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  • Author: Y. Elerman x
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Preparation, crystal structure and magnetic properties of a 3,5-dimethylpyrazolate bridged binuclear copper(II) complex [Cu2(L1)(3,5 prz)] (L1 = 1,3-Bis(2-hydroxy-1-napthylideneamino) propan-2-ol) (1) are reported. Variable-temperature magnetic susceptibility measurements for a powdered sample of the complex were carried out in the temperature range 5 - 350 K and analysed to obtain values of the parameter J in the exchange Hamiltonian H = -2JS1·S2 . In the dicopper(II) complex [Cu2(L2)(3,5 prz)], (L2 = l,3-Bis(2-hydroxy-5-chlorosalicylideneamino) propan-2-ol) (2) reported recently the antiferromagnetic interaction is much less than that of 1 (-27 = 440 cm-1 ), as result which is difficult to explain in terms of structural factors on the basis of widely accepted criteria. The differences in the magnetic behaviour now have been rationalized using the “ligand orbital complementary” concept

[Cu3 (L)3].3(C1O4) (LH = l,3-diaminopropan-2-ol) was synthesized and its crystal structure determined. It crystallizes in the triclinic space group P1̅ with a = 10.504(2), b = 10.856(2), c = 12.519(2) Å, a = 74.41(1), ß = 70.60(1), γ = 63.60(1)°, V = 1193.6(3) Å3, Z = 2. The structure consists of trimeric [Cu3(L)3]+3 units and three perchlorate anions in the asymmetric unit. In the compound three copper(II) ions are linked by 1,3-diamino-2-propanol molecules in such a way that an almost equilateral triangle is formed. The coordination spheres of the three copper(II) ions are slightly different from each other. The coordination geometry of Cu1 is a distorted square pyramid, and that of Cu2 is almost square planar while that of Cu3 is tetrahedrally distorted square planar. The copper(II) centers are separated by average 3.481(2) Å and antiferromagnetically coupled (-J = 100 cm-1), which follows from temperature- dependent magnetic susceptibility measurements in the temperature range 4.4 to 299 K. The average Cu-O-Cu angle is 128.1(1)° in the super-exchange pathway. As the temperature is increased, the magnetic moment rises from 1.41 μB at 4.4 K to 2.22 μB at 299 K. In the X(T ) curve no characteristic maximum was observed. The magnetic super-exchange interaction for the title compound is due to the effective overlap of the magnetic orbitals (dx²-y²) with orbitals of bridging alkoxide oxygen atoms

[Cu2(L3)(3,5-prz)] (L3 = 1,3-bis(2-hydroxy-4-methoxybenzylideneamino)-propan-2-ol) (3) was synthesized and its crystal structure determined. The compound consists of discrete binuclear units, in which copper atoms are linked by the alkoxide oxygen atom of the ligand and the pyrazolate nitrogen atoms. Variable-temperature magnetic susceptibility measurements for a powdered sample of the complex were carried out in the temperature range 4.4 - 308 K and analysed to obtain values of the parameter J in the exchange Hamiltonian H = -2JS1-S2. Recently, the dicopper(II) complexes [Cu2(L1)(3,5-prz)] (L1 = 1,3-bis(2-hydroxy-1-napthylideneamino)- propan-2-ol) (1) and [Cu2(L2)(3,5-prz)], (L2 = 1,3-bis(2-hydroxy-5-chlorosalicylideneamino)- propan-2-ol) (2) were reported. These compounds show antiferromagnetic behaviour (-2J: 444 cm-1 for 1 164 cm-1 for 2, and 472 cm-1 for 3). The strength of the super-exchange interaction (-2J) of 2 is much less than that of 1 and 3, a result which is difficult to explain in terms of structural factors on the basis of widely accepted criteria. The differences in the magnetic behaviour have been rationalized in terms of the bridging ligand orbital complementary / countercomplementary concept.

