Hybrid cubic/hexagonal diamondoids

Abstract

Novel compounds having a hybrid cubic/hexagonal diamond crystal structure are disclosed. Each of the four compounds have the stoichiometric formula C26H32 and a molecular weight of 344. The four compounds are contemplated to have a utility in diamond film nucleation.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention are directed to novel compounds comprising hybrid cubic/hexagonal diamondoids. More specifically, embodiments of the present invention are directed to four compounds, each of which exhibit both the cubic diamond structure and the hexagonal diamond structure.

2. State of the Art

There are two forms of the diamond crystal structure, one hexagonal, the other cubic. As discussed in Carbon Molecules and Materials, edited by R. Setton, P. Bernier, and S. Lefrant (Taylor and Francis Inc., London and New York, 2002), a new phase of carbon, the hexagonal phase, was found among the crystals of cubic diamond in an x-ray diffraction experiment of synthetic diamond carried out at pressures greater than 130 GPa. According to Setton et al., the hexagonal phase may be obtained from pyrocarbons that have been subjected to a compression perpendicular to the layers, followed by annealing at a temperature greater than 1300 K. Hexagonal diamond has the lattice cell parameters a_hexagonal=2.52 Å=a_cubic/√2, =4.12 Å=2c_cubic/√3, and a P6₃/mmc space group. The density of hexagonal diamond is 3.51 g/cm3, which is the same as that in cubical diamond, and the position of the carbons is the same as the atomic positions in the wurtzite crystal structure. A hexagonal diamond crystal cage is shown in FIG. 1A, where only the carbon atom lattice sites have been shown (at the line intersections), and the hydrogen atoms have been omitted.

Also discussed in Carbon Molecules and Materials are the properties of cubic diamond. Cubic diamond has a space group of Fd3m, with the latice cell parameters a_cubic=b_cubic=c_cubic=3.5597 angstroms. Cubic diamond has 8 atoms per unit cell, and a density of 3.51 g/cm³. The carbon atoms of cubic diamond are all in the chair conformation, as illustrated in FIG. 1B, where again, only the carbon atom lattice sites have been shown.

Cubic diamondoids are known in the art. What has not been disclosed are diamondoids that contain both the cubic and hexagonal forms of the diamond crystal structure. Each of the four hybrid cubic/hexagonal compounds of the present invention have the stoichiometric formula C₂₆H₃₂ and a molecular weight of 344.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to novel compounds comprising hybrid cubic/hexagonal diamondoids. More specifically, embodiments of the present invention are directed to four compounds, each of which exhibit both the cubic diamond structure and the hexagonal diamond structure.

It is contemplated that a utility of the present cubic/hexagonal hybrid diamondoids is the nucleation of diamond films.

The combination of boat and chair configurations of the cage faces of the diamond structure of the present embodiments are contemplated to facilitate the nucleation of a diamond film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate cage structures that are a part of the hexagonal and cubic diamond crystal structures, respectively;

FIG. 2A illustrates the hexagonal diamond crystal cage unit of the first two 344 molecular weight hybrid molecules;

FIG. 2B illustrates the hexagonal diamond crystal cage unit of the second two 344 molecular weight hybrid molecules;

FIG. 3A shows a perspective structure of the first 344 molecular weight hexagonal-cubic hybrid compound;

FIG. 4A shows a perspective structure of the second 344 molecular weight hexagonal-cubic hybrid compound;

FIG. 5A shows a perspective structure of the third 344 molecular weight hexagonal-cubic hybrid compound;

FIG. 6A shows a perspective structure of the fourth 344 molecular weight hexagonal-cubic hybrid compound;

FIGS. 3B-D illustrate side, end, and top views of the first 344 molecular weight hybrid structure;

FIGS. 4B-D illustrate side, end, and top views of the second 344 molecular weight hybrid structure;

FIGS. 5B-D illustrate side, end, and top views of the third 344 molecular weight hybrid structure;

FIGS. 6B-D illustrate side, end, and top views of the fourth 344 molecular weight hybrid structure; and

FIG. 7 shows an exemplary method by which the hybrid cubic/hexagonal diamondoids of the present invention may be isolated.

DETAILED DESCRIPTION OF THE INVENTION

Structures

The four compounds of the present invention have a molecular weight of 344, and are fully saturated polycyclic hydrocarbons that contain a mixture of hexagonal and cubic diamond crystal structures. The hexagonal portion of these four 344 molecular weight, C₂₆H₃₂ hybrid compounds consist of the two basic hexagonal dimer units, shown individually in FIGS. 2A and 2B, respectively.

In the case of the FIG. 2A hexagonal dimer unit, only two faces (21 and 22) are available for the attachment of the cubic units. Shown in FIG. 2A is the hexagonal diamond crystal dimer cage unit contained in 344 hybrid compounds depicted in FIGS. 3 and 4. Reference numerals 21 and 22 in FIG. 2A point to the two hexagonal cage faces where cubic cages can potentially face-fuse in order to generate the FIG. 3 and FIG. 4 structures. To generate the compound in FIG. 3, a first cubic cage attaches (face fuses) to the cage face 21, and a second cubic cage attaches (face fuses) to the cage face 22. In an alternate way of attaching two cubic cages to the structure shown in FIG. 2A, thus generating the compound in FIG. 4, a first cubic cage attaches (face fuses) to the cage face 21 (as before), but the second cubic cage attaches to the first cubic cage already attached, instead of attaching to hexagonal face 22. This second hexagonal face 22 remains open.

The hexagonal cage dimer shown in FIG. 2A is symmetrical such that the attachment of a single cubic diamond crystal cage to either face 21, 22 generates identical structures. To create the second of the two hybrids from FIG. 2A, the second cubic diamond must be face-fused to one of the three available cubic cage faces. Again, due to the high symmetry, attachment of the second cubic cage to any of the three available cubic faces produces identical structures.

