Further synthetic investigation of the general lanthanoid(iii) [Ln(iii)]/copper(ii)/pyridine-2,6-dimethanol/carboxylate reaction system: {CuLn} coordination clusters (Ln = Dy, Tb, Ho) and their yttrium(iii) analogue.

In addition to previously studied {CuGd}, {CuGd}, {CuLn} and {CuLn} coordination clusters (Ln = trivalent lanthanide) containing pdm or Hpdm ligands (Hpdm = pyridine-2,6-dimethanol) and ancillary carboxylate groups (RCO), the present work reports the synthesis and study of three new members of a fifth family of such complexes. Compounds [CuLnO(OMe)(NO)(OCCHBu)(pdm)(MeOH)] (Ln = Dy, 1; Ln = Tb, 2; Ln = Ho, 3) were prepared from the reaction of Ln(NO)·xHO (x = 5, 6), CuX·yHO (X = ClO, Cl, NO; y = 6, 2 and 3, respectively), Hpdm, BuCHCOH and EtN (2 : 2.5 : 2 : 1 : 9) in MeCN/MeOH. Rather surprisingly, the copper(ii)/yttrium(iii) analogue has a slightly different composition, i.e. [CuYO(OMe)(NO)(OCCHBu)(pdm)(MeOH)] (4). The structures of 1·4MeCN·1.5MeOH and 4·2MeOH were solved by single-crystal X-ray crystallography. The five Cu and four Dy centres in 1 are held together by two μ-O, four μ-MeO, two syn,synη:η:μ BuCHCO, four η:η:η:μ pdm (each of these groups chelates a Cu atom and simultaneously bridges two Dy atoms through its two -CHO arms) and two μ-MeOH ligands. The four terminal nitrato groups each chelate (η:η) a Dy centre. The five Cu atoms are co-planar (by symmetry) forming a bow-tie arrangement; the four outer Cu atoms form a rectangle with edges of 3.061(1) and 6.076(1) Å. The four Dy centres also form a rectangle that lies above and below the plane of the Cu centres, with edges of 3.739(1) and 5.328(1) Å. The two strictly planar rectangles are almost perpendicular. Two trigonal bipyramidal μ-O groups link the perpendicular Cu and Dy frameworks together. The molecule 4 has a very similar structure to that of 1, differences being the replacement of the two chelating nitrato groups of 1 by two chelating BuCHCO ligands in 4 and the coordination polyhedra of the Ln and Y atoms (Snub diphenoids in 1 and biaugmented trigonal prisms in 4). Dc magnetic susceptibility data (χ) on analytically pure samples of 1-3, collected in the 300-2 K range, indicate that ferromagnetic exchange interactions dominate leading to large spin ground states. The χT vs. T data for 4 suggest moderately strong antiferromagnetic CuCu exchange interactions. Studies of the dynamic magnetic properties of the {CuLn} clusters show that 1 behaves as a SMM at zero field and 2 is a very weak field-induced SMM, while 3 exhibits only weak tails in the χ''vs. T plots at various ac frequencies at zero dc field.