Linking Hydrogen Dicarboxylate Synthons with Substituted Guanidinium Cations: Transforming Rings and Chains into Two- and Three-Dimensional Structures

Hydrogen-bonding interactions between N,N‘,N‘ ‘-trisubstituted guanidinium cations and hydrogen dicarboxylates are
explored. The extended structures of these compounds combine established structural motifs for the hydrogen carboxylate anions
with C3-symmetric guanidinium links. Both N,N‘,N‘ ‘-triisopropylguanidine (TPG) and N,N‘-diisopropyl-N‘ ‘-pentafluorophenylguanidine
(DPArG) react in 1:1 stoichiometry with oxalic acid to yield compounds that were crystallized from tetrahydrofuran (THF) to give
(TPGH)(C2O4H)(THF)0.5(1) and (DPArGH)C2O4H(THF) (2). Compound 1 displayed hydrogen oxalate dimers (

(10) motif) that
are bridged with the TPGH+ cation to yield an open three-dimensional (3-D) structure that crystallized around occluded THF. In the
case of compound 2, the targeted (DPArGH)(C2O4H) incorporated an additional hydrogen-bonded THF molecule to provide a structure
in which the -O2CCOOH anion exhibited head-to-tail chains (C(5) motif) that are cross-linked through hydrogen bonds with
[(DPArGH)(THF)]+ to yield two-dimensional (2-D) layers that stack along the c-axis. TPG also reacts stoichiometrically with succinic
(butanedioic) acid and maleic (cis-2-butenedioic) acid to produce guanidinium hydrogen dicarboxylate salts (TPGH+)(-O2CC2H4CO2H)
(3) and (TPGH+)(-O2CCHCHCO2H) (4). The primary structure of 3 combines head-to-tail hydrogen-bonded chains of monoanionic
dicarboxylic acids with chain-spanning planar TPGH+ cations to give a cross-linked ladder motif that ultimately generates a 3-D
net. In the case of 4, the hydrogen maleate anion displayed a characteristic intramolecular, low barrier hydrogen bond (LBHB) (S(7)
motif). Hydrogen bonding between planar TPGH+ and the cyclic, planar anion leads to a layered solid-state structure consisting of
a corrugated 2-D net constructed from 16- and 42-membered rings.