Structural, Electronic, and Magnetic Properties of Neutral Borometallic Molecular Wheel Clusters

Abstract

Atomic clusters exhibit properties that fall between those found for individual atoms and bulk solids. Small boron clusters exhibit planar and quasiplanar structures, which are novel materials envisioned to serve as a platform for designing nanodevices and materials with unique physical and chemical properties. Through past research advancements, experimentalists demonstrated the successful incorporation of transition metals within planar boron rings. In our study, we used first-principles calculations to examine the structure and properties of neutral boron clusters doped with transition metals, denoted as TMB_n and TMB_2n, where TM = Ti, Cr, Mn, Fe, Co, Nb, or Mo and $n=8–10$. Our calculations show that the TMB_2n structures, which involve sandwiching metal atoms between two rings (called the drum configuration), and clusters with the single ring configuration, TMB_n, are stable. These clusters typically have relatively large HOMO-LUMO energy gaps, suggesting high kinetic stability and low chemical reactivity. Moreover, the clusters display interesting magnetic properties, determined not only by the metal atoms but also by the induced magnetism of the boron rings. These structures have potential applications in spintronics and sensing. This work also provides a basis for studying magnetism in the one-dimensional limit.

1. Introduction

Boron, a versatile element with applications spanning many fields, has a rich history that traces its origins to the isolation of simple boranes by Stock et al. [1]. Over the past two decades, a noteworthy chapter in this narrative has unfolded with the synthesis and characterization of various low-dimensional boron nanomaterials, including nanoclusters, nanowires, nanotubes, nanobelts, nanoribbons, and monolayer crystalline sheets [2,3,4,5]. Unlike traditional bulk boron crystals found in $\alpha$-, $\beta$-, and $\gamma$-rhombohedral and $\alpha$-tetragonal forms, these newly crafted boron-based nanomaterials have distinctive bonding patterns [6]. This departure gives rise to captivating physical and chemical properties, making them a focal point of fascination within materials science. Of particular note is the capability of boron-based nanomaterials, such as clusters, to serve as superatoms or as fundamental building blocks for crafting nanostructures designed with novel functionalities and properties. These systems are characterized by having diverse structures, including planar, quasiplanar, bowl, cage, tubular drum-like forms, multiple ring tubes, and fullerenes [7,8,9,10,11]. Electron deficiency of the boron atom enables its involvement in localized and delocalized bonding patterns across various geometric configurations. The neutral B_n clusters with $n<20$ prefer a planar or quasiplanar structure [12]. On the other hand, ${\mathrm{B}}_n^{-}$ clusters retain planarity (or quasiplanarity) for $n\le 40$ [13]. The perfectly planar B₈ and ${\mathrm{B}}_9^{-}$ molecular wheels, with a hepta- or octacoordinated central boron atom, respectively, laid the foundation of borometallic clusters [14]. In the borometallic cluster, the central B atom is replaced by a metal atom, creating a similar doubly aromatic cluster [15,16]. Experiments in cluster beams have demonstrated that transition metal (TM) atoms can be incorporated into the center of the planar boron clusters [17,18,19].

In a more recent study by Zhang et al. [20], the CALYPSO structure search method was used to investigate the global minimum structures of neutral and negatively charged Ta₂B_n clusters, where n ranges from 1 to 10. Their findings revealed the formation of a B ring when n equals 6. Interestingly, the research identified a neutral Ta₂B₆ cluster exhibiting a bipyramidal configuration with enhanced stability. Chang Xu et al. [21] conducted a theoretical investigation on TM-centered double-ring clusters, M@B_2n (where M = Ti, Cr, Fe, Ni, Zn and n = 6, 7, 8). They explored the factors contributing to the stability of these clusters in their study. Miao Yan et al. [22] introduced the concept of fluxional bonds in various structures, including planar ${\mathrm{B}}_{19}^{-}$, tubular Ta@${\mathrm{B}}_{20}^{-}$, and cage-like ${\mathrm{B}}_{39}^{-}$. These bonds form and break continuously on these systems’ extremely flat potential energy surfaces. Ren et al. [23] used the CALYPSO method combined with density functional theory (DFT) calculations on niobium-doped boron clusters. Their research revealed that the global minima for the neutral clusters correspond to half-sandwich structures at $n=10–17$ and tubular-type structures at $n=18–20$. Chen et al.’s [24] study offered a comprehensive overview of the geometric configurations of both pure (B_n) and metal-doped boron clusters, which exhibit structures such as planar, nanotube, bilayer, fullerene-like, and core-shell forms across a wide range of cluster sizes (n). They also explored the potential for developing boron-based nanomaterials with specific functionalities derived from metal–boron clusters. Liu et al. [25] identified ten potential clusters made up of rings formed by 12 to 15 atoms of boron–carbon doped with heavier alkaline-earth (Ae) metals (Ae = Ca, Sr, Ba). Their chemical bond analysis reveals the important role of Ae d orbitals in facilitating covalent interactions between the central Ae atom and the surrounding boron–carbon rings.

