Stereochemistry of Carbonylmetalloporphyrins. The Structure of (Pyridine)(carbonyl)(5,10,15,20-tetraphenylporphinato)iron(II)

The six-coordinate carbon monoxide complex of an iron(II) porphyrin, Fe(TPP)(CO)(Py) (TPP = 5,10,15,20-tetraphenylporphyrin dianion, Py = pyridine), has been prepared and its structure determined from three-dimensional x-ray diffraction data. The linear (179 (2)°) Fe-C-O arrangement found here is to be contrasted with the bent Fe-C-O arrangements reported for three carbon monoxide hemoproteins. The Fe-C and C-O distances are 1.77 (2) and 1.12 (2) Å, respectively. The average Fe-N (porphyrin) distance is 2.02 (3) Å, somewhat shorter than the Fe-N (Py) distance of 2.10 (1) Å trans to the CO group in this octahedral complex. The Fe atom is displaced only 0.02 Å from the porphyrin N4 plane toward the CO group. The porphyrin core is nearly planar and all bond parameters in the core agree well with those found in other porphyrins. The complex crystallizes with four formula units and eight benzene molecules in the monoclinic space group C_2h ⁵-P2₁/c with a = 13.246 (17), b = 19.555 (26), c = 19.822 (25) Å, and β = 105.49 (3)°. The final agreement indices on F_o ², based on the leastsquares refinement of 205 variables for 3161 observations (including F_o ² ≤ 0), are R = 0.18 and R_w = 0.23. The conventional R index on F_o for reflections with F_o ² ≥ 3σ(F_o ²) is 0.090.