First-Row Transition Metals in Binuclear Cyclopentadienylmetal Derivatives of Tetramethyleneethane: η³,η³ versus η⁴,η⁴ Ligand–Metal Bonding Related to Spin State and Metal–Metal Bonds

Abstract

The tetramethyleneethane (TME) ligand is found in the η3,η3 complex trans-(η3,η3-TME)Ni2Cp2 and the η4,η4 complex trans-(η4,η4-TME)Co2Cp2, which have both been synthesized and structurally characterized by X-ray crystallography. The structures of the complete series of (TME)M2Cp2 derivatives of the first-row transition metals from Ti to Ni have now been investigated by density functional theory. The experimentally known nickel and cobalt complexes are found to have closed-shell electronic ground states. The lowest energy structure for the iron complex is the triplet spin state trans-(η4,η4-TME)Fe2Cp2 structure with geometry similar to that of the lowest energy cobalt structure. All of the low-energy (TME)M2Cp2 structures for manganese and the first-row transition metals to the left of manganese (Cr, V, and Ti) exhibit cis-(η4,η4-TME)M2Cp2 stereochemistry, thereby providing the possibility for direct metal–metal interactions. Vanadium is the only first-row transition metal to the left of cobalt where the lowest energy (TME)M2Cp2 structure is a singlet spin state, suggesting limited applicability of the 18-electron rule in these systems. The frontier molecular orbitals of these cis-(η4,η4-TME)M2Cp2 systems have been examined in order to provide insight regarding metal–metal bonding. Thus, low-energy cis-(η4,η4-TME)Mn2Cp2 structures are found in both quintet and triplet spin states with formal MnMn double bonds. The lowest energy cis-(η4,η4-TME)Cr2Cp2 and cis-(η4,η4-TME)Ti2Cp2 structures have triplet spin states with a formal CrCr triple bond and a formal TiTi double bond, respectively. The lowest energy cis-(η4,η4-TME)V2Cp2 structure is a singlet structure with a formal VV triple bond.

Binuclear Lantern Complexes of All First-Row 3d Metals Scandium to Zinc: Metal–Metal Bond Lengths and Bond Orders, with Measures of Intrinsic Metal–Metal Bond Strength

“…Triplet ground states are also predicted for Co 2 L 4 and Cu 2 L 4 . For Co 2 L 4 (11), the triplet ground state agrees with previous DFT results, 18 but conflicts with the diamagnetism noted for some known tetragonal dicobalt lanterns. 35 The energy gap between the singlet and triplet states of 11 is narrow, so this prediction of a triplet ground state may not be definitive.…”

“…10 A series of binuclear complexes (TME)M 2 Cp 2 (M = Ti to Ni; TME = tetramethyleneethane; Cp = cyclopentadienyl) was studied using DFT, and the structures were examined and compared. 11 A series of tris(benzene)dimetal complexes (C 6 H 6 ) 3 M 2 (M = Ti to Ni) was studied using DFT to examine the metal−metal bonding and the scope for adopting a triple-decker sandwich or a rice ball structure. 12 Structures and MM bonding in a series of binuclear complexes with the formula (L 3 M) 2 (Phn) (M = Sc to Ni, L = CO, PH 3 /L 3 = Cp; Phn = phenazine ligand) were studied using DFT with the BP86 functional.…”

Machine learning for electronically excited states of molecules

“…are common in transition metal complexes, where an important task is to identify which multiplicity yields the lowest energy and is thus the ground state. 15 refs [16][17][18][19] give a good overview of such processes.…”

Machine Learning for Electronically Excited States of Molecules

“…14 − 17 We note that electron detachment or uptake further leads to doublet and quartet states, and even higher spin multiplicities, such as quintets, sextets, etc. are common in transition metal complexes, where an important task is to identify which multiplicity yields the lowest energy and is thus the ground state; 17 see, e.g., refs ( 18 − 21 ).…”

“…In doing so, we concentrate on singlet and triplet states of molecular systems since almost all existing approaches of ML for the excited states focus on singlet states and only a few studies consider triplet states. − We note that electron detachment or uptake further leads to doublet and quartet states, and even higher spin multiplicities, such as quintets, sextets, etc. are common in transition metal complexes, where an important task is to identify which multiplicity yields the lowest energy and is thus the ground state; see, e.g., refs − .…”