A one-dimensional inorganic–organic hybrid compound: catena-poly[ethylenediammonium [indate(III)-di-μ-hydrogenphosphato(V)-μ-hydroxido] monohydrate]

The title compound, (C2H10N2)[In(HPO4)2(OH)]·H2O, was synthesized under hydrothermal conditions. The structure of this hybrid compound consists of isolated inorganic chains with composition ∞[In(HPO4)4/2(OH)2/2] running along [010]. The coordination of the InIII atom is distorted octahedral. The ethylenediammonium cation and the disordered water molecule (site-occupation factors = 0.7:0.3) ensure the cohesion of the structure via N—H⋯O and O—H⋯O hydrogen bonds.

Accordingly, in the past two decades, amine templated indium phosphates were in the focus of investigation, providing one-dimensional chain, two-dimensional layered and three-dimensonal open-framework structures with different In:P ratios (Chen et al. 2007;Thirumurugan & Srinivasan, 2003;Huang et al. 2010). In the present work, a new indium phosphate with a In:P ratio of 1:2, namely (H 3 NCH 2 CH 2 NH 3 )[In(HPO 4 ) 2 (OH)] . H 2 O was hydrothermally synthesized and structurally characterized.
The asymmetric unit of the title compound is drawn in Fig. 1. A three-dimensional polyhedral view of its crystal structure is represented in Fig. 2. It shows InO 4 (OH) 2 octahedra linked to PO 3 OH tetrahedra by sharing corners in the way to build ∞ [In(OH) 2/2 (HPO 4 ) 4/2 ] chains running along [010]. Fig. 3 shows the InO 6 octahedra linked to another via their hydroxide vertices, giving rise to a one-dimensional linear chain. Adjacent octahedra are additionally interconnected by PO 3 OH tetrahedra by sharing their terminal O atoms with four tetrahedra. A similar connectivity is observed in the structure of (C 4 N 2 H 12 )[In 2 (HPO 4 ) 2 (H 2 PO 4 ) 2 F 2 ] (Chen, Yi et al., 2006).
The +III and +V oxidation states of the In and P atoms were confirmed by bond valence sum calculations (Brown & Altermatt, 1985). The calculated values for the two In III+ and P V+ ions are as expected, viz. 3.25 and 5.04, respectively. The values of the bond valence sums calculated for all oxygen atoms are: 1.33 and 1.34 for the terminal O atoms O1 and O5, 2.29, 2.30 and 2.26 for O4, O8 and O9, respectively, and 1.82 for all other O atoms except that of the water molecule (O10) which amounts to 2.12. The difference between these values is explained by the nature and the length of the P-O bonds. From the two tetrahedrally coordinated phosphorus atoms P1 and P2, each shares two O atoms with adjacent indium atoms (average distance P-O = 1.520 Å) and possesses one terminal P1═O1 = 1.510 (2) Å, P2═O5 = 1.509 (2) Å and one P1-O4H = 1.579 (2) Å, P2-O8H = 1.577 (2) Å bond. The terminal O atoms are involved in strong hydrogen bonds (see below) which likewise explains their low bond valence sum. These results are in good agreement with the framework formula and are in close agreement with those reported in the literature for similar indium phosphates (Li et al. 2006;Du et al. 2004).
The ethylenediammonum cation and the water molecules ensure the cohesion of the structure via N-H···O and O-H···O hydrogen bonds (Fig. 1, Table 2).

Experimental
Single crystals of the title compound were hydrothermally synthesized from a reaction mixture of indium oxide (In 2 O 3 ; 0,388 g), phosphoric acid 85% wt (H 3 PO 4 ; 0,35 ml), ethylenediamine (NH 2 (CH 2 ) 2 NH 2 ; 0,3 ml) and water (H 2 O; 10 ml). In supplementary materials sup-2 addition, 40% wt fluoric acid (HF; 0,1 ml) was added to the mixture to provide fluoride ions which can act as a mineralizing agent in the hydrothermal synthesis and can play a structure-directing role. The hydrothermal reaction was conducted in a 23 ml Teflon-lined autoclave under autogeneous pressure at 398 K for two days. The resulting product was filtered off, washed with deionized water and was dried in air. It consisted of a yellow powder in addition to a few colorless parallelepipedic crystals of the title compound.

Refinement
All O-bound, N-bound and C-bound H atoms were initially located in a difference map and refined with O-H, N-H and C-H distance restraints of 0.82 (1) Å, 0.89 (1) Å and C-H 0.97 (1) Å, respectively. In a subsequent cycle they were refined in the riding model approximation with U iso (H) set to 1.5U eq (O) or (N) and U iso (H) set to 1.2 U eq (C). The refinement of the site occupancy of the O atoms of the water molecule shows full occupation. However, the electron density is distributed over two adjacent positions (O10 and O11). The refinement of the occupancy rates of these two positions led to a site occupancy factor of 0.7 for O10 and of 0.3 for O11, accompanied with considerable improvements in R and Rw factors.
From the synthetic conditions one might expect an incorporation of Fions. The distinction by X-ray diffraction between Fand O 2is difficult. However, when the relevant OH positions were replaced by F -, a small worsening of the reliability factors was observed. Moreover, the clearly discernible proton positions in the difference Fourier maps point to OH rather than to F. Nevertheless, the existence of a very small amount of Fincorporated in the structure cannot be excluded.

catena-poly[ethylenediammonium [indate(III)-di-µ-hydrogenphosphato(V)-µ-hydroxido] monohydrate]
Crystal data (C 2  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 > σ(F 2 ) is used only for calculating Rfactors(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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )