Solid state structures carboxylic acids

The solid state structure of (3>S,8 Sj-10-(8-amino-6-azaspiro[3,4]octan-6-yl)-9-fluoro-3-methyl-7-oxo-2,3-dihydro-7//-pyrido[l,2,3-dfe]-l,4-benzoxa-zine-6-carboxylic acid (218) was determined by X-ray diffraction study (98CPB1710). The structure of 6,10-dihydropyrido[2,l-c][l,4]benzoxazine-6,10-dione 219 was established by X-ray diffraction analysis. It contains a crystal solvate with /j-xylene (99MI40). 

The solid-state structure of (lS)-5,8,9-trihydroxy-2,3-dihydro-l/7-pyrimido-[l,2-a]quinoline-l-carboxylic acid pentahydrate was determined by X-ray investigations [91ZN(C)933. The structure of an iron(III)-containing pseudobactin, a siderophore containing a (lS)-5-amino-8,9-dihydroxy-2,3-dihydro-l//-pyrimido[l,2-a]quinazoline-l-carboxylic acid moiety (8), was determined by X-ray diffraction investigations (81 Mil). 

If two or more such carboxylic acid groups are present in a molecule, intricate solid-state structures may be assembled, as seen in the ribbon-like solid state structure of terephthalic acid (7.41). 

Figure 7-24. Self-complementary hydrogen bonding within a carboxylic acid allows the construction of intricate solid state structures, as seen in the crystal structure of terephthalic acid, 7.41 carbon atoms are grey, hydrogen atoms white and oxygen atoms black...

X-Ray crystallographic analysis used alongside solution phase techniques such as NMR, is invaluable in the design of selective anion receptors as it can be used to define the solid-state structure of the anion-bound complex. Several X-ray structures of anion-bound complexes of [Ln.la]3+ have been defined recently (acetate, lactate, citrate, alanine, glycine, methionine, serine and threonine) [8,21,22], The complexes adopt a monocapped square antiprismatic structure with one base comprising of four N atoms of the macrocycle and the other base containing three O atoms of the pendent arms. The latter base is completed by a carboxylate O donor of the anion, which binds in a bidentate manner and simultaneously caps this base by O (acetate), OH (a-hydroxy acids) or NH2 (a-amino acids). The nature of the donor atom in the capping (or axial) position correlates well with the observed NMR shift in the solution phase. 

Single crystal nmr spectra have been obtained for the resonance in K2Pt(CN)4Bro.3(H20)3, and the chemical shift tensor determined (565). The principal values (relative to the carboxyl carbon in acetic acid) have been reported as uu = 261 lOppm (parallel to the CN bond), <722 = — 48 10 ppm (perpendicular to the CN bond and Pt-Pt chain) and <733 = —10 5 ppm (parallel to the Pt-Pt chain). The primary effect on the chemical shift tensor of the cyanide bonding to the platinum and of the solid state structure is the nonzero asymmetry produced around the CN bond (565). 

The presence of hydrogen bonding has important effects on the solid state structures of many compounds, as we have already discussed for ice (Section 7.2) and carboxylic acids (Box 10.4). The solid state structures of some simple carboxylic acids are more complex than one might at first imagine. Figure 10.5c shows part of the solid state packing... 

---