Structural variations, electrochemical properties and computational studies on monomeric and dimeric Fe–Cu carbide clusters, forming copper-based staple arrays

Abstract

The halide ligands of [Fe(4)C(CO)(12)(CuCl)(2)](2-) (1) and [Fe(5)C(CO)(14)CuCl](2-) (2) can be displaced by N-, P- or S-donors. Beside substitution, the clusters easily undergo structural rearrangements, with loss/gain of metal atoms, and formation of Fe(4)Cu/Fe(4)Cu(3) metallic frameworks. Thus, the reaction of 1 with excess dppe yielded [{Fe(4)C(CO)(12)Cu}(2)(μ-dppe)](2-) (3). [{Fe(4)C(CO)(12)Cu}(2)(μ-pyz)](2-) (4) was obtained by reaction of 2 with Ag(+) and pyrazine. [Fe(4)C(CO)(12)Cu-py](-) (5) was formed more directly from [Fe(4)C(CO)(12)](2-), [Cu(NCMe)(4)](+) and pyridine. [Fe(4)Cu(3)C(CO)(12)(μ-S(2)CNEt(2))(2)](-) (6) and [{Fe(4)Cu(3)C(CO)(12)(μ-pz)(2)}(2)](2-) (7) were prepared by substitution of the halides of 1 with diethyldithiocarbamate and pyrazolate, in the presence of Cu(i) ions. All of these products were characterized by X-ray analysis. 3 and 4 and 5 are square based pyramids, with iron in the apical sites, the bridging ligands connect the two copper atoms in 3 and 4. 6 and 7 are octahedral clusters with an additional copper ion held in place by the two bridging anionic ligands, forming a Cu(3) triangle with Cu-Cu distances ranging 2.63-3.13 Å. In 7, an additional unbridged cuprophilic interaction (2.75 Å) is formed between two such cluster units. DFT calculations were able to reproduce the structural deformations of 3-5, and related their differences to the back-donation from the ligand to Cu. Additionally, DFT found that, in solution, the tight ion pair [NEt(4)](2)7 is almost isoenergetic with the monomeric form. Thus, 3, 4 and 7 are entities of nanometric size, assembled either through conventional metal-ligand bonds or weaker electrostatic interactions. None of them allows electronic communication between the two monomeric units, as shown by electrochemistry and spectroelectrochemical studies. (dppe = PPh(2)CH(2)CH(2)PPh(2), pyz = pyrazine C(4)N(2)H(4), py = pyridine C(5)H(5)N, pz = pyrazolate C(3)N(2)H(3)(-)).

A dimer of the negatively charged carbonyl cluster {Ir4(CO)11−}2 bonded by a single Ir−Ir bond, and comparison with the singly bonded (C60−)2 dimer.

“…As a result, only cationic surrounding can stabilize the {Ir 4 (CO) 11 − } 2 dimers, and they can be obtained in the presence of counter cations only. Previously, it was even shown that the anion‐cation association can stabilize dimers even with very weak intermetallic interactions [19] …”

“…Previously, it was even shown that the anioncation association can stabilize dimers even with very weak intermetallic interactions. [19] The observed difference the formation of neutral and anionic dimers is a result of the intramolecular Coulomb repulsion between negative charges localized on the {Ir 4 (CO) 11 À } units within the dimers. Optimization of the dimer with a fixed long IrÀ Ir bond distance of 30 Å, when there is no any chemical interaction between the iridium atoms, gives the repulsion energy of 15.4 kcal/mol.…”

Synthesis of the Highly Reduced [Fe6C(CO)15]4– Carbonyl Carbide Cluster and Its Reactions with H+ and [Au(PPh3)]+

“…Thereafter, other carbonyliron carbide clusters were discovered, and they may be grouped into three main categories: (1) tetrairon clusters with a butterfly structure and a semi‐exposed carbide, such as [Fe 4 C(CO) 13 ], [Fe 4 C(CO) 12 ] 2– , [HFe 4 C(CO) 12 ] – ,, [HFe 4 CH(CO) 12 ]; (2) pentairon clusters with a square‐pyramidal structure and a basal semi‐exposed carbide, for example, [Fe 5 C(CO) 15 ], [Fe 5 C(CO) 14 ] 2– ; (3) the hexairon octahedral [Fe 6 C(CO) 16 ] 2– cluster featuring a fully interstitial carbide atom. Iron carbide clusters have been thoroughly investigated and represented milestones for the understanding of the reactivity and activation of CO and carbides on metal surfaces and nanoclusters, leading to major contributions to the development of the cluster‐surface analogy Moreover, they have been widely employed for the preparation of miscellaneous dimetallic carbonyl carbide clusters …”