2′-Amino-3,6-dihydroxyxanthene-9-spiro-1′-isoindolin-3′-one monohydrate

The title compound, C20H14N2O4·H2O, was synthesized by the reaction of fluorescein and hydrazine hydrate in ethanol. In the crystal structure, the organic molecules are linked into extended two-dimensional networks by intermolecular hydrogen bonding. Additional face-to-face π–π stacking interactions between the phenolic benzene rings in two adjacent molecules [centroid-to-centroid separation = 3.773 (3) Å] link the molecules into a three-dimensional framework.


Comment
The development of fluorescent probes for determining various analytes with high selectivity and sensitivity has attracted much attention in recent years (Chen, et al., 2006). So, an enormous amount of research has gone into the design and synthesis of fluorescent probes. Fluoresein is one of the most popular dyes, because fluorescein has many advantages, including high fluorescence quantum efficiency, high extinction coefficient around 490 nm, and high water solubility under physiological conditions, therefore, it is usually utilized as reporting group in routine optical analysis (Yang et al., 2005;Adamczyk et al., 2000). For example, The title compound can be a probe to detect copper(II), cobalt(II) and hydrogen peroxide. This promoted us to attempt to prepare and obtain the crystals of the other fluorescein derivatives and characterized their crystal structures. In the title compound, C 20 H 14 N 2 O 4 ·H 2 O, termed "fluorescein hydrazide", was prepared by reaction of fluorescein with hydrazine hydrate. Although fluorescein hydrazide has been reported by others, there is no report about the crystal of fluorescein hydrazide suitable for single-crystal X-ray diffraction. Herein, we report the crystal structural details on fluorescein hydrazide.
The fluorescein hydrazide was confirmed to have a five-membered spirolactam structure. The spiro form fluorescein hydrazide bearing a cleavable active bond is characterized by single-crystal X-ray diffraction.
The asymmetric unit contains one organic molecule and one water molecule. The benzene ring of phenol deviates only slightly from planarity with a dihedral angle of 10.18 (3)°. The water O atom acts as a hydrogen bond acceptor and donor from the hydroxy group in a neighouring organic molecule, thereby forming extended 2-D networks (Table1, Fig.2). The crystal packing is characterized by π···π stacking interactions. The molecules are stacked in an antiparalled fashion, with phenyl ring of phenol centroid-centroid separation of 3.773 (3) Å. Together with the hydrogen bonds, these interactions lead to a three-dimensional supramolecular network pattern (Fig. 2).

Experimental
For the synthesis of fluorescein hydrazide, different procedures have been reported (Orndorff et al., 1927). In this work, a modified literature procedure was used to produce fluorescein hydrazide. A solution of fluorescein (1.0 g, 3.0 mmol) in absolute ethanol (50 ml) was stirred and 4.0 ml (excess) hydrazine hydrate (85%) was then added dropwise with vigorous stirring over 5 minutes. The solution was refluxed for 5 h. The reaction mixture was cooled and the solvent was removed under reduced pressure to give dark orange oil. Then, 30 ml of ethanol/water (v:v = 7:3) was added to the oil, a light orange crystal suitable for single-crystal X-ray diffraction was obtained by evaporating the resulting solution in air for several days. The resulting light orange crystal was filtered, washed with ethanol, and then dried in vacuo, affording of the title compound [yield: 0.98 g, 90%]. The product is stable in air.
supplementary materials sup-2 Refinement All H atoms were positioned geometrically (C-H = 0.93 Å and O-H = 0.82 Å), and refined using a riding model, with U iso (H) = 1.2U eq (C or O). Fig. 1. The asymmetric unit, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. 2'-Amino-3,6-dihydroxyxanthene-9-spiro-1'-isoindolin-3'-one monohydrate  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.