Periodic Trends within a Series of Five-Coordinate Thiolate-Ligated [MII(SMe2N4(tren))]+ (M = Mn, Fe, Co, Ni, Cu, Zn) Complexes, Including a Rare Example of

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• 作者：Lisa M. Brines ; Jason Shearer ; Jessica K. Fender ; Dirk Schweitzer ; Steven C. Shoner ; David Barnhart ; Werner Kaminsky ; Scott Lovell ; Julie A. Kovacs
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：October 29, 2007
• 年：2007
• 卷：46
• 期：22
• 页码：9267 - 9277
• 全文大小：243K
• 年卷期：v.46,no.22(October 29, 2007)
• ISSN：1520-510X

文摘

A series of five-coordinate thiolate-ligated complexes [M^II(tren)N₄S^Me2]⁺ (M = Mn, Fe, Co, Ni, Cu, Zn; tren =tris(2-aminoethyl)amine) are reported, and their structural, electronic, and magnetic properties are compared. Isolationof dimeric [Ni^II(SN₄(tren)-RS^dang)]₂ ("dang"= dangling, uncoordinated thiolate supported by H bonds), using the lessbulky [(tren)N₄S]^1- ligand, pointed to the need for gem-dimethyls adjacent to the sulfur to sterically prevent dimerization.All of the gem-dimethyl derivatized complexes are monomeric and, with the exception of [Ni^II(S^Me2N₄(tren)]⁺, areisostructural and adopt a tetragonally distorted trigonal bipyramidal geometry favored by ligand constraints. Thenickel complex uniquely adopts an approximately ideal square pyramidal geometry and resembles the active siteof Ni-superoxide dismutase (Ni-SOD). Even in coordinating solvents such as MeCN, only five-coordinate structuresare observed. The M^II-S thiolate bonds systematically decrease in length across the series (Mn-S > Fe-S >Co-S > Ni-S ~ Cu-S < Zn-S) with exceptions occurring upon the occupation of * orbitals. The copper complex,[Cu^II(S^Me2N₄(tren)]⁺, represents a rare example of a stable Cu^II-thiolate, and models the perturbed "green" coppersite of nitrite reductase. In contrast to the intensely colored, low-spin Fe(III)-thiolates, the M(II)-thiolates describedherein are colorless to moderately colored and high-spin (in cases where more than one spin-state is possible),reflecting the poorer energy match between the metal d- and sulfur orbitals upon reduction of the metal ion. As thed-orbitals drop in energy proceeding across the across the series M²⁺ (M= Mn, Fe, Co, Ni, Cu), the sulfur-to-metalcharge-transfer transition moves into the visible region, and the redox potentials cathodically shift. The reducedM⁺¹ oxidation state is only accessible with copper, and the more oxidized M⁺⁴ oxidation state is only accessible formanganese.