- Novel ternary graphite intercalation compounds (GICs) of alkali metal cations
and a wide variety of amines have been synthesized by one-pot chemical syntheses.
Alkali metals studied includes Li, Na and K. The families of amines employed are nalkylamines,
branched alkylamines, and different structural isomers of diamines and
polyamines. Intragallery structures of the amine co-intercalates residing between the
graphene sheets are proposed based on powder X-ray diffraction (PXRD),
supplemented by compositional analyses, thermal analyses, and structure optimization
A homologous series of M-n-alkylamine-GICs (M = Na, Li) is reported for the
first time, with the n-alkylamines of 3-14 carbon atoms (nC3-nC14). The following
new GICs with indicated stages and intercalate arrangements are obtained: stage 1, d[subscript i] ~
0.70 nm, monolayer (nC3, nC4); stage 1, d[subscript i]~ 1.10 nm, bilayer (nC6, nC8); and stage
2, d[subscript i] ~ 1.10 nm, bilayer (nC12, nC14). Here d[subscript i] is the gallery height. Two features new
to donor-type GICs found are (i) an intercalate bilayer arrangement with guest alkyl
chains parallel to encasing graphene layers, and (ii) the transition from an intercalate
bilayer to monolayer arrangement upon evacuation for nC6.
GICs containing branched alkylamines co-intercalates are prepared and their
intragallery structures compared to those of selected n-alkylamines. A notable
difference is observed for amines with 4 carbon atoms. While the linear n-butylamine
forms parallel monolayers (d[subscript i] ~ 0.70 nm), the branched analogs (iso-butylamine and
sec-butylamine) instead form bilayers with d[subscript i] ~ 1.30 nm. This result contrasts with the
general observation that more sterically-hindered intercalates tend to intercalate at
lower concentrations. This structural difference is not observed, however, between npropylamine
and iso-propylamine (d[subscript i] ~ 0.70 and 0.76 nm respectively).
A rare example of a ternary GIC exhibiting cation-directed orientation of the
diamine co-intercalate (1,2-diaminopropane, 12DAP) is reported. Depending on the
cation M⁺, this diamine can exhibit either perpendicular (M = Li, d[subscript i] ~ 0.81 nm),
parallel (M = K, d[subscript i] ~ 0.70 nm) or a tilted orientation (M = Na, d[subscript i] ~ 0.75 nm).
Interestingly, the gallery expansions increase as the cationic radii decrease.
The structural effect of the diamines is systematically investigated, employing
diamines with different alkyl chain lengths, different positions of an –NH₂ group, and
different –CH₃ substituent patterns. The first example of a monolayer perpendicularto-
parallel transition in a GIC is reported for Li- ethylenediamine (EN)-GIC, with the
respective change in d[subscript i] from 0.85 to 0.68 nm. The sodium analog, Na-EN-GIC, is also
prepared and described. We also report quaternary compounds of mixed cations
(Li,Na)-12DAP-GIC and mixed amines Na-(EN,12DAP)-GIC.
Ternary graphite intercalation compounds (GICs) of alkali metals and
polyamines are prepared. Structural modifications similar to the diamines indicated
above are also observed for polyamine intercalates. The polyamines studied include
diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N,N,N',N',N'-
pentamethyldiethylenetriamine, and tris(2-aminoethyl)amine. Most of the new GICs
have amine intercalates in parallel orientation (d[subscript i] ~ 0.76-0.86 nm for monolayers, and
1.13 nm for bilayers), though the GIC stage numbers depend on the size of the
polyamine. In contrast, the star-shaped polyamine tris(2-aminoethyl)amine shows a
perpendicular monolayer orientation with d[subscript i] ~ 1.06 nm.