Rationalization of the behavior of M₂(CH₃CS₂)₄I (M = Ni, Pt) chains at room temperature from periodic density functional theory and ab initio cluster calculations

Abstract

The electrical conductivities and plausible charge-ordering states in the room temperature (r.t.) phase for MMX chains [Ni(2)(dta)(4)I](∞) and [Pt(2)(dta)(4)I](∞) (dta = CH(3)CS(2)(-)) have been analyzed with periodic density functional theory (DFT) and correlated ab initio calculations combined with the effective Hamiltonian theory. Periodic DFT calculations show a more delocalized nature of the ground state in [Pt(2)(dta)(4)I](∞) compared to [Ni(2)(dta)(4)I](∞), which features a rather large energy gap between the occupied and empty bands, and charge polarized dimer units. A larger electrical conductivity for the Pt chain can be expected, especially because the Fermi level lies within a band with contributions from Pt and I orbitals. Electronic structure parameters extracted from ab initio cluster calculations show that the large difference between the observed conductivities at 300 K for Ni and Pt compounds, of 3 orders of magnitude, cannot be explained from the parameters extracted from an embedded M(2)(dta)(4)I(2) dimer fragment alone. When tetramer fragments are considered, we observe that the interdimer transfer integral (t) between neighboring M(2) units connected by an iodine atom at correlated level is comparable in both chains. On the other hand, the energy to transfer an electron from a dimer to the neighboring one (Coulomb repulsion U) is three times larger in the Ni compound with respect to the Pt chain, in line with the poor conductivity of the former. The electronic structure of the M(4)(dta)(8)I(3) fragment points to an alternate charge-polarization state for Ni and an average valence state for Pt when the r.t. X-ray structure is considered.

Magnetic Coupling Constants of Self‐Assembled CuII [3×3] Grids: Alternative Spin Model from Theoretical Calculations

“…Most of the examples based on this strategy make use of the broken symmetry density functional theory (DFT) solutions [28][29][30][31][32][33][34][35][36][37] to evaluate the energy of the pertinent magnetic states. Also it is possible to find examples by using wavefunction-based approaches such as CASSCF/CASPT2 or difference-dedicated configuration interaction (DDCI) methods, [38][39][40][41][42] although in general they are less common than the applications on binuclear magnetic compounds, essentially due to their high computational cost. Regardless of the method employed to evaluate the energy of the magnetic states, the main constraint of the one-to-one mapping is the fact that the relevancy of the so-extracted parameters is linked to the validity of the a-priori-assumed spin model.…”

Multireference equation of motion coupled cluster benchmark study of magnetic model systems

“…A convenient approach to the problem is the construction of a model magnetic Hamiltonian [3,4], and the extraction of the parameters that enter the Hamiltonian from first principle quantum chemistry approaches (e.g., see refs. [5,6]). These approaches are well established, and have been reviewed, for example, Email address: nooijen@uwaterloo.ca (Marcel Nooijen) 1 Corresponding author in refs.…”

Electric Field Effects on Magnetic and Polarizability Properties of Clusters with Two-Electron Transfer

“…Such type of configurations in which the number of electrons in the atoms making up the systems differs by two have been detected in quasi-one-dimensional chains of palladium and platinum (e.g., Pd­(II)–Pd­(IV), Pt­(II)–Pt­(IV)), − three-dimensional networks and crystals of aurum (e.g., Au­(I)–Au­(III)) and antimony (e.g., Sb­(III)–Sb­(V) ,, ), as well as in binuclear clusters of Au­(I)–Au­(III), Ru(0)–Ru­(II), Pt­(II)–Pt­(IV), etc. A lot of experimental and theoretical work has been done for the explanation of the wide variety of the observed spectroscopic and magnetic properties of quasi-one-dimensional chains and three-dimensional networks and crystals with two-electron disproportionation demonstrating mixed valence, since their first appearance at the beginning of the twentieth century. − However, the possibility to manipulate the magnetic and spectroscopic characteristics of these systems with the aid of the external constant electric field has not been explored yet. The aim of the present paper is to examine the electric field effects in the magnetic and polarizabilty characteristics of isolated mixed-valence clusters with bielectronic transfer.…”