Linear magnetic chains are becoming crucial in quantum information involving entanglement and correlation [26,27]. Carbon and boron-nitride-based nanotubes are used as support surfaces to stabilize unstable isolated atomic chains [28]. Photoelectron spectroscopy and theoretical studies identified metal-centered tubular ionic structures ${\mathrm{MnB}}_{16}^{-}$, ${\mathrm{CoB}}_{16}^{-}$, ${\mathrm{RhB}}_{18}^{-}$, and ${\mathrm{TaB}}_{20}^{-}$ with a magnetic moment of 2, 2, 0, and 0 $\mu \mathrm{B}$, respectively [29,30,31,32]. Neutral boron-based tubular structures, including FeB₁₄, FeB₁₆, UB₂₀, NpB₂₀, and PuB₂₀, were theoretically examined and found to have a quenched magnetic moment of 2 $\mu \mathrm{B}$ for the iron-based structures and relatively high magnetic moment of 3.69, 4.92, and 6.07 $\mu \mathrm{B}$, respectively, for actinide-centered tubular structures [33,34]. These research works showed that the size and stability of the tubular structures greatly depend on the encapsulated metal atoms through the covalent bonds forming between the metal ions and the boron frame (MB_n) [35]. Metal-centered tubular boron clusters have been suggested as the building blocks for one-dimensional metallo-nanotubes [35]. However, the magnetic moments of TM-centered tubular boron clusters remain unexplored, with limited discussion on their magnetic behaviors.

In this work, using DFT calculations, we study the structure and properties of molecular borometallic wheel structures derived from planar boron B₈, B₉, and B₁₀ wheel clusters. For all of these clusters, we analyze their magnetic behavior using spin-polarized calculations and analyze charge density differences and the contribution of metal and boron atoms to the density of states via the projected density of states (PDOS) analysis.

2. Computational Details

In our DFT-based study, we use the plane-wave-based Quantum ESPRESSO package [36]. The generalized gradient approximation (GGA) of Perdew–Burke–Ernzerhof (PBE) [37] is employed in the calculations combined with projector-augmented wave (PAW) pseudopotentials. Boron-based rings centered with TM atoms (TMB_n) are modeled by varying the value of n from 8 to 10 for single rings and subsequently increasing it to 16, 18, and 20 by taking the same ring twice and sandwiching the metal atom between them (TMB_2n). The TMB_n and TMB_2n clusters are shown in Figure 1. A vacuum distance of 16 Å is introduced to avoid interactions between cluster replicas. A plane-wave basis set with an energy cutoff of 70 Ry is used. The convergence threshold for the self-consistent energy calculations is ${10}^{-12}$, and the atomic positions are optimized until the forces on atoms are smaller than ${10}^{-4}$ Ry/Bohr. The convergence threshold during phonon self-consistent calculations is ${10}^{-14}$ eV. All the computations are carried out at the $\mathsf{\Gamma }$-point of the Brillouin zone. Assessing the stability of clusters often relies on the binding energy, $E_b$, as an important parameter. The calculation of $E_b$ for the TMB_n and TMB_2n clusters is conducted using the following equation:

$$E_b=E\left({\mathrm{TMB}}_i\right)-E\left({\mathrm{B}}_i\right)-E\left(\mathrm{TM}\right),$$

where $E\left({\mathrm{TMB}}_i\right)$ is the total energy of the optimized boron ring with the TM atom in the center, $E\left({\mathrm{B}}_i\right)$ is the total energy of the boron cluster in the ring ($i=n$) or drum ($i=2n$) forms, and $E\left(\mathrm{TM}\right)$ is the energy of the isolated TM atom. Spin-polarized calculations are carried out to study the magnetic properties of the clusters.

