Tuning the Structural and Magnetic Properties of Thermally Robust Coordination Polymers

Thermally robust materials of the M(5-X-pyrimidin-2-olate)2 type [M = Co, X = Cl (1Cl), X = Br (1Br), X = I (1I); M = Zn, X = Cl (2Cl), X = Br (2Br), X = I (2I)] have been synthesized. Their X-ray powder diffraction structural characterization has revealed that they crystallize as I4̄2d diamondoid frameworks, isomorphous to those of the pristine [M(pyrimidin-2-olate)2]n analogues (1H, M = Co; 2H, M = Zn). The magnetic measurements of the 1X series at magnetic fields of 100, 300, and 5000 Oe reveal a weak ferromagnetic ordering taking place below the Néel temperature (TN ∼ 20 K), arising from spin canting phenomena of the antiferromagnetically coupled cobalt centers. Moreover, magnetic hysteresis studies carried out on the 1X series at 2 K reveal a strong dependence of both the coercive field Hcoer (2500, 1000, 775, and 500 Oe for 1Br, 1Cl, 1I, and 1H, respectively) and the remnant magnetization Mrem (0.0501 μB for 1Br and 1Cl, 0.0457 μB for 1I, and 0.0358 μB for 1H) on the 5-substituent of the pyrimidin-2-olates. The molecular alloys [Co(5-Y-pyrimidin-2-olate)2] (Y = Cl/Br, 1Cl/Br) and [Co(5-Y‘-pyrimidin-2-olate)2] (Y‘ = Br/I, 1Br/I) have also been prepared and characterized, proving that they have intermediate properties. These materials combine interesting functional properties, such as chemical inertness, magnetism, photoluminescence, and (although weak) SHG activity.