Group 6 Complexes with Iron and Zinc Heterometals: Understanding the Structural, Spectroscopic, and Electrochemical Properties of a Complete Series of MM···M′ Compounds

Abstract

Binuclear quadruply bonded complexes Cr(2)(dpa)(4) (1, dpa = 2,2'-dipyridylamide), Mo(2)(dpa)(4) (2), and W(2)(dpa)(4) (3) react with anhydrous FeCl(2), yielding heterometallic compounds CrCrFe(dpa)(4)Cl(2) (4), MoMoFe(dpa)(4)Cl(2) (5), and WWFe(dpa)(4)Cl(2) (6). These molecules are structurally similar, having a linear M≡M···Fe chain that is axially capped by chloride ions and is equatorially supported by the helically twisted dpa ligands. A structurally related zinc analog, CrCrZn(dpa)(4)Cl(2) (7), can be prepared upon metalation of 1 with ZnCl(2). This reaction also persistently produces a 2:1 adduct of ZnCl(2) with 1, [Cr(2)(dpa)(4)](ZnCl(2))(2) (8), which is in equilibrium with 7 and has the two zinc ions bound externally to the Cr(2) core and axial bridging chloro ligands attached to each Cr ion. The sole isolable product of the addition of ZnCl(2) to 3 is a 1:1 adduct, [W(2)(dpa)(4)]ZnCl(2) (9). The structurally related chain complexes 4, 5, 6, and 7 are characterized by X-ray crystallography, UV-vis spectroscopy, cyclic voltammetry, and (57)Fe Mössbauer spectroscopy for the iron complexes in order to gain insights into the nature of heterometallic interactions, electronic excited states, and redox properties of these compounds, which have implications for all other M≡M···M' molecules. Additionally, NMR spectroscopy has been used to gain insight into the mechanism of the metalation of 1 by Zn(II).

From Homonuclear Metal String Complexes to Heteronuclear Metal String Complexes

“…[38][39][40][41] Their work has provided a great insight into HMSCs that may have potential in many important catalytic applications, from heterometallic enzyme active sites to alloys or mixed metal oxides in heterogeneous catalysis.…”

“…The synthetic strategies for the preparation of M A -M A -M B HMSCs reported by Berry. [38][39][40][41]43] . Adapted with permission from ref.…”

“…3 (Cr) [23a] 2.241(3) 2.478(3) 2.117(2) 2.542(1) 31 (Mn) [41] 2.023(4) 2.807(4) 2.197(1) 2.256(1) 32 (Fe) [41] 2.029 (2) 2.703(2) 2.153(2) 2.319(2) 33 (Co HS ) [41] 2.067 (5) 2.623(5) 2.125(3) 2.370(1) 33 (Co LS ) [41] 2.036 (5) 2.491(1) 2.054(2) 2.567(5) 34 (Ni) [41] 2.037 (2) 2.585(2) 2.117(4) 2.360(2) 35 (Zn) [41] 1.996 (1) 2.773(1) 2.155(2) 2.251 (1) [a] Average bond length.…”

Coordination Chemistry of 2,2’-Dipyridylamine: The Gift That Keeps on Giving

“…The heterometallic compounds synthesized to date fall into three classes as has been previously suggested: [40] 1) symmetric M (22), [76] was prepared from the reaction of quadruply bonded Cr 2 (dpa) 4 and divalent FeCl 2 in refluxing THF. [40,77] Mn II , [78] Fe II , [78,79] Co II , [80] Ni II , [81] and Zn II , [79] ions have been made. In most cases, partial σ bonding delocalization throughout the chain is achieved.…”

“…A variable temperature 1 H NMR study on the Cr 2 Zn(dpa)4 Cl 2 compound revealed that the dpa ligand most likely undergoes a longitudinal shuffling, shifting form coordination mode III to mode IV, where the central N a bridges the quadruply bonded metal atoms, to mode III which allows for metalation to occur, scheme 3 [79]. For Cr 2 (dpa)4 , refluxing THF provides enough heat to accomplish this rearrangement.…”