3. Results and Discussion

We became interested in the high symmetry of aromatic boron B₈ and ${\mathrm{B}}_9^{-}$ clusters, which are perfect heptagon and octagon structures with D_7h and D_8h symmetries, respectively [38]. This led us to conduct thorough investigations involving neutral clusters formed by replacing the central B atom in the octagon boron structure with TM counterparts, specifically TM = Ti, Cr, Mn, Fe, Co, Nb, and Mo, and extending the study to larger borometallic clusters. Our investigation focused on two primary configurations: the above-mentioned “ring configuration” (TMB_n), featuring a TM atom at the center of a ring composed of 8, 9, or 10 boron atoms, and the “drum configuration” (TMB_2n), involving two rings of the same size stacked on top of each other, with the metal atom situated between the centers of two rings comprising 8, 9, or 10 boron atoms. Our system is visually represented in Figure 1, with boron atoms highlighted in dark red and forming a ring, and the central TM atom is shown in blue.

3.1. Structural Properties

In line with the structural arrangement shown in Figure 1, the bond lengths between adjacent boron atoms ($d_{\mathrm{B}-\mathrm{B}}$) and those connecting boron with central metal atoms ($d_{\mathrm{B}-\mathrm{TM}}$) are summarized for all the studied clusters in

Table 1. Calculated parameters related to each studied structure: bond length between boron atoms ($d_{\mathrm{B}-\mathrm{B}}$), bond length between boron and metal atoms ($d_{\mathrm{B}-\mathrm{TM}}$), point group (PG), magnetic moment (m), H-L energy gap, and binding energy ($E_b$).

${\mathbf{MB}}_{\mathit{n}}$	${\mathit{d}}_{\mathbf{B}-\mathbf{B}}$	${\mathit{d}}_{\mathbf{B}-\mathbf{TM}}$	PG	m	H-L Gap	${\mathit{E}}_{\mathit{b}}$
	(Å)	(Å)		(${\mathit{\mu }}_{\mathbf{B}}$)	(eV)	(eV)
TiB8	1.578	2.226	$C_s$	4	0.541	−9.667
TiB9	1.558	2.335	$C_s$	3	0.090	−10.692
TiB10	1.536	2.485	$D_{2h}$	2	0.617	−11.106
TiB16	1.639	2.275	$C_s$	0	0.392	−8.214
TiB18	1.608	2.460	$C_1$	2	0.246	−9.245
TiB20	1.579	2.593	$C_1$	2	0.312	−7.925
CrB8	1.587	2.073	$D_{4h}$	4	0.004	−11.476
CrB9	1.551	2.269	$C_s$	3	0.367	−12.495
CrB10	1.524	2.466	$C_{2h}$	2	0.357	−12.152
CrB16	1.614	2.209	$C_{2v}$	0	0.822	−11.234
CrB18	1.588	2.432	$C_1$	1.8	0.122	−10.471
CrB20	1.608	2.645	$C_1$	4	0.425	−8.272
MnB8	1.572	2.054	$D_{4h}$	3	0.486	−7.288
MnB9	1.542	2.255	$C_{2v}$	2	0.880	−7.733
MnB10	1.530	2.473	$C_{2h}$	3	0.264	−7.128
MnB16	1.602	2.235	$C_{2v}$	1	0.804	−6.472
MnB18	1.584	2.431	$C_1$	1	0.558	−5.397
MnB20	1.602	2.723	$C_1$	3	0.439	−3.518
FeB8	1.564	2.065	$C_{4v}$	2	0.016	−10.866
FeB9	1.533	2.241	$C_{2v}$	1	0.785	−12.050
FeB10	1.523	2.461	$C_{2h}$	2	0.274	−11.099
FeB16	1.594	2.231	$C_{4v}$	1.49	0.063	−9.955
FeB18	1.581	2.445	$C_1$	2	0.324	−8.645
FeB20	1.617	2.760	$C_1$	2	0.268	−7.918
CoB8	1.564	2.044	$D_{4h}$	1	0.001	−15.709
CoB9	1.539	2.234	$C_{2v}$	0	1.055	−15.889
CoB10	1.522	2.462	$D_{2h}$	3	0.404	−14.585
CoB16	1.591	2.232	$C_{4v}$	1	0.297	−13.398
CoB18	1.579	2.443	$C_s$	1	0.311	−11.828
CoB20	1.619	2.749	$C_1$	1	0.258	−11.881
NbB8	1.653	2.157	$D_{4h}$	3	0.504	−10.702
NbB9	1.573	2.300	$C_{2v}$	2	0.418	−13.055
NbB10	1.533	2.481	$D_{2h}$	1	0.907	−13.451
NbB16	1.661	2.306	$C_s$	1	0.322	−10.318
NbB18	1.561	2.477	$C_1$	1	0.362	−12.179
NbB20	1.573	2.674	$C_1$	0	0.000	−10.937
MoB8	1.628	2.126	$D_{4h}$	2	0.419	−12.395
MoB9	1.560	2.281	$C_{2v}$	2.44	0.080	−14.021
MoB10	1.524	2.467	$C_s$	0	0.092	−13.998
MoB16	1.658	2.249	$C_{2v}$	0	0.616	−11.811
MoB18	1.602	2.431	$C_1$	0	0.415	−12.663
MoB20	1.568	2.760	$C_1$	0	1.088	−10.871

