Photoelectron spectroscopy of B4O4−: Dual 3c-4e π hyperbonds and rhombic 4c-4e o-bond in boron oxide clusters

Abstract

Gas-phase anion photoelectron spectroscopy (PES) is combined with global structural searches and electronic structure calculations at the hybrid Becke 3-parameter exchange functional and Lee-Yang-Parr correlation functional (B3LYP) and single-point coupled-cluster with single, double, and perturbative triple excitations (CCSD(T)) levels to probe the structural and electronic properties and chemical bonding of the B4O4 (0/-) clusters. The measured PES spectra of B4O4 (-) exhibit a major band with the adiabatic and vertical detachment energies (ADE and VDE) of 2.64 ± 0.10 and 2.81 ± 0.10 eV, respectively, as well as a weak peak with the ADE and VDE of 1.42 ± 0.08 and 1.48 ± 0.08 eV. The former band proves to correspond to the Y-shaped global minimum of Cs B4O4 (-) ((2)A″), with the calculated ADE/VDE of 2.57/2.84 eV at the CCSD(T) level, whereas the weak band is associated with the second lowest-energy, rhombic isomer of D2h B4O4 (-) ((2)B2g) with the predicted ADE/VDE of 1.43/1.49 eV. Both anion structures are planar, featuring a B atom or a B2O2 core bonded with terminal BO and/or BO2 groups. The same Y-shaped and rhombic structures are also located for the B4O4 neutral cluster, albeit with a reversed energy order. Bonding analyses reveal dual three-center four-electron (3c-4e) π hyperbonds in the Y-shaped B4O4 (0/-) clusters and a four-center four-electron (4c-4e) π bond, that is, the so-called o-bond in the rhombic B4O4 (0/-) clusters. This work is the first experimental study on a molecular system with an o-bond.

Binary B4S4 Rhombic Clusters as Promising Inorganic Ligands for ­Triple‐Decker Sandwich Complexes

“…Here, NICS(0) and NICS zz (1.0) are calculated at the center of the ring and at 1.0 Å above the center, respectively. The similar bonding pattern named o-bond was described recently in the boron oxide clusters, [14,18] boron hydride oxide, and boron hydride sulfide clusters. [19] The global bonding elements are also obvious in the AdNDP pattern.…”

“…For the neutral structures, D 2h B 4 O 4 , with a perfectly planar structure, has been predicted to be the global minimum, which is far more stable than its Yshaped structure. [18] Notably, the global-minimum structures for B 4 S 4 and B 4 O 4 are rather similar except for the distortion of rhombic B 2 S 2 in the former. This similarity also exists in our recent study of B 2 S 2 H 2 and B 2 O 2 H 2 .…”

“…The B 6 O 6 cluster features a boroxol B 3 O 3 ring as the structural core with three boronyl (BO) groups attached terminally, closely resembling boroxine and obtainable from the latter by isovalent BO/H substitution. Interestingly, D 2h B 4 O 4 with a B 2 O 2 core and two terminal boronyl (BO) groups [18] can be obtained from D 2h B 2 O 2 H 2 [19] by isovalent BO/H substitution. Notably, both D 3h B 6 O 6 and D 2h B 2 O 2 H 2 can be used as inorganic ligands to form transitional-metal complexes, such as the sandwich-type D 3d (B 6 O 6 )Cr, [17] D 3d (B 6 O 6 )V, [20] and D 2d [B 2 O 2 H 2 ] 2 Ni.…”

A first-principles study on the B5O5+/0 and B5O5− clusters: The boron oxide analogs of C6H5+/0 and CH3Cl

“…The BO distances within the OBO unit are uneven: 1.23 Å versus 1.29 Å, which are close to the B≡ ≡O and B= =O bonds, respectively. 48,63 The B1-O5 bond should be roughly considered as a single bond, although the distance (1.51 Å) is markedly longer than a typical single bond; see Section IV B for further discussion. The The global-minimum structures 1 and 2 for B 5 O 5 +/0 are rather similar (Fig.…”

“…Such a nonbonding/bonding system is recently described as an o-bond. 46,48 The o-bond differs from a typical 4π antiaromatic system; the latter features an antibonding/bonding combination for the two π CMOs, which leads to a rectangular structural distortion. The HOMO of C 2v ( 1 A 1 ) is also localized around the tetracoordinate B atom, suggesting an approximate "B − " center.…”