110487-89-3Relevant academic research and scientific papers
Stereochemical and electrochemical characterization of the iron-iron multiple-bonded [Fe2(η5-C5H5-xMe x)2(μ-NO)2]n dimers (x = 0, 1, 5; n = 0, 1-): A structural-bonding analysis of the iron and cobalt nitrosyl-bridged [M2(η5-C ...
Kubat-Martin, Kimberly A.,Barr, Mary E.,Spencer, Brock,Dahl, Lawrence F.
, p. 2570 - 2579 (2008/10/08)
Full title: Stereochemical and electrochemical characterization of the iron-iron multiple-bonded [Fe2(η5-C5H5-xMe x)2(μ-NO)2]n dimers (x = 0, 1, 5; n = 0, 1-): A structural-bonding analysis of the iron and cobalt nitrosyl-bridged [M2(η5-C5H5) 2(μ-NO)2]n series (M = Fe, n = 0, 1-; M = Co, n = 1+, 0). In connection with our previous investigations of the 32/33-electron [Co2(η5-C5R5) 2(μ-CO)2]n series (n = 0, 1-) have carried out structural-bonding studies of the 32-electron Fe2(η5-C5H5-xMe x)2(μ-NO)2 dimers (x = 0, 1, 5) and the 33-electron [Co2(η5-C5H4Me) 2(μ-NO)2]+ monocation. The results reported herein include the following: (1) Cyclic voltammetric measurements showed that the three neutral iron dimers undergo similar one-electron reversible reductions to their respective monoanions. The E1/2 values exhibit a linear change in negative voltage per methyl ring substituent consistent with increased difficulty in reduction upon methyl ring substitution. (2) An X-ray crystallographic determination of the 32-electron Fe2(η5-C5H4Me) 2(μ-NO)2 disclosed a planar Fe2(NO)2 core of crystallographic C2h-2/m site symmetry with an Fe-Fe distance of 2.326 (4) A? which is identical with that in the previously characterized Fe2(η5-C5H5) 2(μ-NO)2. (3) An X-ray crystallographic determination of the 33-electron [Fe2(η5-C5H5) 2(μ-NO)2]- monoanion (isolated as the [PPN]+ salt) showed that the salient geometrical change resulting from the oxidation of the monoanion to its 32-electron neutral parent is a decrease in the Fe-Fe distance from 2.378 (1) (av) to 2.326 (4) A?. This 0.052-A? shortening in the metal-metal distance (upon oxidation) is completely compatible with the unpaired electron in the monoanion occupying a HOMO mainly composed of out-of-plane dπ dimetal-antibonding character. This geometrical change provides an experimental operational test that the isoelectronic [Fe2(η5-C5R5) 2(μ-NO)2]n and [Co2(η5-C5R5) 2(μ-CO)2]n series (n = 0 ,1-) have similar corresponding LUMO's (n = 0) and HOMO s (n = 1-). (4) In light of the previously reported (and theoretically inexplicable) bond-length decrease of 0.05 A? in the mean Co-NO distance upon oxidation of the 34-electron Co2(η5-C5H5) 2(μ-NO)2 neutral parent to its 33-electron monocation, a crystallographic determination of the corresponding [Co2(η5-C5H4Me) 2(μ-NO)2]+ monocation (isolated as the [PF6]- salt) was performed. An examination of the centrosymmetric Co2(NO)2 cores in these C5H4Me- and C5H5-containing dimers revealed abnormally elongated out-of-plane thermal ellipsoids for the nitrogen and oxygen atoms in both monocations We propose that the similarly short mean Co-NO bond lengths in these monocations are due in large part to an artifact of crystal disorders involving a superposition of at least two nonplanar orientations for each nitrosyl ligand; hence, the actual Co-NO bond lengths in these cobalt monocations may not be smaller than those in their neutral parents. Fe2(η5-C5H4Me) 2(μ-NO)2: Mr 329.95; monoclinic; C2/m; a = 7.966 (4) A?, b = 8.644 (2) A?, c = 9.833 (4) A?, β = 113.36 (3)°, V = 621.6 (4) A?3 at T = 233 K; dcalcd = 1.76 g/cm3 for Z = 2; anisotropic least-squares refinement converged at R1(F) = 7.3% and R2(F) = 8 9% for 737 independent reflections (I > 2.0σ(I)). [(PPh3)2N]+[Fe2(η 5-C5H5)2(μ-NO)2] -: Mr 840.19; triclinic; P1; a = 11.266 (4) A?, b = 17.613 (4) A?, c = 10.362 (4) A?, α = 102.06 (3)° β = 93.17 (3)°, γ = 92.06 (2)°, V = 2005 (1) A? at T = 295 K; dcalcd = 1.39 g/cm3 for Z = 2; anisotropic least-squares refinement for one independent cation and two independent half-anions of Ci-1 site symmetries converged at R1(F) = 4.3% and R2(F) = 5.7% for 4174 independent reflections (I > 2σ(I)). [Co2(η5-C5H4Me) 2(μ-NO)2]+[PF6]-: Mr 481.09; monoclinic; C2/c; a = 17.07 (1) A?, b = 7.530 (8) A?, c = 14.51 (1) A?, β = 113.51 (6)°; V = 1708 (3) A?3 at T = 203 K; dcalcd = 1.87 g/cm3 for Z = 4; anisotropic least-squares refinement converged at R1 (F) = 8.5% and R2(F) = 10.7% for 1194 independent data (I > 1.5σ(I)).
