Low-Dimensional Copper(II) Complexes with the Trinucleating Ligand 2,4,6-Tris(di-2-pyridylamine)-1,3,5-triazine: Synthesis, Crystal Structures, and Magnetic Properties

The preparation and structural characterization of three new copper(II) complexes of formula [Cu-3(dipyatriz)(2)(H2O)(3)] (ClO4)(6)center dot 2H(2)O (1), {(Cu-4(dipyatriz)(2)(H2O)(2)(NO3)(2)(ox)(2)](NC3)(2)center dot 2H(2)O)(n) (2), and [Cu-6(dipyatriz)(2)(H2O)(9)(NO3)(3)(ox)(3)] (NO3)(3)center dot 4H(2)O (3) [dipyatriz = 2,4,6-tris(di-2-pyridylamine)-1,3,5-triazine and ox = oxalate] are reported. The structure of 1 consists of trinuclear units [Cu-3(dipyatriz)(2)(H2O)(3)](6+) and uncoordinated perchlorate anions. The two dipyatriz molecules in 1 act as tris-bidentate ligands with the tiriazine cores being in a quasi eclipsed conformation, Each copper atom in 1 exhibits a distorted square pyramidal geometry CuN4O with four pyridyl-nitrogen atoms from two dipyatriz ligands building the basal plane and a water molecule occupying the axial position. The values of the intratrimer copper-copper separation are 8.0755(6) and 8.3598(8) angstrom. Compound 2 exhibits a layered structure of copper(II) ions which are connected through bis-bidentate dipyatriz ligands and bidentate/outer monodentate oxalato groups. The copper atoms in 2 exhibit six- [Cu(1)N4O2] and five-coordination [Cu(2)N2O3]. A water molecule and three pyridylnitrogen atoms [Cu(1)] and two pyridyl-nitrogen plus two oxalate-oxygen atoms [Cu(2)] define the equatorial plane whereas either an oxalate-oxygen and a pyridyl-nitrogen [Cu(1)] or a nitrate-oxygen [Cu(2)] fill the axial positions. The copper-copper separation through the bridging oxalato is 5.6091(6) angstrom whereas those across dipyatriz vary in the range 7.801(1)-9.079(1) angstrom. The structure of compound 3 contains discrete cage-like hexacopper(II) units [Cu-6(dipyatriz)(2)(H2O)(9)(NO3)(3)(ox)(3)](3+) where two trinuclear [Cu-3(dipyatriz)]6+ fragments are connected by three bis-bidentate oxalate ligands, the charge being balanced by three non-coordinated nitrate anions. The values of the intracage copper-copper distance are 5.112(3)-5.149(2) angstrom (across oxalato) and 7.476(2)-8.098(2) angstrom (through dipyatriz). Magnetic susceptibility measurements of polycrystalline samples of 1-3 in the temperature range 1.9-295 K show the occurrence of a weak antiferromagntic interaction across dipyatriz in 1 [J = -0.08(1) cm(-1), the Hamiltonian being defined as (H) over cap = -J((S-1) over cap center dot (S-2) over cap center dot (S-1) over cap center dot (S-3) over cap + (S-2) over cap center dot (S-3) over cap)] and weak ferro- (2) and strong antiferromagnetic (3) interactions through the oxalato bridge in 2 [J = +0.45(2) cm(-1)] and 3 [J = -390(1) cm(-1)). The use of the dipyatriz-containing copper(II) species as a building block to design homo- and heterometallic magnetic compounds is analyzed and discussed.