CONTROL OF INTRAMOLECULAR MAGNETIC INTERACTION BY THE SPIN POLARIZATION OF D(PI) SPIN TO P(PI) ORBITAL OF AN ORGANIC BRIDGING LIGAND

Multinuclear metal complexes have been designed with ferromagnetic interactions between the metal centers by considering the topological network of d pi spin to the bridging ligand. The four complexes [Cu-3(tpa)(3)-(ta)](ClO4)(3).4H(2)O (1), [Fe-2(bpepm)(NCS)(4)] (2), [Fe-2(bpmar)(H2O)(4)](NO3)(4).3H(2)O (3), and [Cu-2(bpmar)(NCS)(2)] (4), with tpa = tris(2-pyridylmethyl)amine, H(3)ta = trimesic acid, bpepm = 4,6-bis[(bis(2'-pyridyrethyl)-amino)methyl]pyrimidine, and H(2)bpmar = 4,6-bis [(N,N-bis(2'-pyridylmethyl)amino)methyl]-2-methylresorcinol, have been synthesized, and crystal structures of 1 and 2 have been determined. Magnetic properties have been investigated in the 2-270 K temperature range. Central metal ions in each complex are cupric for 1 and 4, high spin ferrous for 2, and high-spin ferric species for 3, respectively. Magnetic susceptibility measurements for 1, 2, and 4 showed antiferromagnetic behavior, and the Weiss constants for the data above 100 K are -3.26, -3.86, and -2.09 K, respectively. Magnetic data for 3 have been quantitatively studied above 10 K and have revealed that 3 exhibits ferromagnetic coupling with a magnetic exchange coupling constant of J = +0.65(3) cm(-1) (where H = -2S(1)S(2)). The measurement of magnetization (M) versus the field (H) for 3 has shown that the quantum number of the total angular momentum (J) at 4.0 and 8.5 K is larger than J = 4, where the expected value (J) in absence of ferromagnetic interaction is 5/2. The ferromagnetic interaction in 3 was interpreted by the spin polarization of d pi spin to the ligand p pi orbital. Crystal data: [Cu-3(tpa)(3)(ta)](ClO4)(3).4H(2)O (1), monoclinic, space group C2/c, a = 36.228(8) Angstrom, b = 19.565-(3) Angstrom, c = 26.341(6) Angstrom, beta 122.07(1)degrees, V = 15821(6) Angstrom(3), Z = 8, R = 0.090 (R(w) = 0.096) for 4992 data points with \F-o\ > 3 sigma(F-o); [Fe-2(bpepm)(NCS)(4)] (2), monoclinic, space group C2/c, a = 42.28(1) Angstrom, b = 13.467(4) Angstrom, c = 15.527(3) Angstrom, beta = 94.83(2)degrees, V = 8810(4) Angstrom(3), Z = 8, R = 0.050 (R(w) = 0.048) for 2676 data points with \F-o\ > 3 sigma(F-o).