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Hydrogen Bonding Motifs of N,N‘,N‘ ‘-Trisubstituted Guanidinium Cations with Spherical and Rodlike Monoanions:  Syntheses and Structures of I-, I3-, and SCN- Salts

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posted on 04.01.2006, 00:00 by Farouq F. Said, Patrick Bazinet, Tiow-Gan Ong, Glenn P. A. Yap, Darrin S. Richeson
The trisubstituted guanidines N,N‘,N‘ ‘-triisopropylguanidine (TPG) and N,N-diisopropyl-N‘ ‘-2,6-dimethylphenylguanidine (DPArG) react with ammonium iodide in water to produce the iodide salts (TPGHNH3)I (1) and (DPArGH)I (2). Compound 1 displayed a complex cation that consisted of a 1:1 ratio of TPG and ammonium cation, and the solid-state structure of this compound is a three-dimensional hydrogen-bonded network in which all three guanidine nitrogens are involved in hydrogen bonding with a three-coordinate iodide anion. The orientation of the N-substituents of the cation in 2 led to hydrogen-bonded cation/anion chains. Triiodide salts, TPGH+I3- (3) and DPArGH+I3- (4), are also reported. The primary structures of 3 and 4 consist of hydrogen-bonded dimers. The shortest NH···I interactions for 3 are with one terminal and the central I atoms, while in 4 the two hydrogen-bonding interactions are to the terminal I centers. A third, slightly longer NH···I interaction in 3 led to an extended double layer chain structure. In 4, an NH interaction with the aromatic ring of an adjacent dimeric unit generated chains of dimers. The reaction between TPG and NH4SCN produced TPGH+SCN- (5) with a structure displaying two cystallographically unique cations, each with three hydrogen bonds to the thiocyanate anions. Two structural subunits were identified, a dimeric (TPGH+SCN-)2 unit and a cation/anion chain, and these are cross-linked via hydrogen-bonding interactions to yield the 3-D structure for 5.