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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Two Distinct Cu(II)-V(IV) Superexchange Interactions with Similar Bond Angles in a Triangular ?CuV2? Fragment

The strength and sign of superexchange interactions are often predicted on the basis of the bond angles between magnetic ions, but complications may arise in situations with a nontrivial arrangement of the magnetic orbitals. We report on a novel molecular tetramer compound [Cu(H2O)dmbpy]2[V2O2F8] (dmbpy = 4,4 '-dimethyl-2,2 ' bipyridyl) that is composed of triangular "CuV2" fragments and displays a spin gap behavior. By combining first-principles calculations and electronic models, we reveal that superexchange Cu-V interactions carry drastically diHerent coupling strengths along two Cu-F-V pathways with comparable bond angles in the triangular "CuV2" fragment. Counterintuitively, their strong disparity is found to originate from the restricted symmetry of the half-filled Cu dx2-y2 orbital stabilized by the crystal field, leading to one dominating antiferromagnetic Cu-V coupling in each fragment. We revisit the magnetic properties of the reported spin-gapped chain compound [enH2]Cu(H2O)2[V2O2F8] (enH2 = ethylene diammonium) containing similar triangular "CuV2" fragments, and the magnetic behavior of the molecular tetramer and the chain compounds is rationalized as that of weakly coupled spin dimers and spin trimers, respectively. This work demonstrates that fundamentally diHerent magnetic couplings can be observed between magnetic ions with similar bond angles in a single spin motif, thus providing a strategy to introduce various exchange interactions combined with low dimensionality in heterometallic Cu(II)-V(IV) compounds.

Complexes↗
DOE OSTI2020

Materials Data on V3Cu by Materials Project

V3Cu is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. there are two inequivalent V sites. In the first V site, V is bonded in a distorted body-centered cubic geometry to four equivalent V and four equivalent Cu atoms. All V–V bond lengths are 2.57 Å. All V–Cu bond lengths are 2.57 Å. In the second V site, V is bonded in a 8-coordinate geometry to eight equivalent V and six equivalent Cu atoms. All V–Cu bond lengths are 2.96 Å. Cu is bonded in a distorted body-centered cubic geometry to fourteen V atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on V3Cu by Materials Project

V3Cu is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent V sites. In the first V site, V is bonded to eight V and four equivalent Cu atoms to form VV8Cu4 cuboctahedra that share corners with twelve equivalent VV8Cu4 cuboctahedra, edges with eight equivalent CuV12 cuboctahedra, edges with sixteen VV8Cu4 cuboctahedra, faces with four equivalent CuV12 cuboctahedra, and faces with fourteen VV8Cu4 cuboctahedra. There are four shorter (2.61 Å) and four longer (2.68 Å) V–V bond lengths. All V–Cu bond lengths are 2.68 Å. In the second V site, V is bonded to eight equivalent V and four equivalent Cu atoms to form distorted VV8Cu4 cuboctahedra that share corners with four equivalent VV8Cu4 cuboctahedra, corners with eight equivalent CuV12 cuboctahedra, edges with twenty-four VV8Cu4 cuboctahedra, faces with six equivalent CuV12 cuboctahedra, and faces with twelve VV8Cu4 cuboctahedra. All V–Cu bond lengths are 2.61 Å. Cu is bonded to twelve V atoms to form CuV12 cuboctahedra that share corners with four equivalent CuV12 cuboctahedra, corners with eight equivalent VV8Cu4 cuboctahedra, edges with eight equivalent CuV12 cuboctahedra, edges with sixteen equivalent VV8Cu4 cuboctahedra, faces with four equivalent CuV12 cuboctahedra, and faces with fourteen VV8Cu4 cuboctahedra.

36 MATERIALS SCIENCE↗