title: 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.
authors.affiliation: School of Physical Science and Technology, Southwest Jiaotong University.|Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Chengdu, 610031, China.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Wang
authors.affiliation: School of Physical Science and Technology, Southwest Jiaotong University.|Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Chengdu, 610031, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Chemistry and Center for Computational Chemistry, University of Georgia, Athens, Georgia, 30602.
authors.forename: R Bruce
authors.initials: RB
authors.lastname: King
authors.affiliation: Department of Chemistry and Center for Computational Chemistry, University of Georgia, Athens, Georgia, 30602.
authors.forename: Henry F
authors.initials: HF
authors.lastname: Schaefer
keywords: azulene; density functional theory; first row transition metals; metal-metal bonding; sandwich compounds