Shown in FIG. 2B is the hexagonal diamond crystal dimer cage unit contained in 344 hybrid compounds depicted in FIGS. 5 and 6. Similar to the situation for FIG. 2A, the FIG. 2B hexagonal cage dimer has only two cage faces 23, 24 available for the attachment of a cubic unit. The third 344 molecular weight hybrid contains this hexagonal dimer unit with a cubic diamond crystal cage attached to each of the two available hexagonal faces 23, 24, thus generating the structure shown in FIG. 5A. Because the hexagonal dimer shown in FIG. 2B is symmetrical, attaching cubic cages to the faces 23, 24 in either order generates identical structures.

The fourth 344 molecular weight hybrid that may be generated from the hexagonal dimer of FIG. 2B is shown in FIG. 6A. In this case, the second cubic cage is face-fused to one of the faces of the first (already attached) cubic cage. Again, due to the high symmetry of the FIG. 2B hexagonal dimer with a cubic cage attached to either face 23, 24, attachment of a cubic cage to any of the three available faces of the first attached cubic face produces identical faces.

In an alternative description of the various embodiments, the number of faces that correspond to a particular type of cage contained within each hybrid may be tabulated. For example, the hybrid depicted in FIG. 3 contains two four-faced cages and two five-faced cages. This is the same situation for the hybrid depicted in FIG. 4. The hybrid depicted in FIG. 5 contains two four faced cages, one five-faced cage, and three three-faced cages. The hybrid molecule described in FIG. 6 may be described in the same manner. See Table 1:

TABLE 1
Number of x-faced cages in each of the hybrid molecules
	hybrid	number cages	number cages	number cages
	molecule	with 4 faces	with 5 faces	with 3 faces
	FIG. 3	2	2	0
	FIG. 4	2	2	0
	FIG. 5	2	1	3
	FIG. 6	2	1	3

Another way in which the four 344 molecular weight hybrid molecules may be described is by tabulating whether or not the cages in each of the hybrids are in the chair or boat conformations, regardless of whether they are positioned in the 4-, 3-, or 5-faced cages. Again, the 4-faced cages are part of the cubic diamond structure, and the 3-faced and 5-faced structures are a part of the hexagonal diamondoid structure. This information may be seen in Table 2:

TABLE 2
Number of cages in the chair or boat configuration
	Cubic	Hexagonal	Hexagonal
	Number of	4	3	5
	faces per cage
	unit
	Types of faces	All 4 are chair	All 3 are boat	3 are boat;
				2 are chair

Another way in which the four 344 molecular weight hybrid molecules may be described is by tabulating the number of secondary, tertiary, or quaternary carbons in each molecule. Each of the four hybrid molecules has the stoichiometric formula C₂₆H₃₂, and for the 26 carbons of each molecule the number of secondary, tertiary, or quaternary carbons varies, as seen in Table 3:

TABLE 3
Number secondary, tertiary, and quaternary carbons
	hybrid	secondary	tertiary	quaternary
	molecule	carbons	carbons	carbons
	FIG. 3	6	20	0
	FIG. 4	7	18	1
	FIG. 5	12	8	6
	FIG. 6	10	12	4

Having described the four members of the 344 molecular weight hybrid cubic hexagonal structures in several different ways, this disclosure will now turn to methods of isolation.

Isolation

Petroleum feedstocks must be compared and selected prior to isolation of hexagonal-cubic hybrid diamondoids. Once a feedstock has been selected, a GCMS assay for the 344 MW hexagonal-cubic hybrid diamondoids must be developed which identifies the molecular ion and gas chromatographic retention times. Referring to FIG. 7, the initial isolation step involves distillation to concentrate target species followed using the assay. Distillate fractions are then pyrolyzed or hydroprocessed to remove nondiamondoid hydrocarbons.

Remaining aromatic and polar compounds can be removed from pyrolysates by liquid chromatography and hexagonal-cubic hybrid diamondoids can be isolated either by preparative gas chromatography and/or high performance liquid chromatography (HPLC). Once isolated and crystallized, structures may be identified by x-ray diffraction.

It is contemplated that a utility of the present cubic/hexagonal hybrid diamondoids is the nucleation of diamond films.

The combination of boat and chair configurations of the cage faces of the diamond structure of the present embodiments are contemplated to facilitate the nucleation of a diamond film.

Many modifications of the exemplary embodiments of the invention disclosed above will readily occur to those skilled in the art. Accordingly, the invention is to be construed as including all structure and methods that fall within the scope of the appended claims.

Claims

1. A composition of isolated hybrid cubic/hexagonal diamondoids comprising an isolated hybrid cubic/hexagonal diamondoid having the following structure:

2. A composition of isolated hybrid cubic/hexagonal diamondoids comprising an isolated hybrid cubic/hexagonal diamondoid having the following structure:

3. A composition of isolated hybrid cubic/hexagonal diamondoids comprising an isolated hybrid cubic/hexagonal diamondoid having the following structure:

4. A composition of isolated hybrid cubic/hexagonal diamondoids comprising an isolated hybrid cubic/hexagonal diamondoid having the following structure:

5. A method of nucleating a diamond film, wherein the film is nucleated by the composition of claim 1.

6. A method of nucleating a diamond film, wherein the film is nucleated by the composition of claim 2.

7. A method of nucleating a diamond film, wherein the film is nucleated by the composition of claim 3.

8. A method of nucleating a diamond film, wherein the film is nucleated by the composition of claim 4.

9. A diamond film produced by the method of claim 5.

10. A diamond film produced by the method of claim 6.

11. A diamond film produced by the method of claim 7.

12. A diamond film produced by the method of claim 8.