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

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