Strong Ferromagnetic Coupling of {[Cu（Hpht）（N3）]·H2O}n with Simultaneous End-on Azido and Carboxylato Bridges： a First Principle Study

The compound {[Cu(Hpht)(N_3)]·H_2O}_n (Hpht = hydrogen phthalate) is formedby chains of copper atoms bridged simultaneously by syn-syn carboxylato and end-on azido bridges.Taking into account the large Cu-O(1)-C(7) bond angle of the single carboxylato bridge (131°), orthe large Cu-N(11)-Cu bond angle of the azido bridge (111.9°), a moderately intrachainantiferromagnetic behavior should be expected for the compound. This paper is devoted to examiningthe apparently anomalous intrachain ferromagnetic behavior of {[Cu(Hpht)(N_3)]·H_2O}_n, using firstprinciples within the full potential linearized augmented plane wave (FP-LAPW) method. The totalenergy, the density of states (DOS), and the spin distributions are obtained. The atomic spindistribution has been analyzed as resulting from the interplay of electron delocalization and spinpolarization. The DOS reveals a surprisingly strong exchange interaction between the d type orbitalsof the copper and the π molecular orbitals of the two ligands.

ab initio Study of Electronic Structure and Magnetic Properties of a Novel Two-Dimensional Copper(II)-Radical Complex [Cu(NTTmPy)2(N3)2]n

The full-potential linearized augmented plane wave (FPLAPW) method with the generalized gradient approximations (GGA) is applied to study the compound [Cu(NTTmPy)2(N3)2]n (NITmPy = 2 - (3' - Pyridy1) -4, 4, 5, 5 - tetramethylimidazolin - 1 - oxy1 - 3 - oxide). The total density of states (DOS) and the partial density of states (pDOS) are calculated to explain the electronic and the magnetic properties of [Cu(NTTmPy)2(N3)2]n. It is found that [Cu(NTTmPy)2(N3)2]n is stable in the ferromagnetic state and the magnetic moment of the molecule mainly comes from the Cu atoms (0.518 μB) with partial contribution from N, O atoms of nitronyl nitroxide radicals. There exist orbital hybridization between 3d orbital of Cu and p orbitals of N(1) (from pyridyl rings of the NITmPy ligands) and N(4) (from azido group) and the weak direct exchange interactions between Cu and O atoms of nitronyl nitroxides. In addition, the bridging carbon atom (C(6)) carries a significant negative spin density (-0.019 μB). The sign alternation of the magnetic moment along zthe pyridyl ring is obtained, which agrees with experiments.