. It is worth noting that all the designed configurations are planar except for TiB₈, TiB₉, and FeB₈ where the central atom deviates slightly out of plane by 0.8387 Å, 0.6168 Å, and 0.8394 Å, respectively, giving rise to a distinctive bowl-like structure, which aligns well with previous research. The distances between metal and boron atoms ($d_{\mathrm{B}-\mathrm{TM}}$) for $n=8$, 9, and 16 are small compared to their covalent bonds, indicating minimal steric repulsion between them. The bond length $d_{\mathrm{B}-\mathrm{B}}$ is influenced by the number of B atoms present in the boron ring and the size of the central metal atom, especially for $n=8$ and 9 (refer to Table 1). For TM = Cr, Mn, Fe, or Co, the drum configuration with the maximum number of boron atoms is only possible with B₁₈ because, beyond that limit, an elliptical geometry prevails over a circular shape. In Table 1, we summarize the point group (PG) symmetry for each cluster, which was determined using the AFLOW software [39]. Except for the non-planar structures, the $D_{4h}$ symmetry is assigned to TMB₈. For TMB₁₀ clusters, the PG symmetry is $D_{2h}$ due to its nearly circular geometry or $C_{2h}$ due to its elliptical geometry. Similar trends have been reported for ${\mathrm{TaB}}_n^{-}$ clusters [40]: ${\mathrm{TaB}}_8^{-}$ forms a pyramidal structure, ${\mathrm{TaB}}_9^{-}$ shows increased planarity as the Ta atom integrates into a larger boron ring, and ${\mathrm{TaB}}_{10}^{-}$ achieves a perfectly planar, decacoordinated $D_{10h}$ symmetry, representing the highest coordination for Ta in planar geometry, stabilized by aromaticity. Drum configurations mostly belong to the $C_1$ PG symmetry.

In Table 1, we have summarized the values of $E_b$ for all the clusters. The $E_b$ values consistently increase from TMB₈ to TMB₉ (or, in some cases, TMB₈ to TMB₁₀) and then decrease gradually until reaching TMB₂₀ across all seven systems for each TM. Overall, the $E_b$ values are relatively high for Co-doped configurations but notably lower for Mn-doped structures. It is important to note that all structures have negative $E_b$ values, indicating the stability of the clusters since energy is required to separate them into TM and B_n.

3.2. Electronic Properties

In Table 1, we have summarized the HOMO-LUMO (H-L) energy gaps of the studied clusters. Although DFT-GGA underestimates energy gap values, most clusters still exhibit nonzero H-L energy gaps. The largest energy gaps for the ring configurations are found in CoB₉, NbB₁₀, and FeB₉, with values of 1.055 eV, 0.907 eV, and 0.785 eV, respectively. Among the drum configurations, the H-L energy gaps for MoB₂₀, CrB₁₆, and MnB₁₆ (1.088 eV, 0.822 eV, and 0.804 eV, respectively) are larger compared to other drum structures. It is well established that DFT-based approaches systematically underestimate energy gaps [41]. Therefore, the true H-L energy gaps of the clusters may be even twice larger. Structures with large H-L energy gaps are associated with high kinetic stability and low chemical reactivity, making them promising candidates for future applications.

