Further synthetic investigation of the general lanthanoid(III) [Ln(III)]/copper(II)/pyridine-2,6-dimethanol/carboxylate reaction system: {Cu(5)(II)Ln(4)(III)} coordination clusters (Ln = Dy, Tb, Ho) and their yttrium(III) analogue

摘要

In addition to previously studied {(Cu3Gd6)-Gd-II}, {(Cu8Gd4)-Gd-II}, {Cu(15)(II)Ln(7)} and {Cu(4)(II)Ln(8)} coordination clusters (Ln = trivalent lanthanide) containing pdm(2-) or Hpdm(-) ligands (H(2)pdm = pyridine-2,6-dimethanol) and ancillary carboxylate groups (RCO2-), the present work reports the synthesis and study of three new members of a fifth family of such complexes. Compounds [Cu(5)Ln(4)O(2)(OMe)(4)(NO3)(4)(O2CCH2But)(2)(pdm)(4)(MeOH)(2)] (Ln = Dy, 1; Ln = Tb, 2; Ln = Ho, 3) were prepared from the reaction of Ln(NO3)(3)center dot xH(2)O (x = 5, 6), CuX2 center dot yH(2)O (X = ClO4, Cl, NO3; y = 6, 2 and 3, respectively), H(2)pdm, (BuCH2CO2H)-C-t and Et3N (2 : 2.5 : 2 : 1 : 9) in MeCN/MeOH. Rather surprisingly, the copper(II)/yttrium(III) analogue has a slightly different composition, i.e. [Cu5Y4O2(OMe)(4)(NO3)(2)(O2CCH2But)(4)(pdm)(4)(MeOH)(2)] (4). The structures of 1.4MeCN center dot 1.5MeOH and 4.2MeOH were solved by single-crystal X-ray crystallography. The five Cu-II and four Dy-III centres in 1 are held together by two mu(5)-O2-, four mu-MeO-, two syn,syn eta(1):eta(1):mu (BuCH2CO2-)-C-t, four eta(2):eta(1):eta(2):mu(3) pdm(2-) (each of these groups chelates a Cu-II atom and simultaneously bridges two Dy-III atoms through its two -CH2O- arms) and two mu-MeOH ligands. The four terminal nitrato groups each chelate (eta(1):eta(1)) a Dy-III centre. The five Cu-II atoms are co-planar (by symmetry) forming a bow-tie arrangement; the four outer Cu-II atoms form a rectangle with edges of 3.061(1) and 6.076(1) angstrom. The four Dy-III centres also form a rectangle that lies above and below the plane of the Cu-II centres, with edges of 3.739(1) and 5.328(1) angstrom. The two strictly planar rectangles are almost perpendicular. Two trigonal bipyramidal mu(5)-O2- groups link the perpendicular Cu-5 and Dy-4 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 (BuCH2CO2-)-C-t ligands in 4 and the coordination polyhedra of the Ln(III) and Y-III atoms (Snub diphenoids in 1 and biaugmented trigonal prisms in 4). Dc magnetic susceptibility data (chi(M)) 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 chi T-M vs. T data for 4 suggest moderately strong antiferromagnetic Cu-II center dot center dot center dot Cu-II exchange interactions.