A new unique tetranuclear Cu(II) compound with double bridging thiocyanate anions:: Synthesis, X-ray structure and magnetism of [Cu4(μ1,3-NCS)6(dpyam)4(O2CH)2(H2O)2] (dpyam = di-2-pyridylamine)

A new unique tetranuclear copper(II) complex doubly-bridged by thiocyanate anions [Cu-4(mu(1.3)-NCS)(6)(dpyam)(4)(O2CH)(2)(H2O)(2) (dpyam = di-2-pyridylamine) has been synthesized and characterized by X-ray diffraction methods and magnetic measurements. The "outer" Cu ions, with a CuN3O(S,O) chromophore, have an axially elongated octahedral geometry. The basal plane of these outer Cu(II) ions consist of 2 nitrogen atoms of the dpyam ligand with Cu-N distances of 1.980(2) and 2.008(2) angstrom, one nitrogen atom of a bridging thiocyanate anion (Cu-N distance 1.961(3) angstrom) and an oxygen atom of a formiate molecule (Cu-O distance 1.977(1) angstrom). The axial positions are occupied by an oxygen atom of a water molecule (Cu-O distance 2.518(1) angstrom and by a sulfur atom of a bridging thiocyanate anion at a semi-coordination distance of 3.048(1) angstrom. The "inner" Cu atoms, with a CuN4(S-2) chromophore do also have an axially elongated octahedral geometry. The basal plane is formed by 2 nitrogen atoms of the dpyam ligand with Cu-N distances of 1.995(2) and 2.018(3) A and two nitrogen atoms of two bridging thiocyanate anions (Cu-N distances 1.946(3), 1.976(3) angstrom). The axial positions are occupied by two sulfur atoms of two bridging thiocynate anions (Cu-S semi-coordinating distances are 2.875(1) and 3.126(1) angstrom). Each Cu ion is bridged by two mu(1,3)-NCS anions (in an equatorial-axial bridging mode) forming in this way a zigzag tetranuclear unit. The magnetic susceptibility data of the compound have been investigated between 5 and 200 K. The compound shows a very weak antiferromagnetic interaction between the Cu ions, in agreement with the non-overlapping magnetic orbitals of each Cu ion. (c) 2005 Elsevier B.V. All rights reserved.