# Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides

## Abstract

**:**

## 1. Introduction

## 2. Crystal Structures of Layered, Binary, Transition Metal Halides

#### 2.1. MX${}_{2}$ Compounds

#### 2.2. MX${}_{3}$ Compounds

## 3. Magnetic Structures of Layered, Binary, Transition Metal Halides

#### 3.1. MX${}_{2}$ Compounds

#### 3.1.1. TiX${}_{2}$ and ZrX${}_{2}$

#### 3.1.2. VX${}_{2}$

#### 3.1.3. MnX${}_{2}$

#### 3.1.4. FeX${}_{2}$

#### 3.1.5. CoX${}_{2}$

#### 3.1.6. NiX${}_{2}$

#### 3.2. MX${}_{3}$ Compounds

#### 3.2.1. VX${}_{3}$

#### 3.2.2. CrX${}_{3}$

#### 3.2.3. FeX${}_{3}$

#### 3.2.4. RuX${}_{3}$

## 4. Summary and Conclusions

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**A section of the periodic table showing the transition metals for which layered $M{X}_{2}$ compounds listed in Table 1 form. The metals are highlighted with colors that correspond to the structure types shown on the lower right. A plan view of a single layer common to both the CdI${}_{2}$ and CdCl${}_{2}$ structure types is shown on the upper right.

**Figure 2.**Crystal structures of layered Zr${X}_{2}$ compounds. A single Zr coordination polyhedron is shown for each structure.

**Figure 3.**A section of the periodic table showing the transition metals for which layered $M{X}_{3}$ compounds listed in Table 2 form. The metals are highlighted with colors that correspond to the structure types shown on the lower right. Crosshatching indicates multiple structures have been reported (see Table 2). A plan view of a single layer common to both the BiI${}_{3}$ and AlCl${}_{3}$ structure types is shown on the upper right, with coordinate systems corresponding to each structure type.

**Figure 4.**The 120${}^{\circ}$ magnetic structure determined for VCl${}_{2}$ and VBr${}_{2}$. The image shows a single triangular net of V atoms lying in the ab plane. Moments on the grey atoms are along the c axis. Moments on the black and blue atoms lie in the ac plane and are rotated by an angle of ±120${}^{\circ}$ from the c axis.

**Figure 5.**The lowest temperature, commensurate magnetic structure of MnBr${}_{2}$. The coordinate system refers to the underlying hexagonal crystal structure. Dark blue is used for Mn atoms with moments along the hexagonal a direction, and light blue for those with moments along -a.

**Figure 6.**The magnetic structures of Fe${X}_{2}$ with the hexagonal coordinate system of the underlying crystal lattice shown. All moments are along either the +c or -c direction.

**Figure 7.**Magnetic structures of Co${X}_{2}$ and Ni${X}_{2}$ for X = Cl and Br, and CoI${}_{2}$. The moments lie in the plane in each case, and are known to be parallel and antiparallel to the [210] direction in the commensurate structures of CoCl${}_{2}$ and Ni${X}_{2}$. A layer of the commensurate, cycloidal, helimagnetic structure of CoI${}_{2}$ reported in [41] is shown. A more complex cycloidal structure has also been reported [120]. Only a small portion of one layer of the lower temperature (T < 23 K) long period helimagnetic structure of NiBr${}_{2}$ is shown. Coordinate systems of the hexagonal crystallographic unit cells shown for reference.

**Figure 8.**Magnetic structures of Cr${X}_{3}$. The hexagonal coordinate system of the low temperature rhombohedral structure is shown. The moments in CrCl${}_{3}$ are drawn along the [110] and [$\overline{11}$0] directions here, but are only known to be in the ab plane. Moments are along the c axis in ferromagnetic CrBr${}_{3}$ and CrI${}_{3}$.

**Figure 9.**The helimagnetic structure of FeCl${}_{3}$. A portion of one layer of Fe atoms is shown, along with the hexagonal coordinate system. The dotted lines indicate (140) planes. The moment of the atoms lying on these planes is indicated by the red arrows at the left of each line. Moments are in the (140) planes and have components in and out of the page.

**Figure 10.**The zig-zag in plane magnetic structure of RuCl${}_{3}$. Coordinate systems corresponding to the underlying monoclinic and hexagonal crystal lattices are shown. The moments lie in the monoclinic ac plane, but the direction in this plane is not known well.

**Table 1.**Summary of structural and magnetic data for layered $M{X}_{2}$ compounds with partially filled d-shells. A * indicates that the compound is known to undergo a crystallographic phase transition above or below room temperature. “Magnetic order” refers to long range 3D magnetic order, and is given as antiferromagnetic (AFM), ferromagnetic (FM), or helimagnetic (HM). “Moments in layer” refers to the arrangement of the magnetic moments within a single layer, with $\left|\right|$ and ⊥ indicating whether the moments are directed parallel to the plane of the layer (in plane) or perpendicular to it (out of plane), respectively. Ordering temperatures (${T}_{N}$) and Weiss temperatures ($\theta $) are given. References for the magnetic data can be found in the associated text.

