Bis(azulene) “submarine” metal dimer sandwich compounds (C₁₀H₈)₂M₂ (M = Ti, V, Cr, Mn, Fe, Co, Ni): Parallel and opposed orientations

Abstract

The opposed and parallel structures for the binuclear bis(azulene) "submarine" sandwiches (C10H8)2M2 (M = Ti, V, Cr, Mn, Fe, Co, Ni) have been optimized using density functional theory. The lowest energy (C10H8)2 M2 structures of the early transition metals Ti, V, Cr, and Mn have the azulene units functioning as bis(pentahapto) ligands to each metal atom similar to the azulene ligand in the long-known molybdenum carbonyl complex (η(5),η(5)-C10H8 )Mo2 (CO)6 . The metal-metal bonds in these early transition metal structures have distances and Wiberg bond indices consistent with the formal bond orders required to give each metal atom an 18-electron configuration for the singlet structures and a 17-electron configuration for the triplet structures. For the later transition metals Fe, Co, and Ni, the lowest energy (C10H8)2 M2 structures contain pentahapto-trihapto azulene ligands with an uncomplexed C=C double bond, similar to that in the long-known iron carbonyl complex (η(5),η(3)-C10H8)Fe2 (CO)5 . The parallel (η(5),η(3)-C10H8 )2M2 (M = Fe, Co, Ni) structures contain metallocene subunits with their metal atoms at long nonbonding distances of 3.5-3.9 Å from the other metal atom, which is located between the azulene C7 rings. Higher energy opposed (C10H8)2 Fe2 structures contain an unprecedented distorted η(6) ,η(4) -azulene ligand using six carbon atoms for bonding to one iron atom as a hexahapto fulvene ligand and the remaining four carbon atoms for bonding to the other iron atom as a tetrahapto diene ligand.

Ironing out the photochemical and spin-crossover behavior of Fe(II) coordination compounds with computational chemistry

“…This remarkably simple reparameterization has generally minor effects on other thermodynamical parameters, based on the G2 test set, compared to the significant effect it had on spin-state splittings. While it is understood that B3LYP* is also not a universally accurate functional, it still has been demonstrated to be highly successful in many varied contexts, and is still routinely used[140][141][142][143][144][145].…”

Effect of Spectator Ligands on Haptotropic Rearrangements of Metal‐Azulene Complexes

“…The metal centre can bond to both rings simultaneously, forming η 5 + 1 , η 5 + 2 and η 7 + 2 bonds. [15,[34][35][36][37] Korichi et al have reported the relative energy of the isomers of several mononuclear Az complexes. Their results do not show a clear trend on the preference of the metal for one of the two rings.…”