Electronic Structure of Metal—Metal Bonds

Abstract

The nature of bonding between two metal centres is extremely variable, spanning formal bond orders from 1 to 6, and this leads to a great diversity of chemical properties in metal cluster compounds. The bonds themselves have components with σ, π, δ, and ϕ symmetry, each of which has its own distinct properties. This article reviews the key features of these different bonding components.

Covalent vs Charge-Shift Nature of the Metal–Metal Bond in Transition Metal Complexes: A Unified Understanding

“…The metal–metal (M–M) bond in transition metal (TM) complexes can be considered as a potential candidate for CSB, as the semicore ( n – 1)­s 2 ( n – 1)­p 6 electrons create excessive Pauli repulsion pressure in the bonding region, just like the σ-lone pairs in F 2 . Note that we label for convenience the semicore orbitals as ( n – 1)­s, ( n – 1)­p, and valence as ( n - 1)­d, and ns for a metal atom belonging to the n th period of the Periodic Table.…”

Fine-Tuning of Magnetic Properties in Nickel(II) Trinuclear EMACs via Modifications of Equatorial Ligands

“…Next in the energy scale above 5 Q is the triplet at terminal site, 3 T, which is higher by 0.15 eV (in case of dpa 0.35 eV, and 0.90 eV for deta), followed by singlet, 1 Σ, 0.72 eV (dpa is 1.41 eV, and deta is 2.16 eV). The dtrza ligand has additional excited triplet, 3 T′, and quintet states solutions, 5 Q′, with the HS central nickel atom, that we failed to locate for the dpa complex. They are respectively 0.92 and 1.39 eV higher from the reference quintet state solution (a corresponding triplet in deta complex is 3.21 eV higher).…”

“…Proper understanding of structure–activity relationship is essential for new innovative design, utilizing full potential and complexity of these hybrid molecules. The linear 1D chains of transition metal atoms (extended metal atom chain, EMAC) supported on an organic multidentate ligands − are an excellent example of such hybrid materials. The oligopyridylamine ligands, such as dipyridyloamine ( dpa ), or similar, containing pyridyl and amine nitrogen atoms, have been used in general to synthesize various metal string complexes, reported so far. − Some modifications include pyrazine instead of pyridine rings, , pyridine substituted with N -sulfonyl based groups or acetamide groups, − naphtyridyne groups, or rigid 1,9-diazaphenoxazine units .…”

“…The linear 1D chains of transition metal atoms (extended metal atom chain, EMAC) supported on an organic multidentate ligands − are an excellent example of such hybrid materials. The oligopyridylamine ligands, such as dipyridyloamine ( dpa ), or similar, containing pyridyl and amine nitrogen atoms, have been used in general to synthesize various metal string complexes, reported so far. − Some modifications include pyrazine instead of pyridine rings, , pyridine substituted with N -sulfonyl based groups or acetamide groups, − naphtyridyne groups, or rigid 1,9-diazaphenoxazine units . Ligand modifications are introduced in order to diversify the transition metal atom constituents via metal–ligand specific interactions, to extend the length of metal chains and to affect the electronic properties of EMACs.…”

“…The Ni­(II)-based chain complexes are one of the most extensively studied, by both experimental and theoretical methods. − Among them the trinuclear species are best understood, providing suitable amount of data for comparison, therefore we have chosen the trimetal [Ni 3 ] 6+ core in order to examine ligand effects. The nickel­(II) EMACs are characterized by two magnetically active terminal centers, while the metal ions in the middle of the chain are diamagnetic (square-planar, four-coordinated), with weak interactions between Ni­(II) ions in the chain. ,,, In the following part, the coordination environment provided by aliphatic amino-nitrogen atoms is compared with the aromatic amines to discuss the influence of equatorial ligands on the electronic structure and magnetic properties of trinickel metal chains.…”