Geometric Structures and Magnetic Interactions in Small Chromium Oxide Clusters

Abstract

The physical and chemical properties of transition metal oxide particles result from the subtle interplay between atomic ordering and electronic structure, the latter being determined by a complex interaction between the partially filled d subshell of the transition metal atoms and the oxygen 2p orbitals. In this article, the geometric ground state structures of several experimentally synthesized cationic chromium oxide clusters Cr m O + n (m = 2, 3, 4; n ≤ m) are characterized through infrared photodissociation spectroscopy on cluster-rare gas atom complexes in combination with quantum chemical calculations. Computational analysis of the electronic and magnetic properties of the identified isomers demonstrated that the magnetic configuration of the clusters varies with the size and oxidation state. Superexchange interaction causes ferromagnetic coupling in Cr 2 O + 2 and Cr 3 O + 3 , while 3d-3d bonding-like interaction between two chromium atoms underlies ferrimagnetic behavior in Cr 3 O + , Cr 3 O + 2 , and Cr 4 O + 4. The highest possible total magnetic moments are obtained in suboxides that have Cr−O−Cr bridges with a unique oxygen atom between each pair of Cr atoms. The addition of more oxygen atoms enhances the delocalization of the Cr 3d electrons and reduces the magnetic moment.

Structures and Magnetism of Cationic Chromium–Manganese Bimetallic Oxide Clusters

“…Total magnetic moments of both series decrease under addition of oxygen atoms (see Figure a). In CrMnO 2 + , superexchange interaction through bridging oxygen facilitates the maximum total magnetic moment as observed in Cr 2 O 2 –/0/+ . ,, The total magnetic moment of CrMnO z + decreases under addition of oxygen atoms owing to capture of metal electrons in metal–O bonds . For clusters containing three metal atoms, no systematic trend is observed.…”

“…Quantum chemical calculations were done with the Gaussian 09 program, and London-dispersion corrections were taken into account using the DFT-D3 parameters for the supported functionals (TPSS and BP86). The DFT-D3 version from 2010 (with zero-damping) was chosen due to its previously reported good performance for similar clusters . Note that London-dispersion corrections can be influential in the determination of geometries; for a recent review, see ref .…”

“…The electronic ground states of the neutral Cr 2 and Mn 2 dimers are singlets due to antiferromagnetic coupling between the local spin magnetic moments on the atoms. − However, the ground states of the cationic dimers possess high-spin magnetic moments (11 μ B ) as a result of ferromagnetic coupling. − Considering the bimetallic CrMn dimer, the local magnetic moments are ferrimagnetically coupled, leading to a small net magnetic moment of 3 μ B . , In larger clusters, the magnetic behavior of chromium and manganese gradually diverge. Cr 3 was found to have a quartet ground state as a result of ferrimagnetic coupling, while Mn 3 ferrimagnetic and ferromagnetic states were found to be energetically competitive. − An energetic competition between two ferrimagnetic states (S = 1 vs S = 6) was predicted for Cr 4 , while for Mn 4 , the ferromagnetic state is clearly preferred. , In bulk materials, chromium is antiferromagnetic at room temperature, while the stable α phase of manganese is paramagnetic . Above 311 K, bulk chromium is paramagnetic as well …”

Infrared Photodissociation Spectroscopy of Heteronuclear Arsenic–Iron Carbonyl Cluster Anions

“…Natural bond orbital (NBO) analysis was performed to study the atomic electronic charge distributions and bonding character of the cluster anions. The hybrid functional B3LYP, pure functional BP86, and meta -GGA functional TPSS are among the most popular density functionals and have proven to provide reliable predictions on the structures and vibrational frequencies of arsenic clusters and transition-metal-containing clusters. ,− Throughout the calculation process, the three functionals agreed well in their isomer location predictions. To be consistent with our previous studies, − the optimized structures and the frequencies obtained using the B3LYP functional were used unless stated otherwise.…”

Increased Excited State Metallicity in Neutral Cr2On Clusters (n < 5) Upon Sequential Oxidation

“…[14][15][16] The electronic structures of Cr2On clusters arise from a unique mixing of Cr half-filled s-and d-orbitals (3d 5 4s 1 ) with O 2p-orbitals. The properties of chromium oxides are driven partially by superexchange coupling, 8,17 suggesting the chargetransport processes are adiabatic in nature. Manipulation of spin in antiferromagnetic (AF) Cr2O3 bulk materials follows several relaxation channels dependent on excitation energy, proceeding over hundreds of femtoseconds to picoseconds.…”