Synthesis, Structural Characterization, and Monte Carlo Simulation of the Magnetic Properties of Two New Alternating Mn^II Azide 2-D Honeycombs. Study of the Ferromagnetic Ordered Phase below 20 K

Reaction of Mn^II 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, P1̄ group (a = 9.269(2) Å, b = 9.635(3) Å, c = 18.860(4) Å, Z = 4), and compound 2 crystallizes in the monoclinic system, P2₁/c group (a = 14.416(3) Å, b = 8.515(2) Å, c = 15.728(4) Å, Z = 4). The two compounds show honeycomb structures based on dinuclear Mn−(μ-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−(μ_1,3-N₃)₂−Mn kind of bridges, compound 2 prefers the end-on Mn−(μ_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.