Synthesis and Structural Study of the Bis(ethylenediamine)CdFe(CO)4 Monomer

The new complex has been isolated from the crystallization of from ethylenediamine (en). The cadmium center bears square-pyramidal coordination, with the iron atom occupying the apical position. The iron coordination may be described either as trigonal bipyramidal, with the cadmium atom being in an axial position, or as monocapped (by cadmium) tetrahedral. The Cd-Fe distance was found to be 2.6250(2)？？. The complex crystallizes in the monoclinic space group with ？？, ？？, ？？, and at 150(1)？K. 1. Introduction Since the first reports of and various base adducts [1, 2], primarily being of the type with L representing chelating or nonchelating amine or ether ligands, surprisingly little effort has been expended toward the investigation of their structural natures, including their degrees of association. To date, most of the ligand adduct complexes have been found to be trimeric, as observed for THF, pyridine, and 2,2′-bipyridine [3, 4], though dimeric species have also been isolated (vide infra), as well as more complicated ring systems [5–7]. In the complexes, oligomerization occurs through the formation of metal-metal bonded rings composed of alternating cadmium and iron atoms. Under the right conditions, additional base coordination can be used to generate monomeric species (Figure 1) [8], which are actually more typical of analogous zinc complexes [2, 8, 9]. For the cadmium complexes, either the use of special chelating ligands, such as tren (2,2′,2′′-triaminotriethylamine), or crystallization from strongly coordinating solvents such as pyridine, can be used to favor the isolation of such monomers [8]. As an example of the latter approach, crystallization of ( ) from pyridine has led to the isolation of (py)(neocuproine) monomers (neocuproine = 2,9-dimethylphenanthroline) [10]. Herein we report that crystallization of the known complex from en (en = ethylenediamine) leads to the formation of monomers, which are especially unusual due to the presence of five-coordinate, square-pyramidal cadmium coordination. Figure 1: Structural illustrations for monomeric complexes. 2. Materials and Methods 2.1. Synthesis All reactions were carried out in Schlenk apparatus under a nitrogen atmosphere. All nonmetallic reagents were obtained commercially, and was prepared by a published procedure [2]. (en = ethylenediamine) was synthesized by adding 20？mL of ethylenediamine to 1？g (3？mmol) of while stirring, leading to complete dissolution of the compound. In order to form crystals, water was added at room temperature until a small amount of precipitate had formed. The