Role of Coordinated Water and Hydrogen-Bonding Interactions in Stabilizing Monophenoxido-Bridged Triangular CuIIMIICuII Compounds (M = Cu, Co, Ni, or Fe) Derived from N,N′-Ethylenebis(3-methoxysalicylaldimine): Syntheses, Structures, and Magnetic Properties

The syntheses, structures, and magnetic properties of the trinuclear triangular compounds [{(CuL1)-L-II}(2)Cu-II(H2O)(2)](ClO4)(2)center dot H2O (1) and [{(CuL1)-L-II}(2)M-II(H2O)(2)](ClO4)(2) {M = Ni (2), Co (3), Fe (4)} derived from N,N'-ethylenebis(3-methoxysalicylaldimine) (H2L1) are described. Compound I crystallizes in the monoclinic P2(1)/n space group, while the crystal system for the isomorphous compounds 2-4 is monoclinic P2(1)/c. In the cations of these compounds, two copper(II) ions occupy the salen type N2O2 cavity of two [L-1](2-) ligands, while one phenoxido and one methoxy oxygen atom of each of these two [(CuL1)-L-II] moieties coordinate to a central metal ion, which results in the formation of the trinuclear (Cu2MII)-M-II systems in which the two pairs of central...terminal metal ions are mono-phenoxido-bridged. In addition, to the two phenoxido bridges, the central metal ion is coordinated to two methoxy and two water oxygen atoms. The coordinated water molecules are strongly hydrogen bonded to the phenoxido and methoxy oxygen atoms. The presence of the coordinated water molecules and the interaction of these water molecules with the phenoxido and methoxy oxygen atoms are proposed to be the governing factors for the stabilization of the rare example of the monophenoxido-bridged Cu-3(II) compound 1 and of the first examples of the monophenoxido-bridged (Cu2MII)-M-II compounds 2-4. The three metal ions define an isosceles triangle. The phenoxido bridge angles in these compounds are significantly obtuse and vary between 121.10(12)degrees and 129.84(13)degrees. On the other hand, the trinuclear cores are highly twisted as evidenced from the range of the dihedral angles (58.5-143.7 degrees) between the basal planes of the terminal and the central metal ions. The variable-temperature (2-300 K) magnetic susceptibilities of compounds 1-4 have been measured. The magnetic data for 1 have been analyzed by using a model of two exchange integrals for the two pairs of adjacent metal ions, while one J value is considered for the other three complexes. The exchange integrals obtained are: Cu-3(II) compound 1: J(1) = -97.6 cm(-1), J(2) = -89.5 cm(-1); (Cu2NiII)-Ni-II compound 2: J = -25.4 cm(-1); (Cu2CoII)-Co-II compound 3: J = -9.0 cm(-1); (Cu2FeII)-Fe-II compound 4: J = -6.5 cm(-1). These moderate to weak antiferromagnetic interactions in 1-4 are related to the twisting of the trinuclear cores. The relative order of the exchange integrals can been understood from the nature of the magnetic orbitals. The structural and magnetic results have been compared with previously reported related compounds. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)