BIMETALLIC DERIVATIVES OF [M(EN)3]3- AN APPROACH TO INTERMOLECULAR MAGNETIC-INTERACTIONS IN MOLECULAR MAGNETS( IONS (M = CR, CO) )

The crystal and molecular structures together with the magnetic suscep tibilities of a series of [M(en)3]3+ (M = Cr, Co) derivatives are repo rted. The space group and unit cell dimensions of [Cr(en)3]3[FeCl6]Cl6 .H2O (1), [Co(en)3]3[FeCl6]Cl6.H2O (2), and [Cr(en)3] [FeCl4]Cl2.9H2O (3) are as follows: (1) R3, a = 15.445(4) angstrom, c = 21,060(6) angs trom, Z = 3; (2) R3, a = 15.346(3) angstrom, c = 20.880(5) angstrom, Z = 3; (3) P3c1, a = 11.654(3) angstrom, c = 15.508(4) angstrom, 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 bo nds connecting the iron and chromium (or cobalt) sublattices, the comp lex cations, anions, and water molecules are held together by ionic fo rces and by a three-dimensional network of hydrogen bonds. The magneti c 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 J(Fe-Cr)/k(B) = -0.153 K, J(Fe-Fe)/k(B) = -0.044 K, and J(Cr-Cr) /k(B) = -0.045 K, [Co(en)3][FeCl6] exhibits antiferromagnetic properti es below T(c) = 1.43 K and [Cr(en)3][FeCl6] evidences antiferromagneti c-like (compensated ferrimagnetic) ordering with (dchi/dT)max = 2.26 K . The data were interpreted in terms of the interaction Hamiltonia H = -2SIGMA(i<j)J(ij)S(i).S(j). Structural and magnetic properties are co rrelated 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 propa gate magnetic interactions in these molecular magnets.