Tuning the Structural and Magnetic Properties of Thermally Robust Coordination Polymers

Abstract

Thermally robust materials of the M(5-X-pyrimidin-2-olate)2 type [M = Co, X = Cl (1(Cl)), X = Br (1(Br)), X = I (1(I)); M = Zn, X = Cl (2(Cl)), X = Br (2(Br)), X = I (2(I))] have been synthesized. Their X-ray powder diffraction structural characterization has revealed that they crystallize as I2d diamondoid frameworks, isomorphous to those of the pristine [M(pyrimidin-2-olate)2]n analogues (1(H), M = Co; 2(H), M = Zn). The magnetic measurements of the 1(X) series at magnetic fields of 100, 300, and 5000 Oe reveal a weak ferromagnetic ordering taking place below the Néel temperature (T(N) approximately 20 K), arising from spin canting phenomena of the antiferromagnetically coupled cobalt centers. Moreover, magnetic hysteresis studies carried out on the 1(X) series at 2 K reveal a strong dependence of both the coercive field H(coer) (2500, 1000, 775, and 500 Oe for 1(Br), 1(Cl), 1(I), and 1(H), respectively) and the remnant magnetization M(rem) (0.0501 mu(B) for 1(Br) and 1(Cl), 0.0457 mu(B) for 1(I), and 0.0358 mu(B) for 1(H)) on the 5-substituent of the pyrimidin-2-olates. The molecular alloys [Co(5-Y-pyrimidin-2-olate)2] (Y = Cl/Br, 1(Cl/Br)) and [Co(5-Y'-pyrimidin-2-olate)2] (Y' = Br/I, 1(Br/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.