Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit (I): UBLYP, UB3LYP, and UHF calculations

Abstract

Articles you may be interested inUnrestricted density functional theory based on the fragment molecular orbital method for the ground and excited state calculations of large systems Density functional theory with fractionally occupied frontier orbitals and the instabilities of the Kohn-Sham solutions for defining diradical transition states: Ring-opening reactions J. Chem. Phys. 111, 7705 (1999); 10.1063/1.480108Density functional study of intramolecular ferromagnetic interaction through m-phenylene coupling unit. III. Possibility of high-spin polymer Polyradicals comprised of m-phenylene-bridged organic radicals are well known as building blocks of organic ferromagnets, in which radical groups are connected with each other at the meta position in the benzene ring, and the parallel-spin configurations between radical sites are more stabilized than the antiparallel ones. Topological rules for spin alignments enable us to design organic high-spin dendrimers and polymers with the ferromagnetic ground states by linking various radical species through an m-phenylene unit. However, no systematic ab initio treatment of such spin dendrimers and magnetic polymers has been reported until now, though experimental studies on these materials have been performed extensively in the past ten years. As a first step to examine the possibilities of ferromagnetic dendrimers and polymers constructed of m-phenylene units with organic radicals, we report density functional and molecular orbital calculations of six m-phenylene biradical units with radical substituents and polycarbenes linked with an m-phenylene-type network. The relative stability between the spin states and spin density population are estimated by BLYP or B3LYP and Hartree-Fock calculations in order to clarify their utility for constructions of large spin denderimers and periodic magnetic polymers, which are final targets in this series of papers. It is shown that neutral polyradicals with an m-phenylene bridge are predicted as high-spin ground-state molecules by the computations, while m-phenylene-bridged ion-radical species formed by doping may have the low-spin ground states if zwitterionic configurations play significant roles to stabilize low-spin states. Ab initio computations also show an important role of conformations of polyradicals for stabilization of their high-spin states. The computational results are applied to molecular design of high-spin dendrimers and polymers. Implications of them are also discussed in relation to recent experimental results for high-spin organic molecules. d Standard geometries were assumed as CC and CH bond lengths and bond angles are 1.40 Å, 1.08 Å, and 120°, respectively. e J ab values by Eq. ͑11͒.

Synthesis, Structure, and Unexpected Magnetic Properties of La3Re2O10

“…[26][27][28][29][30] In all of these calculations, the triplet states were consistently below the energy of the singlets. This would imply that the magnetic interaction between two dimers should be ferromagnetic.…”

Chemical Indices of the Biomimetic Models of Oxyhemocyanin and Oxytyrosinase

“…However, spin-polarized DFT solutions in the LS states usually exhibit the broken symmetry problem (Isobe et al, www.intechopen.com 2002; Mitani et al, 2000a;Onishi et al, 2001;Salem, 1982;Takano et al, 2008;Takano et al, 2002a;Takano et al, 2001;Takano et al, 2000;Takano and Yamaguchi, 2007). Spin projection of the broken symmetry solutions should be carried out to eliminate the spin contaminations.…”

“…Chemical indices are useful criteria for the nature of chemical bonds. Since the broken symmetry solutions are employed in this study, several chemical indices, which are equally defined by the symmetry-adapted CASCI and CASSCF, are expressed in terms of the occupation numbers of DFT natural orbital (Isobe et al, 2003;Mitani et al, 2000a;Yamaguchi, 1990). These indices are used as common criteria for the nature of the chemical bonds of the Cu 2 (μ-η 2 :η 2 -O 2 ) core.…”

The Theoretical Study on the Spin States of the Perovskite-Type KCoF3 Solid

“…The local-spin-density-approximation (LSDA), which is one kind of the density functional theory (DFT), has often predicted that these insulators are metallic because of the strong correlation effect [3]. On the other hand, Hartree-Fock (HF) tends to overestimate the spin polarization (SP) effect [4]. In the spin-polarized hybriddensity functional theory (HUDFT) method, both correlation and SP effects have been modified and the reasonable calculation results have been provided for strong correlated transition metal clusters and magnetic molecules [1,2].…”