title: 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 a stable CuII-thiolate.
abstract: 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. Isolation of dimeric [Ni(II)(SN4(tren)-RS(dang))]2 ("dang"= dangling, uncoordinated thiolate supported by H bonds), using the less bulky [(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(Me2)N4(tren)]+, are isostructural and adopt a tetragonally distorted trigonal bipyramidal geometry favored by ligand constraints. The nickel complex uniquely adopts an approximately ideal square pyramidal geometry and resembles the active site of Ni-superoxide dismutase (Ni-SOD). Even in coordinating solvents such as MeCN, only five-coordinate structures are observed. The MII-S thiolate bonds systematically decrease in length across the series (Mn-S > Fe-S > Co-S > Ni-S approximately Cu-S < Zn-S) with exceptions occurring upon the occupation of sigma* orbitals. The copper complex, [Cu(II)(S(Me2)N4(tren)]+, represents a rare example of a stable CuII-thiolate, and models the perturbed "green" copper site of nitrite reductase. In contrast to the intensely colored, low-spin Fe(III)-thiolates, the M(II)-thiolates described herein 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 the d-orbitals drop in energy proceeding across the across the series M(2+) (M= Mn, Fe, Co, Ni, Cu), the sulfur-to-metal charge-transfer transition moves into the visible region, and the redox potentials cathodically shift. The reduced M(+1) oxidation state is only accessible with copper, and the more oxidized M(+4) oxidation state is only accessible for manganese.
authors.affiliation: The Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195-1700, USA.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Brines
authors.forename: Jason
authors.initials: J
authors.lastname: Shearer
authors.forename: Jessica K
authors.initials: JK
authors.lastname: Fender
authors.forename: Dirk
authors.initials: D
authors.lastname: Schweitzer
authors.forename: Steven C
authors.initials: SC
authors.lastname: Shoner
authors.forename: David
authors.initials: D
authors.lastname: Barnhart
authors.forename: Werner
authors.initials: W
authors.lastname: Kaminsky
authors.forename: Scott
authors.initials: S
authors.lastname: Lovell
authors.forename: Julie A
authors.initials: JA
authors.lastname: Kovacs
mesh_terms: D009682:Magnetic Resonance Spectroscopy; D008670:Metals / Q000737:chemistry*; D008958:Models, Molecular; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D008670:Metals; D013438:Sulfhydryl Compounds