Compound | Structure Type | Reference | in Plane $\mathit{M}-\mathit{M}$ | Layer | Magnetic Order | Moments | ${\mathit{T}}_{\mathit{N}}$, (K) | $\mathit{\theta}$, (K) |
---|---|---|---|---|---|---|---|---|

Distance (Å) | Spacing (Å) | in Layer | ||||||

TiCl${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [44] | 3.56 | 5.88 | AFM | – | 85 | −702 |

TiBr${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [45] | 3.63 | 6.49 | – | – | – | – |

TiI${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [46] | 4.11 | 6.82 | – | – | – | – |

VCl${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [47] | 3.6 | 5.83 | AFM | 120${}^{\circ}$ | 36 | −565, −437 |

VBr${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [46] | 3.77 | 6.18 | AFM | 120${}^{\circ}$ | 30 | −335 |

VI${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [48] | 4.06 | 6.76 | AFM | – | 16.3, 15 | −143 |

MnCl${}_{2}$ | CdCl${}_{2}$ ($R\overline{3}m$) | [49] | 3.71 | 5.86 | AFM or HM | stripe or HM | 2.0, 1.8 | −3.3 |

MnBr${}_{2}$ * | CdI${}_{2}$ ($P\overline{3}m1$) | [50] | 3.89 | 6.27 | AFM | stripe $\left|\right|$ | 2.3, 2.16 | – |

MnI${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [51] | 4.16 | 6.82 | HM | HM | 3.95, 3.8, 3.45 | – |

FeCl${}_{2}$ | CdCl${}_{2}$ ($R\overline{3}m$) | [52] | 3.6 | 5.83 | AFM | FM ⊥ | 24 | 9 ($\left|\right|$), 21 (⊥) |

FeBr${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [53] | 3.78 | 6.23 | AFM | FM ⊥ | 14 | −3.0 ($\left|\right|$), 3.5 (⊥) |

FeI${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [54] | 4.03 | 6.75 | AFM | stripe ⊥ | 9 | 24 ($\left|\right|$), 21.5 (⊥) |

CoCl${}_{2}$ | CdCl${}_{2}$ ($R\overline{3}m$) | [55] | 3.54 | 5.81 | AFM | FM $\left|\right|$ | 25 | 38 |

CoBr${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [56] | 3.69 | 6.12 | AFM | FM $\left|\right|$ | 19 | – |

CoI${}_{2}$ | CdI${}_{2}$ ($P\overline{3}m1$) | [51] | 3.96 | 6.65 | HM | HM | 11 | – |

NiCl${}_{2}$ | CdCl${}_{2}$ ($R\overline{3}m$) | [57] | 3.48 | 5.8 | AFM | FM $\left|\right|$ | 52 | 68 |

NiBr${}_{2}$ | CdCl${}_{2}$ ($R\overline{3}m$) | [58] | 3.7 | 6.09 | AFM, HM | FM $\left|\right|$, HM | 52, 23 | – |

NiI${}_{2}$ * | CdCl${}_{2}$ ($R\overline{3}m$) | [59] | 3.9 | 6.54 | HM | HM | 75 | – |

ZrCl${}_{2}$ | MoS${}_{2}$ ($R3m$) | [60] | 3.38 | 6.45 | – | – | – | – |

ZrI${}_{2}$ | MoTe${}_{2}$ ($P{2}_{1}/m$) | [61] | 3.18, 3.74, 4.65 | 7.43 | – | – | – | – |

ZrI${}_{2}$ | WTe2 ($Pmn{2}_{1}$) | [62] | 3.19, 3.74, 4.65 | 7.44 |

**Table 2.**Summary of structural and magnetic data for layered $M{X}_{3}$ compounds with partially filled d-shells. A * indicates that the compound is known to undergo a crystallographic phase transition above or below room temperature. Multiple reported structure types are listed for some compounds. “Magnetic order” refers to long range 3D magnetic order, and is given as antiferromagnetic (AFM), ferromagnetic (FM), or helimagnetic (HM). “Moments in layer” refers to the arrangement of the magnetic moments within a single layer, with $\left|\right|$ and ⊥ indicating whether the moments are directed parallel to the plane of the layer (in plane) or perpendicular to it (out of plane), respectively, and “canted” indicating a canting away from either of these directions. Ordering temperatures (${T}_{N}$, ${T}_{C}$) and Weiss temperatures ($\theta $) are given. References for the magnetic data can be found in the associated text.

