Stereochemistry of tetrahedral complexes of group VIII metals. Crystal and molecular structures of dinitrosylcarbonyltriphenylphosphineiron, Fe(NO)2(CO)(PPh3), and of dinitrosylbis(triphenylphosphine)iron, Fe(NO)2(PPh3)2

Single crystal X-ray structures of Fe(NO)2(CO)(PPh3) (I) and of Fe(NO)2(PPh3)2 (II) have been determined. Compound (I) form triclinic crystals of space group P 1 , with cell constants a 10.96(1)», b 10.20(1)», c 10.45(1)», α 115.84(8)°, β 117.33(8)°, γ 78.90(8)°, U 933.4»3, Z 2. Compound (II) forms monoclinic crystals of space group P2/c with cell constants a 11.70(1) », b 8.20(1) » c 17.24(2) », β 106.60(8)°, U 1584.6 »3, Z 2. Both cystals contain discrete molecules of distorted tetrahedral geometry. In compound (I) the CO and NO ligands are disordered; the principal bonding parameters are: FeC/N 1.709 », C/NO 1.148 », FeC/NO 177.9°, FeP 2.260(3) », C/NFeC/N 103.9° and PFeC/N 114.4°. In compound (II), which possesses C2 symmetry, the principal bonding parameters are: N 1.650(7) », NO 1.19(1) », FeNO 178.2(7)° NFeN 123.8(4)°, FeP 2.267(2) », PFeP 111.9(1)°. These values are compared with those found in other tetrahedral complexes of Group VIII metals and discussed in terms of π metalligand interactions.