Abstract
The complex cation in the title compound, (carbonyl-1κC)(1η5-penta-methyl-cyclo-penta-dien-yl)(μ-2,3,9,10-tetra-methyl-1,4,8,11-tetra-thia-undeca-2,9-diene-1,11-diido-1κ2S,S''':2κ4S,S',S'',S''')ironnickel(Fe-Ni) hexa-fluoro-phosphate, [FeNi(C10H15)(C11H18S4)(CO)]PF6 or [Ni(L')FeCp*(CO)]PF6, is composed of the nickel complex fragment [Ni(L')] coordinated as a metalloligand (using S1 and S4) to the [FeCp*(CO)]+ fragment, where (L')2- is [S-C(Me)=C(Me)-S-(CH2)3-S-C(Me)=C(Me)-S]2- and where Cp*- is cyclo-C5(Me)5- (penta-methyl-cyclo-penta-dien-yl). The ratio of hexa-fluoro-phosphate anion per complex cation is 1:1. The structure at 150 K has ortho-rhom-bic (Pbcn) symmetry. The atoms of the complex cation are located on general positions (multiplicity = 8), whereas there are two independent hexa-fluoro-phosphate anions, each located on a twofold axis (Wyckoff position 4c; multiplicity = 4). The structure of the new dimetallic cation [Ni(L')FeCp*(CO)]+ can be described as containing a three-legged piano-stool environment for iron [Cp*Fe(CO)'S2'] and an approximately square-planar 'S4' environment for Ni. The NiS2Fe diamond-shaped substructure is notably folded at the S-S hinge: the angle between the NiS2 plane and the FeS2 plane normals is 64.85 (6)°. Largely because of this fold, the nickel-iron distance is relatively short, at 2.9195 (8) Å. The structural data for the complex cation, which contains a new unsaturated 'S4' ligand (two C=C double bonds), provide an inter-esting comparison with the known NiFe hydrogenase models containing a saturated 'S4'-ligand analogue having the same number of carbon atoms in the ligand backbone, namely with the structures of [Ni(L)FeCp(CO)]+ (as the PF6- salt, CH2Cl2 solvate) and [Ni(L)FeCp*(CO)]+ (as the PF6- salt), where (L)2- is [S-CH2-CH2-S-(CH2)3-S-CH2-CH2-S]2- and Cp- is cyclo-penta-dienyl. The saturated analogues [Ni(L)FeCp(CO)]+ and [Ni(L)FeCp*(CO)]+ have similar Ni-Fe distances: 3.1727 (6), 3.1529 (7) Å (two independent mol-ecules in the unit cell) and 3.111 (5) Å, respectively, for the two complexes, whereas [Ni(L')FeCp*(CO)]+ described here stands out with a much shorter Ni-Fe distance [2.9196 (8) Å]. Also, [Ni(L)FeCp(CO)]+ and [Ni(L)FeCp*(CO)]+ show inter-planar fold angles that are similar between the two: 39.56 (5), 41.99 (5) (independent mol-ecules in the unit cell) and 47.22 (9) °, respectively, whereas [Ni(L')FeCp*(CO)]+ possesses a much more pronounced fold [64.85 (6)°]. Given that larger fold angles and shorter Ni-Fe distances are considered to be structurally closer to the enzyme, unsaturation in an 'S4'-ligand of the type (S-C2-S-C3-S-C2-S)2- seems to increase structural resemblance to the enzyme for structural models of the type [Ni('S4')FeCp R (CO)]+ (Cp R = Cp or Cp*).
Highlights
E74, 1222–1226 research communications and closer structural models for the NiFe hydrogen-splitting active site (Lubitz et al, 2014). This active site contains two terminal sulfur donors and two bridging sulfur donors coordinated to nickel, as well as a pseudo-octahedal coordination sphere around iron, which is completed by cyano and carbonyl ligands (Fig. 1, left)
Several closely related models of the active site have been prepared by combining an Ni(‘S4’) fragment (‘S4’ = dianionic tetradentate sulfur ligand) with an [FeCpR(CO)]+ fragment (CpR = Cp, C5H5 or Cp*, C5Me5), as illustrated in Fig. 1 (Canaguier et al, 2010; Yang et al, 2015; Zhu et al, 2005)
The atoms of the complex cation are situated on general positions, whereas there are two independent hexafluorophosphate anions, each situated on a twofold axis (Wyckoff position 4c in Pbcn; multiplicity = 4)
Summary
Since the discovery and structural elucidation of nickel–iron hydrogenases, synthetic chemists have worked towards closer. The structures of [Ni(L)FeCp(CO)]+, as the PF6À salt/ CH2Cl2 solvate (Zhu et al, 2005), and [Ni(L)FeCp*(CO)]+, as the PF6À salt (Yang et al, 2015), are known Both saturated analogues [Ni(L)FeCp(CO)]+ and [Ni(L)FeCp*(CO)]+ show Ni—Fe distances that are similar for the two, 3.1727 (6)/ 3.1529 (7) A (two independent molecules in the unit cell) and 3.111 (5) A , respectively, for the two complexes. (Zhu et al, 2005) Within the context of linear ‘S4’ ligands, an [Ni(L00)FeCp*(CO)]+ model with four carbon atoms, instead of three, in the remote portion of the backbone (see L002À, right) provided an Ni—Fe distance and fold angle very similar to those of the L0 analogue, of 2.9611 (8) Aand 62.48 (4), respectively (Canaguier et al, 2010). We conclude that the introduction of unsaturation in the ‘S4’ ligand led to a better structural model relative to the unsaturated ligand, highlighting a new variant of the classic [Ni(’S4’)FeCpR(CO)]+-type hydrogenase model
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Acta crystallographica. Section E, Crystallographic communications
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