The PDOS spectra for all the clusters can be found in Section SI of the Supplementary Materials (SM). These spectra are valuable for studying the contribution of different atomic orbitals to the density of states in the studied clusters, particularly at and near the Fermi level, $E_{\mathrm{F}}$. They also aid in visualizing the contribution of atomic orbitals to the magnetic properties of the clusters (e.g., to the shift between the spin-up and spin-down PDOS). In general, the p-orbitals of boron and the d-orbitals of TMs make the most significant contributions to the density of states at the $E_{\mathrm{F}}$. However, in specific cases such as TiB₉, FeB₈, CoB₈, and NbB₂₀, the contribution at the $E_{\mathrm{F}}$ comes solely from boron p-orbitals. A combination of boron p and TM d orbitals contribute to the density of states at the $E_{\mathrm{F}}$ for CrB₈, CrB₁₈, FeB₁₆, MoB₉, and MoB₁₀.

Cluster-specific observations, as inferred from the PDOS spectra, show distinct contributions to the highest occupied states, which can be summarized as follows: In the Ti series, B p-orbitals dominate in TiB₉, TiB₁₀, and TiB₂₀. In contrast, a mix of B p and TM d occurs in TiB₈, TiB₁₆, and TiB₁₈. In the Cr series, B p-orbitals significantly contribute in CrB₉ and CrB₁₆, and a mix of B p and TM d contributions occur in the rest of the Cr-based clusters. In the Mn and Fe series, the clusters frequently exhibit combined B p and TM d contributions with a consistent magnetic character. For Co-based clusters, the electronic configurations reveal that boron p-orbitals dominate the highest occupied states in CoB₈, CoB₁₆, CoB₁₈, and CoB₂₀, all of which are magnetic except for CoB₈, which lacks an H-L energy gap. In contrast, CoB₉ and CoB₁₀ exhibit contributions from both boron p- and TM d-orbitals to the highest occupied states, with CoB₉ being nonmagnetic and CoB₁₀ magnetic. Similarly, in Nb-based clusters, boron p-orbitals primarily contribute to the highest occupied states in NbB₈, NbB₁₆, and NbB₁₈, which are magnetic with H-L energy gaps, and NbB₂₀, which is nonmagnetic without an H-L energy gap. Clusters NbB₉ and NbB₁₀ exhibit combined contributions from boron p- and TM d-orbitals, maintaining magnetic properties and distinct H-L energy gaps. Finally, in the Mo series, most of the structures are nonmagnetic (e.g., MoB₁₈ and MoB₂₀), which is reflected in the symmetry of the spin-up and spin-down PDOS, contrasting with the magnetic nature of smaller clusters like MoB₉.

These observations highlight the nuanced role of TM d-orbitals and B p-orbitals in shaping the electronic and magnetic characteristics of borometallic clusters. The variability in orbital contributions underscores the tunable properties of these materials.

3.3. Vibrational Properties

The vibrational properties of the structures were analyzed using phonon computations to assess their stability. These calculations provide valuable insights into the dynamic behavior and structural integrity of the systems under study. According to the literature [42], a cluster is considered stable if all its real vibrational frequencies are positive and the minimum vibrational frequency, denoted as $f_{min}$, is significantly large.

Table 2. Minimum vibrational frequencies for each studied cluster.

Ring	${\mathit{f}}_{\mathit{min}}$ (cm−1)	Drum	${\mathit{f}}_{\mathit{min}}$ (cm−1)
TiB8	206.22	TiB16	48.41
TiB9	123.91	TiB18	65.62
TiB10	85.00	TiB20	78.17
CrB8	87.93	CrB16	160.53
CrB9	196.47	CrB18	59.27
CrB10	44.03	CrB20	89.9
MnB8	140.21	MnB16	122.13
MnB9	135.68	MnB18	130.70
MnB10	69.60	MnB20	27.00
FeB8	133.40	FeB16	75.14
FeB9	128.48	FeB18	79.27
FeB10	−22.1	FeB20	64.30
CoB8	132.22	CoB16	55.24
CoB9	102.07	CoB18	70.30
CoB10	78.0	CoB20	90.34
NbB8	45.69	NbB16	153.38
NbB9	93.35	NbB18	38.60
NbB10	87.85	NbB20	102.61
MoB8	29.26	MoB16	86.96
MoB9	95.29	MoB18	41.17
MoB10	68.08	MoB20	106.48

presents the values of $f_{min}$ for each cluster. For the ring configuration, TMB₈ and TMB₉ with TM = Ti, Cr, Mn, Fe, or Co have the highest values of $f_{min}$, whereas TMB₉ and TMB₁₀ clusters have the highest $f_{min}$ for TM = Nb and Mo. Interestingly, the FeB₁₀ cluster in our calculations is at the border of stability as its $f_{min}$ value is small but negative. For the drum configurations, there is less regularity, and large values of $f_{min}$ are obtained for CrB₁₆, while the lowest value is for MnB₂₀. Our results for $f_{min}$ are in close agreement with a study by Pu et al. [19], where the values of $f_{min}$ for FeB₉ and CoB₉ were 110.5 cm⁻¹ and 96.7 cm⁻¹, respectively. The complete list of phonon frequencies for each cluster is provided in Section SII of SM.

