Two-Dimensional Multifunctional Metal–Organic Framework with Intrinsic Bipolar Magnetic Semiconductivity and Negative Poisson’s Ratio

Abstract

Two-dimensional (2D) materials with simultaneous magnetic semiconducting properties and negative Poisson's ratio are crucial for fabricating multifunctional electronic devices but remain limited. Herein, on the basis of first-principles calculations, we design the 2D metal−organic framework Cr(DCNQI) 2 (DCNQI = N,N′-dicyanoquinonediimine) as a notable candidate with good dynamic, thermal, and mechanical stabilities. Interestingly, 2D Cr(DCNQI) 2 harbors an unusual in-plane negative Poisson's ratio with a maximum absolute value of 0.85, which is fairly large and scarce in reported auxetic materials. Due to the strong d−p direct exchange magnetic interaction between Cr cations and DCNQI anions, 2D Cr(DCNQI) 2 exhibits intrinsic ferrimagnetism with a relatively high Curie temperature of 217 K. Also, it possesses significant out-of-plane magnetic anisotropy (0.60 meV/Cr). In addition, 2D Cr(DCNQI) 2 behaves as an intrinsic bipolar magnetic semiconductor with a moderate direct band gap of 0.95 eV and small carrier effective masses. Electrical doping induces the transformation of 2D Cr(DCNQI) 2 into a half-metal with controllable spin polarization.

Quintuple Function Integration in Two-Dimensional Cr(II) Five-Membered Heterocyclic Metal Organic Frameworks via Tuning Ligand Spin and Lattice Symmetry

“…The maximum value of NPR can reach about −0.12 in the 5% strain range. This value is smaller than that of 2D Cr(dicyanoquinonediimine) 2 (−0.85), but comparable to most reported 2D inorganic auxetic materials, such as Ag 2 S (−0.12), Be 5 C 2 (−0.16), and SnSe (−0.17) . The auxetic property endows 2D Cr(TDZ) 2 with potential applications in nanomechanics (such as auxetic strain-sensors and auxetic pumps) and defense and aerospace aspects.…”

“…17 By using dicyanoquinonediimine as a rotatory unit, the Cr(dicyanoquinonediimine) 2 sheet has been predicted to be an auxetic magnet. 10 By changing the spin state of organic linkers from singlet to doublet and introducing a strong d-p direct ferrimagnetic (FiM) exchange interaction, high Curie temperature (T C ) magnetic semiconductors (SCs) Cr(pentalene) 2 (T C = 560 K), 11 Cr(diketopyrrolopyrrole) 2 (T C = 316 K), 15 and Cr(pyrazine) 2 (T C = 342 K) 12,13 have been designed theoretically. Via distorting the out-of-plane K + counterions, ferroelectric 2D magnetic K 3 M 2 [PcMO 8 ] (M = Cr-Co) sheets have been forecasted.…”

“…Considering the structural rigidity and limited tunability of inorganic compounds, we turn our attention to organometallic materials with structural variability and rich functionalization possibilities. , Organometallic frameworks are hybrid porous materials composed of abundant metal nodes and inexpensive organic linkers . By tuning metal nodes or organic linkers or the connectivity between them, they can possess functional properties with potential applications in traditional fields of gas separation, sensing, and optoelectronics − or emerging fields of electromechanical, magnetoelectronic, and topological quantum technologies. − For instance, by selecting benzimidazole as an organic linker, ultrathin poly­[Zn 2 (benzimidazole) 4 ] sheets exhibit excellent performance in H 2 /CO 2 gas separation . By using dicyanoquinonediimine as a rotatory unit, the Cr­(dicyanoquinonediimine) 2 sheet has been predicted to be an auxetic magnet .…”

“…By tuning metal nodes or organic linkers or the connectivity between them, they can possess functional properties with potential applications in traditional fields of gas separation, sensing, and optoelectronics − or emerging fields of electromechanical, magnetoelectronic, and topological quantum technologies. − For instance, by selecting benzimidazole as an organic linker, ultrathin poly­[Zn 2 (benzimidazole) 4 ] sheets exhibit excellent performance in H 2 /CO 2 gas separation . By using dicyanoquinonediimine as a rotatory unit, the Cr­(dicyanoquinonediimine) 2 sheet has been predicted to be an auxetic magnet . By changing the spin state of organic linkers from singlet to doublet and introducing a strong d - p direct ferrimagnetic (FiM) exchange interaction, high Curie temperature ( T C ) magnetic semiconductors (SCs) Cr­(pentalene) 2 ( T C = 560 K), Cr­(diketopyrrolopyrrole) 2 ( T C = 316 K), and Cr­(pyrazine) 2 ( T C = 342 K) , have been designed theoretically.…”

“…Among numerous organometallic frameworks, a transition metal Cr atom as a common metal node has been widely used, − and its related planar tetracoordinate molecules or crystals have been extensively synthesized. − Although divalent Cr compounds are uncommon in chemistry, Perlepe et al have prepared a layered Li 0.7 [Cr­(pyrazine) 2 ]­Cl 0.7 ·0.25­(THF) (THF = tetrahydrofuran) crystal with room-temperature ferrimagnetism under a dinitrogen or argon atmosphere in which each Cr­(II) is coordinated to four pyrazine organic linkers within the layers forming a square planar lattice . If the pyrazine rings are replaced by inversion symmetry-breaking organic linkers, the functional properties can be further enriched as extra tunable degrees of freedom are introduced into the crystal structure.…”