Microscopic Model for Photoinduced Magnetism in the Molecular Complex $[Mo(IV)(CN)_2(CN-CuL)_6]^{8+}$ Perchlorate

TL;DR

This paper develops an exact many-body theoretical model to explain the photoinduced magnetism observed in a specific heptanuclear molybdenum-copper complex, highlighting the role of excited charge-transfer states and their degeneracies.

Contribution

The paper introduces a novel valence bond approach to exactly solve a complex many-body model for photomagnetism in a specific molecular complex.

Findings

Optically excited charge-transfer states occur at ~3 eV across spin sectors.

Maximum degeneracy and transition dipole moment are in the S=3 spin sector.

The model explains the observed photomagnetism through excited state lifetimes and degeneracies.

Abstract

A theoretical model for understanding photomagnetism in the heptanuclear complex $[Mo(IV)(CN)_2(CN-CuL)_6]^{8+}$ perchlorate is developed. It is a many-body model involving the active orbitals on the transition metal ions. The model is exactly solved using a valence bond approach. The ground state solution of the model is highly degenerate and is spanned by five S=0 states, nine S=1 states, five S=2 states and one S=3 state. The orbital occupancies in all these states correspond to six $Cu(II)$ ions and one diamagnetic $Mo(IV)$ ion. The optically excited charge-transfer (CT) state in each spin sector occur at nearly the same excitation energy of 2.993 eV for the physically reasonable parameter values. The degeneracy of the CT states is largest in the S=3 sector and so is the transition dipole moment from the ground state to these excited states. Thus laser irradiation with light of this energy results in most intense absorption in the S=3 sector. The life-time of the S=3 excited states is also expected to be the largest as the number of states below that energy is very sparse in this spin sector when compared to other spin sectors. These twin features of our model explain the observed photomagnetism in the $[Mo(IV)(CN)_2(CN-CuL)_6]^{8+}$ complex.