title: Sulfur bridging interactions of cis-planar NiII-S2N2 coordination units with nickel(II), copper(I,II), zinc(II), and mercury(II): a library of bridging modes, including NiII(micro2-SR)2MI,II rhombs.
abstract: Sulfur bridging interactions between three cis-planar NiII-S2N2 complexes and NiII, CuI,II, ZnII, and HgII reactants were investigated by synthesis and X-ray crystal structures of some 24 complexes. This work was stimulated by recent crystallographic structures of the A-cluster of carbon monoxide dehydrogenase/acetylcoenzyme A synthase. This bridged biological assembly has the minimal formulation [Fe4S4]-(micro2-SCys)-[M((micro2-SCys)2Gly)Ni] with M = NiII, CuI, and ZnII at sites distal and proximal, respectively, to the iron-sulfur cluster. Bridges supported by representations of the distal nickel site were sought by reactions of the complexes [NiII(LH-S2N2)]2- and [NiII(LR-S2N2)], with 5-5-5 chelate ring patterns. Reaction products implicate the bridges Ni-(micro2-S)1,2-M in a variety of molecular structures, some with previously unknown connectivities of bridge atoms. The most frequently encountered bridge units are the nonplanar rhombs Ni(2-S)2M involving both sulfur atoms of a given complex. Those with M = NiII are biologically relevant inasmuch as the catalytic metal at the proximal site is nickel. The complex [Ni(L-655)]2-, containing the 6-5-5 ring pattern and coordination sphere of the distal nickel site, was prepared and structurally characterized. It was shown to sustain Ni2(micro2-S)2 rhombic interactions in the form of trinuclear [[Ni(L-655)]2Ni]2- and [[Ni(L-655)]Ni(R2PCH2CH2PR2)] (R = Et, Ph) in which the second NiII simulates the proximal site. Bridging interactions of NiII-S2N2 complexes are summarized, and geometrical features of Ni2(2-S)2 rhombs in these complexes, as dependent on ring patterns, are considered (LH-S2N2 = N,N'-ethylenebis(2-mercaptoisobutyramide)(4-); LR-S2N2 = trans-rac-N,N'-bis(2-mercapto-2-methylprop-1-yl)-1,2-cyclohexanediamine(2-); L-655 = N-(2-mercaptopropyl)-N'-(2'-mercaptoethyl)glycinamide(4-)).
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: P Venkateswara
authors.initials: PV
authors.lastname: Rao
authors.forename: Sumit
authors.initials: S
authors.lastname: Bhaduri
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Jiang
authors.forename: R H
authors.initials: RH
authors.lastname: Holm
mesh_terms: D001952:Bridged-Ring Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007501:Iron / Q000737:chemistry; D008628:Mercury / Q000737:chemistry; D008968:Molecular Conformation; D009532:Nickel / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D012834:Silver / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D001952:Bridged-Ring Compounds; D009942:Organometallic Compounds; D012834:Silver; D013455:Sulfur; D003300:Copper; D009532:Nickel; D007501:Iron; D008628:Mercury; D015032:Zinc; D009584:Nitrogen