Structural and Gas Uptake Studies on Iron(II) β‑Diketiminate Metallomacrocycles

Abstract

Three iron metallomacrocycles were synthesized and characterized using single crystal X-ray crystallography. Varying the amide coligand allows for macrocycles containing three, four, or six iron centers. The metallomacrocycles show extended structures in the solid state that are reminiscent of metal-organic framework structures; thus, the adsorbative properties of the complexes in the solid state have been investigated using N₂. Based on the data, three metallomacrocyles display classical type II isotherms and pore size distributions synonymous with mesoporous materials.

1. (a) Ogura and Co-Worker’s Synthesis of the First Metallomacrocyclic Species; (b) Holland and Co-Worker’s Synthesis of a β-Diketiminate Fe­(II)-Based Macrocycle via C–N Bond Cleavage; (c) Hypothesized Synthesis of Iron-Containing Metallocycles by N–H Activation of Amides Bearing Coordinating Atoms

1

Molecular structure of Fe-3 (CCDC 1962467). Ellipsoids are represented at a 30% probability. Hydrogen atoms have been omitted, and the β-diketiminate substituents have been represented in wireframe view, for clarity. Symmetry operations¹:1–z, 1–x, – y ²;1–y, – z, 1–x ³;2–x, – y, – z ⁴;1+z, – 1+x, y ⁵;1+y, z, – 1+x.

2

a) Formation of monomeric iron β-diketiminate amide species Fe-4 and molecular structure of Fe-4 (CCDC 2211232). Ellipsoids are represented at 30% probability. Hydrogen atoms have been omitted, and the β-diketiminate substituents have been represented in wireframe view, for clarity; b) Formation of monomeric iron β-diketiminate amide species Fe-5 and the molecular structure of Fe-5 (CCDC 2211229). Ellipsoids are represented at 30% probability. Hydrogen atoms have been omitted and the β-diketiminate substituents have been represented in wireframe view, for clarity.

3

Synthesis of tetrameric iron β-diketiminate amide species Fe-6 and the molecular structure of Fe-6. Ellipsoids are represented at 30% probability. Hydrogen atoms have been omitted, and the β-diketiminate substituents have been represented in wireframe view, for clarity (CCDC 2211233).

4

Synthesis and Molecular structure of Fe-7. Ellipsoids are represented at 30% probability. Both solvent and hydrogen atoms have been omitted, and the β-diketiminate substituents have been represented in wireframe view, for clarity. Symmetry operations¹:1–x, 1–y, 1–z. (CCDC 2211234).

5

Synthesis and molecular structure of Fe-8 (CCDC 2211235). Ellipsoids are represented at 30% probability. Both solvent and hydrogen atoms have been omitted and the β-diketiminate substituents have been represented in wireframe view, for clarity.

6

Synthesis and molecular structure of Fe-9. Ellipsoids are represented at 30% probability. Hydrogen atoms have been omitted, and the β-diketiminate substituents have been represented in wireframe view, for clarity. (CCDC 2211236).

7

a) Synthesis of dimeric iron amide Fe-10 and molecular structure of Fe-10 (CCDC 2211228). Ellipsoids are represented at 30% probability. Both solvent and hydrogen atoms have been omitted and the β-diketiminate substituents have been represented in wireframe view, for clarity. Symmetry operations: ¹ x, 1/2–y, z; b) Synthesis of dimeric iron amide Fe-11 and one of the two independent molecules present in the structure of Fe-11 (CCDC 2211230). Ellipsoids are represented at 30% probability. Hydrogen atoms have been omitted and the β-diketiminate substituents have been represented in wireframe view, for clarity. Symmetry operations¹:1–x, 1–y, 1–z.

8

An overview of the coordination environment for different amide linkers tested. ^aDimer forms when Fe-2 is employed as the precursor.

9

a) The gross structure of Fe-3 (solvent omitted) viewed along the [001] direction and (b) the [111] direction, emphasizing the accessible channels in the array. Hydrogen atoms have been omitted and the β-diketiminate substituents have been represented in wireframe view, for clarity. c) Gross structure of Fe-6 (solvent omitted) viewed along the [010] direction showing the offset layers of molecules that stack along the b-axis. Hydrogen atoms have been omitted and the β-diketiminate substituents have been represented in wireframe view, for clarity. d) The gross structure of Fe-8 (solvent omitted) viewed along the [011] direction emphasizing the accessible channels in the array. Hydrogen atoms have been omitted and the β-diketiminate substituents have been represented in wireframe view, for clarity.

10

Isotherms showing the adsorption and desorption of N₂ gas by Fe-3 (●/○; purple closed and open circle),Fe-6 (●/○; yellow closed and open circle) and Fe-8 (●/○; turquoise closed and open circle). Analysis was undertaken at 77 K.