Preparation and magnetic properties of a 3,5-dimethylpyrazolate bridged binuclear copper(II) complex [Cu2(L)(3 ,5 -pyz)] (L = 1,3-Bis(2-Hydroxy-5-Chlorosalicylideneamino)propan- 2-ol) is reported. The crystal structure determined by X-ray diffraction methods. (C22H20N4O3CI2CU2), triclinic, space group P1̄, a = 9.622(3), b = 10.921(2), c = 11.420(3) Å, α = 100.73(2), β = 94.04(2), Υ = 108.08(2)°, V = 1110.2(5) Å3, Z = 2. Two copper(II) ions in a square-planar coordination are bridged via alkoxide oxygen and 3,5-dimethyl pyrozolate nitrogen atoms to form a dinuclear unit. The metal coordination sphere is four-coordinate, planar with an N2O2 donor set. The dihedral angle between the two coordination planes is 166.83°. There are significant intermolecular interactions between neighbouring binuclear entities. The shortest intermolecular Cu (1) ... Cu(1)i distance is 3.383(1) Å and the Cu(1) - O ( 1)i distance is 2.666(3) Å (i = 1 -x, -y, 1 - z). The variable-temperature magnetic susceptibility measurement for a powdered sample of the complex was carried out in the temperature range 5 - 350 K and analysed to obtain values of the parameter J in the exchange Hamiltonian ℋ = -2JScu Scu; 2J = -164 cm-1. The magnetic moment at 300 K is about 2.42 μB, and 0.22 μB at 5 K. The weak antiferromagnetism of the present complex is reasonably explained in terms of the orbital countercomplementary effect based on Hoffmann's theory for super-exchange interaction

Preparation, crystal structure and magnetic properties of a heterodinuclear complex, LCu(Me2CO)Gd(NO3)3 (L = (N,N′-bis(3-methoxysalicylidene)propane- 1,2-diamine) are reported. The crystal structure of the complex was determined by X-ray diffraction methods at 200 K. (C19H22N2O4 )Cu(C3H6O)Gd(NO3)3, monoclinic, space group P21/c, with a = 9.795(9), b = 18.763(3), c = 15.579(2) Å , β = 95.297(2) V = 2850.9(7) Å3 and Z= 4. The central region of the complex is occupied by Cu(II) and Gd(III) ions which are bridged by two phenolato oxygen atoms of the ligand. The copper ion adopts a square-based 4+1 coordination mode, the equatorial N2O2 donors being afforded by the ligand while the axial position is occupied by an oxygen atom of the acetone molecule. The Gd(III) ion is deca-coordinated. In addition to the two phenolate oxygen atoms, the coordination sphere contains two oxygen atoms of the OMe side arms of L and six oxygen atoms from the three bidentate nitrate ions. The Gd... Cu separation is 3.425(3) Å and the dihedral angle between the GdO(l)Cu and GdO(2)Cu planes is 164.8°. The magnetic susceptibility of the complex was measured over the range 5 - 350 K and the observed data were successfully simulated by the equation based on the spin-Hamiltonian operator (H = -JSCu · SGd), giving the exchange integral J(Cu-Gd) = 5.6(1) cm-1. This indicates a weak ferromagnetic spin exchange interaction. The nature of the magnetic super-exchange interaction of the title compound is compared with similar [Gd(III)-Cu(II)] heterodinuclear complexes.

[Cu2L(prz)] (prz = 3,5-dimethylpyrazole and L = 1,3-bis(5-bromo-2-hydroxybenzylidene)- propan-2-ol) was synthesized and its crystal structure determined. It crystallizes in the orthorhombic space group Pbca with a = 14.160(9), b = 15.109(4), c = 21.298(5) Å, V = 4557(1) A3, Z = 8 . Two copper(II) ions are in a square-planar coordination. The metal coordination sphere is four-coordinate, with a planar N2O2 donor set. The dihedral angle between the two coordination planes is 12.14(7)°. The copper(II) centers are separated by 3.365(1) Å and antiferromagnetically coupled (J = -214.3 cm-1), which follows from temperature-dependent magnetic susceptibility measurements in the temperature range 4.6 to 310 K. The Cu-O-Cu angle is 125.9(1)° in the super-exchange pathway. The magnetic moment at 310 K is ca. 1.76 B.M. and 0.13 B.M. at 4.6 K.