Three new polynuclear copper(II) complexes with the symmetric [Cu(mu1,1-N3)2Cu]2+ core and pyridine derivatives: syntheses, structure, and magnetic behavior.

Three new polynuclear copper(II) complexes, derived from the end-on azido bridging ligand and pyridine derivatives, have been synthesized, and their crystal structures have been determined by X-ray diffraction methods; they are the dinuclear compounds [Cu2(mu 1,1-N3)2(4-Etpy)4(mu-NO3)2] (1), and [Cu2(mu 1,1-N3)2(3-ampy)4(mu-NO3)2]. C2H5OH (2), and the trinuclear [Cu3(mu 1,1-N3)4(N3)2(Meinic)2(DMF)2] (3). 4-Etpy is 4-ethylpyridine, 3-ampy is 3-aminopyridine, and Meinic is methylisonicotinate. Compound 1, C28H36Cu2N12O6, crystallized in the monoclinic system, space group P2(1)/n, with a = 12.355(9) A, b = 12.474(4) A, c = 12.854(6) A, beta = 117.68(4) degrees, and Z = 2. Compound 2, C22H30Cu2N16O7, crystallized in the triclinic system, space group P1, with a = 9.695(2) A, b = 10.895(2) A, c = 7.909(2) A, alpha = 96.81(3) degrees, beta = 96.40(3) degrees, gamma = 96.56(3) degrees and Z = 1. Compound 3, C20H28-Cu3N22O6, crystallized in the monoclinic system, space group P2(1)/n, with a = 7.755(2) A, b = 14.680(5) A, c = 15.810(5) A, beta = 102.81(2) degrees, and Z = 2. 1-3 have the symmetric [Cu(mu 1,1-N3)2Cu]2+ core and structural parameters outside the previously reported range. Magnetic susceptibility data, measured from 2 to 300 K, show strong ferromagnetic coupling for the dinuclear end-on compounds 1 and 2 and bulk moderate ferromagnetic coupling for the trinuclear compound 3. These data were fitted to the appropriate equations derived from the Hamiltonian H = -JS1S2 for 1 and 2 and from the Hamiltonian H = -J1(SA1SB + SA2SB) - J2SA1.SA2 for 3, giving the parameters J = 230.1(1) cm-1, g = 2.17(0.01) for 1, J = 223.2(2) cm-1, g = 2.16(0.01) for 2, and J1 = 47.3(2) cm-1, J2 = -22.5(1) cm-1, gA = 2.26(0.02), gB = 2.07(0.03) for 3. The magnetic susceptibility data can be correlated with the structural parameters.

Synthesis, structural characterization, and Monte Carlo simulation of the magnetic properties of two new alternating MnII azide 2-D honeycombs. Study of the ferromagnetic ordered phase below 20 K.

Reaction of MnII and pyridine derivatives such as 4-methylpyridine (4-Mepy) and 4-ethylpyridine (4-Etpy) led to the new two-dimensional systems trans-[Mn(4-Mepy)2(N3)2]n (1) and trans-[Mn(4-Etpy)2(N3)2]n (2). Compound 1 crystallizes in the triclinic system, P1 group (a = 9.269(2) A, b = 9.635(3) A, c = 18.860(4) A, Z = 4), and compound 2 crystallizes in the monoclinic system, P2(1)/c group (a = 14.416(3) A, b = 8.515(2) A, c = 15.728(4) A, Z = 4). The two compounds show honeycomb structures based on dinuclear Mn-(mu-N3)2-Mn subunits linked to the four nearest-neighbor similar subunits by four end-to-end single azido bridges, but whereas the subunits of compound 1 show the end-to-end Mn-(mu 1,3-N3)2-Mn kind of bridges, compound 2 prefers the end-on Mn-(mu 1,1-N3)2-Mn fragment. Magnetically, compound 1 is an alternating 2-D system with two different antiferromagnetic interactions, whereas compound 2 corresponds to a two-dimensional ferro-antiferromagnetic system showing spin canting and permanent magnetization below 20 K. The coupling constant parameters J1 = -10.1 cm-1, J2 = -4.7 cm-1, and g = 2.019 for 1 and J1 = -5.3 cm-1, J2 = 2.9 cm-1, and g = 2.016 for 2 have been obtained from calculations using the Monte Carlo method based on the Metropolis algorithm.

Topological ferrimagnetic behavior of two new [Mn(L)2(N3)2]n chains with the new AF/AF/F alternating sequence (L = 3-methylpyridine or 3,4-dimethylpyridine).

The reaction of manganese(II) and pyridine derivatives such as 3-methylpyridine (3-Mepy) and 3,4-dimethylpyridine (3,4-Dmepy) led to the new one-dimensional systems trans-[Mn(3-Mepy)2(N3)2]n (1) and trans-[Mn(3,4-Dmepy)2(N3)2]n (2). Compound 1 crystallizes in the monoclinic system, space group P2(1)/n, a = 11.201(3) A, b = 14.499(4) A, c = 14.308(4) A, Z = 6, and compound 2 crystallizes in the triclinic system, space group P1, a = 11.502(4) A, b = 14.246(5) A, c = 16.200(8) A, Z = 6. The two compounds show the same general one-dimensional arrangement of double azido bridges between neighboring manganese atoms with the unprecedented -Mn-(mu(1,3)-N3)2-Mn-(mu(1,3)-N3)2-Mn-(mu(1,1)-N3)2-Mn- sequence. Susceptibility and magnetization measurements reveal a ferrimagnetic-like behavior derived from the topology of the chain. A model of the Heisenberg chain, comprising classical spins coupled through alternating exchange interactions J1J1J2... is proposed to describe the magnetic behavior.