Effect of the Sixth Axial Ligand in CS-Ligated Iron(II)octaethylporphyrinates:  Structural and Mössbauer Studies

Abstract

The effect of a sixth ligand in a series of low-spin thiocarbonyl-ligated iron(II)octaethylporphyrinates has been investigated. Six-coordinate complexes have been synthesized and characterized by Mössbauer and infrared spectroscopy and single-crystal X-ray structure determinations. The results are compared with the five-coordinate parent complex. The crystal structures of [Fe(OEP)(CS)(1-MeIm)] and [Fe(OEP)(CS)(Py)] are reported and discussed. The 1-methylimidazole and pyridine derivatives exhibit Fe-C(CS) bond distances of 1.703(4) and 1.706(2) A that are significantly longer than the 1.662(3) A reported for five-coordinate [Fe(OEP)(CS)] (Scheidt, W. R.; Geiger, D. K. Inorg. Chem. 1982, 21, 1208). The trans Fe-N(ligand) distances of 2.112(3) and 2.1550(15) A observed for the 1-methylimidazole and pyridine complex are approximately 0.13 A longer than those observed for analogous bis-ligated complexes and are consistent with a significant structural trans effect for the CS ligand. Mössbauer investigations carried out for five- and six-coordinate thiocarbonyl derivatives with several different sixth axial ligands reveal interesting features. All derivatives exhibit very small isomer shift values, consistent with a very strong interaction between iron and CS. The five-coordinate derivative has delta(Fe) = 0.08 mm/s, and the six-coordinate complexes exhibit delta(Fe) = 0.14 to 0.19 mm/s at 4.2 K. The five-coordinate complex shows a large quadrupole splitting (DeltaE(q) = 1.93 mm/s at 4.2 K) which is reduced on coordination of the sixth ligand (DeltaE(q) = 0.42-0.80 mm/s at 4.2 K). Addition of a sixth ligand also leads to a small decrease in the value of nu(CS). Correlations in structural, IR, and Mössbauer results suggest that the sixth ligand effect is primarily induced by changes in sigma-bonding. The structure of [Fe(OEP)(CS)(CH(3)OH)] is briefly reported. Crystal data: [Fe(OEP)(CS)(1-MeIm)] crystallizes in the monoclinic system, space group P2(1)/n, Z = 4, a = 9.5906(5) A, b = 16.704(4) A, c = 23.1417(6) A, beta = 100.453(7) degrees. [Fe(OEP)(CS)(Py)] crystallizes in the triclinic system, space group P1, Z = 5, a = 13.9073(6) A, b = 16.2624(7) A, c = 22.0709(9) A, alpha = 70.586(1) degrees, beta = 77.242(1) degrees, gamma = 77.959(1) degrees. [Fe(OEP)(CS)(CH(3)OH)] crystallizes in the triclinic system, space group P1, Z = 1, a = 9.0599(5) A, b = 9.4389(5) A, c = 11.0676(6) A, alpha = 90.261(1) degrees, beta = 100.362(1) degrees, gamma = 114.664(1) degrees.

New Insights on the Electronic and Molecular Structure of Cyanide-Ligated Iron(III) Porphyrinates

“…Similar differences are seen in carbonyl or thiocarbonyl complexes with pyridines or imidazoles trans to the CO [58,59,60] or CS. [61] The effect of differing trans bond distances is likely the difference that imidazoles are modest π-electron-donors compared to the modest π-accepting character of pyridine. [62,63] Clearly, one can expect that the cyanide and pyridine will compete for the same iron π density whereas the imidazole can π-donate and hence form a stronger bond.…”

Ligand effect on the periodic properties of trivalent organolanthanide complexes: a density functional study

“…It has been observed that certain characteristics, e.g., atomic/ionic radii [2], and bond length as well as hardness [2,7], of lanthanide compounds show irregular patterns, i.e., a smooth trend is not followed. Unfortunately, to the best of our knowledge, the influence of ligands on the periodic properties of organolanthanides is not noticed so far although ligand effect was found to affect the structure and activity of transition metal complexes [8,9]. It is also noteworthy here that density functional theory (DFT) calculations performed on certain lanthanide complexes [2,[10][11][12] show the significance of relativistic effects.…”

Electronic Configuration and Ligand Nature of Five-Coordinate Iron Porphyrin Carbene Complexes: An Experimental Study

“…The relatively large iron out of plane displacements (Δ 24 and Δ 4 ) and the longer Fe–C carbene distances of the two [Fe­(TFPP) (CPh 2 )] structures are also consistent with the steric effect of CPh 2 . The key structural parameters of the well-studied, low spin [Fe­(II) (Porph) (XY)] (XY = CO, CS and CN – ) are also given in Table . It is seen the Δ 24 (and Δ 4 ), and the (Fe–N p ) av distances of the carbene complexes are in the range of 0.17–0.30 and 1.96–1.99 Å.…”