bimetallic Derivatives of [M(en)3]3+ Ions (M = Cr, Co): An Approach to Intermolecular Magnetic Interactions in Molecular Magnets

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Abstract

The crystal and molecular structures together with the magnetic susceptibilities of a series of [M(en)3]3+ (M = Cr, Co) derivatives are reported. The space group and unit cell dimensions of [Cr(en)3]3[FeCl6]Cl6·H 2O (1), [Co(en)3]3[FeCl6]Cl6·H 2O (2), and [Cr(en)3] [FeCl4]Cl2·9H2O (3) are as follows: (1) R3, a = 15.445(4) Å, c = 21.060-(6) Å, Z = 3; (2) R3, a = 15.346(3) Å, c = 20.880(5) Å, Z = 3; (3) P3c\\, a = 11.654(3) Å, c = 15.508(4) Å, Z = 2. The trigonal crystal structures contain discrete [M(en)3]3+ (M = Cr, Co), [FeCl6]3-, and Cl- ions and water molecules. With no covalent bonds connecting the iron and chromium (or cobalt) sublattices, the complex cations, anions, and water molecules are held together by ionic forces and by a three-dimensional network of hydrogen bonds. The magnetic susceptibilities of 1,2, [M(en)3] [FeCl6] (M = Cr, Co), and [Cr(en)3] [InCl6] are also reported. While 1 orders as a ferrimagnet at 0.91 K, with Jfe-Cr/kB = -0.153 K, JFe-Fe/kB = -0.044 K, and JCr-Cr/kB = -0-045 K, [Co(en)3] [FeCl6] exhibits antiferromagnetic properties below Tc = 1.43 K and [Cr(Cn)3][FeCl6] evidences antiferromagnetic-like (compensated ferrimagnetic) ordering with (dx/dT)max = 2.26 K. The data were interpreted in terms of the interaction Hamiltonia H = -2Σi<jJijSi·Sj. Structural and magnetic properties are correlated by investigating the superexchange pathways through which the magnetic moments interact and magnetic ordering is established. As a result, hydrogen bonds are shown to be an effective mechanism to propagate magnetic interactions in these molecular magnets. © 1994 American Chemical Society.

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