Compound | Structure Type | Reference | in Plane $\mathit{M}-\mathit{M}$ | Layer | Magnetic Order | Moments | ${\mathit{T}}_{\mathit{N}}$ or ${\mathit{T}}_{\mathit{C}}$, (K) | $\mathit{\theta}$, (K) |
---|---|---|---|---|---|---|---|---|

Distance (Å) | Spacing (Å) | in Layer | ||||||

TiCl${}_{3}$ * | BiI${}_{3}$ ($R\overline{3}$) | [28] | 3.53 | 5.83 | – | – | – | – |

TiCl${}_{3}$ * | Ti${}_{3}$O ($P\overline{3}1c$) | [70] | 3.55 | 5.86 | ||||

TiBr${}_{3}$ * | BiI${}_{3}$ ($R\overline{3}$) | [71] | 3.74 | 6.21 | – | – | – | – |

VCl${}_{3}$ | BiI${}_{3}$ ($R\overline{3}$) | [28] | 3.47 | 5.78 | AFM | – | ∼20 | −30 |

VBr${}_{3}$ | BiI${}_{3}$ ($R\overline{3}$) | [72] | 3.7 | 6.21 | – | – | – | – |

CrCl${}_{3}$ * | AlCl${}_{3}$ ($C2/m$) | [73] | 3.44, 3.44 | 5.80 | AFM | FM $\left|\right|$ | 15.5, 16.8 | 27 |

CrBr${}_{3}$ * | BiI${}_{3}$ ($R\overline{3}$) | [74] | 3.64 | 6.11 | FM | FM ⊥ | 37 | 47 |

CrI${}_{3}$ * | AlCl${}_{3}$ ($C2/m$) | [16] | 3.96, 3.97 | 6.62 | FM | FM ⊥ | 61 | 70 |

FeCl${}_{3}$ | BiI${}_{3}$ ($R\overline{3}$) | [75] | 3.50 | 5.80 | HM | HM | 9–10 | −11.5 |

FeCl${}_{3}$ | Ti${}_{3}$O ($P312$) | [76] | 3.50 | 5.80 | ||||

FeCl${}_{3}$ | FeCl${}_{3}$ ($P\overline{3}$) | [76] | 3.50 | 5.81 | ||||

FeBr${}_{3}$ | BiI${}_{3}$ ($R\overline{3}$) | [77] | 3.69 | 6.13 | AFM | – | 15.7 | – |

MoCl${}_{3}$ | AlCl${}_{3}$ ($C2/m$) | [78] | 2.76, 3.71 | 5.99 | – | – | – | – |

TcCl${}_{3}$ | AlCl${}_{3}$ ($C2/m$) | [79] | 2.86, 3.60 | 5.86 | – | – | – | – |

RuCl${}_{3}$ * | AlCl${}_{3}$ ($C2/m$) | [80] | 3.45, 3.45 | 5.69 | AFM | zig-zag canted | 7–8, 13–14 | 37 ($\left|\right|$), −150(⊥) |

RuCl${}_{3}$ * | Ti${}_{3}$O ($P312$) | [81] | 3.45 | 5.72 | ||||

RuCl${}_{3}$ * | CrCl${}_{3}$ ($P{3}_{1}12$) | [82] | 3.44, 3.45 | 5.73 | ||||

RhCl${}_{3}$ | AlCl${}_{3}$ ($C2/m$) | [83] | 3.44, 3.43 | 5.70 | – | – | – | – |

RhBr${}_{3}$ | AlCl${}_{3}$ ($C2/m$) | [84] | 3.62, 3.62 | 6.00 | – | – | – | – |

RhI${}_{3}$ | AlCl${}_{3}$ ($C2/m$) | [84] | 3.91, 3.90 | 6.45 | – | – | – | – |

IrCl${}_{3}$ | AlCl${}_{3}$ ($C2/m$) | [85] | 3.46, 3.45 | 5.64 | – | – | – | – |

IrBr${}_{3}$ | AlCl${}_{3}$ ($C2/m$) | [86] | 3.67, 3.64 | 6.01 | – | – | – | – |

IrI${}_{3}$ | AlCl${}_{3}$ ($C2/m$) | [86] | – | 6.54 | – | – | – | – |

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McGuire, M.A.
Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides. *Crystals* **2017**, *7*, 121.
https://doi.org/10.3390/cryst7050121

**AMA Style**

McGuire MA.
Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides. *Crystals*. 2017; 7(5):121.
https://doi.org/10.3390/cryst7050121

**Chicago/Turabian Style**

McGuire, Michael A.
2017. "Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides" *Crystals* 7, no. 5: 121.
https://doi.org/10.3390/cryst7050121