3.4. Dynamic Properties

To further verify the stability of the ring and drum structures, we performed quantum molecular dynamics (MD) simulations at two different temperatures with the choice of 1 fs for the time step. Each run was 3.5 ps long. At a temperature of 300 K, the ring and drum structures maintain their shape during the MD run, and no significant deformations occur. Both structure types deform at a temperature of 600 K but retain their wheel-like structure. This is shown in Figure 2 on the example of CoB₉ and MnB₁₈. It is worth noting that MnB₁₈ has one of the smallest $E_b$ in absolute value.

3.5. Magnetic Properties

The magnetic moment values, denoted as m, for each cluster, are listed in Table 1. Generally, the value of m decreases as the number of boron atoms in the ring increases from 8 to 10. In contrast, an opposite trend is observed for drum structures, with m tending to increase as the number of boron atoms in the TMB_n structure increases (from 16 to 20). Interestingly, the m values for CoB_n and MoB_n drum structures are independent of n, remaining equal to 1 $\mu \mathrm{B}$ and 0 $\mu \mathrm{B}$, respectively.

The contribution from boron and TM atoms to magnetization is illustrated in Figure 3. In general, the contribution from TM atoms to total m is large. However, in most cases, the boron atoms become polarized, resulting in a non-zero contribution to m. Specifically, for TMB₈ clusters, the boron contribution (represented by the yellow line) to m is consistently larger than the TM contribution (represented by the blue line). Conversely, metals demonstrate dominance in the case of TMB₁₀ structures. For drum configurations, both metal and boron atoms consistently exhibit positive (or zero) contributions to m, except for the case of Mn, where boron atoms have slightly negative local magnetization. The case of NbB_n clusters is particularly interesting, as TM atoms induce the magnetization, but m is entirely localized on the boron atoms.

The result presented in Figure 3 can be spatially visualized by drawing the difference between the spin-up charge density (${\rho }^{\uparrow }$) and the spin-down charge density (${\rho }^{\downarrow }$):

$$\mathit{spin}\mathit{polarization}\mathit{density}={\rho }^{\uparrow }\left(\overrightarrow{r}\right)-{\rho }^{\downarrow }\left(\overrightarrow{r}\right).$$

This can be seen in Figure 4 where the positive and negative values of the spin polarization density are represented with yellow and cyan, respectively. This figure clearly shows that the boron atoms in all clusters become polarized, and this polarization significantly influences the total value of m. Our Löwdin population analysis provided in Section SIII of SM quantitatively demonstrates this. This analysis evidenced, in most cases, a charge transfer from/to the TM atom, which gives rise to polarization effects on the boron atoms that, as a result, contribute to the total m. The results suggest that the polarization of boron atoms is important in modulating the electron distribution, which may affect the cluster’s reactivity and interactions in different environments.

4. Summary and Conclusions

The successful integration of TM atoms into the core of planar boron clusters B_n creates a fascinating class of borometallic molecules. In our study, we present the results of first-principles calculations aimed at examining the structural, electronic, and magnetic properties of boron rings with a TM atom in the center, TMB_n (with TM being Ti, Cr, Mn, Fe, Co, Nb, or Mo, and n being 8, 9, or 10), as well as boron double-rings sandwiching the metal atom, TMB_2n. In these molecular structures, each B atom in the circumference provides two electrons to the B–B peripheral covalent bonds and one electron to the delocalized B–TM bonds. Consequently, a TM atom with the appropriate number of valence electrons can be accommodated in the center of the boron wheel to form the TMB_n clusters, resulting in a structurally and dynamically stable borometallic cluster compound. Most of the studied clusters also possess relatively high H-L energy gaps, which may suggest low chemical reactivity. Our investigation also indicates that the overall magnetic moment of the clusters is a combination of the magnetic moment of the central TM atom and the induced magnetic moment of the peripheral boron atoms. These molecular-based magnets provide a platform for studying magnetism in the zero-dimensional limit. Furthermore, the TMB_2n clusters can be building blocks for one-dimensional tubular forms.