Crystal structure of an organic–inorganic hybrid compound based on morpholinium cations and a β-type Anderson polyanion

The crystal structure of the novel organic–inorganic hybrid compound is based on a β-type Anderson polyoxidomolybdate anion containing a central FeIII ion. In the crystal, intermolecular N—H⋯O and O—H⋯O hydrogen bonds link the components into a three-dimensional network structure.


Chemical context
Polyoxidometalates (POM) are attractive molecular building blocks used in the formation of multidimensional organicinorganic hybrid networks during self-organization processes (Pope & Mü ller, 2001;Mü ller et al., 1998;Long et al., 2007). POMs play an important role in the design of new classes of functionalized materials not only because of their topological versatility and high dimensional architectures, but also due to their rich diversity of remarkable properties. Several related compounds with Anderson-type polyoxidometalate anions and organic cations, such as (C 4 H 12 N 2 ) 5 [Al(OH) 6 Mo 6 O 18 ] 2 -(SO 4 ) 2 Á16H 2 O (Yang et al., 2009), (C 4 H 10 NO) 3 [Cr(OH) 6 -Mo 6 O 18 ]Á4H 2 O (Yang et al., 2011), (C 6 H 10 N 3 O 2 ) 2 Na(H 2 O) 2 -[Al(OH) 6 Mo 6 O 18 ]Á6H 2 O (Thabet et al., 2012) and other compounds with an Fe III central ion (Marcoux et al., 2003;Allain et al., 2008;Dessapt et al., 2011) have been reported. In -type Anderson polyoxidoanions, which are characterized by a planar arrangement of the metal atoms, each Mo VI atom has two terminal oxygen atoms, two bridging O atoms and two bridging OH functions which make it highly reactive and easily coordinated by varieties of transition metal atoms in the anion. ISSN 2056-9890 Here we report synthesis and structure of the new organicinorganic hybrid compound (C 4 H 10 NO) 5 [Fe III (OH) 6 Mo 6 O 18 ]-(SO 4 )Á3.5H 2 O, (I).

Structural commentary
The asymmetric unit of compound (I) is made up of one Anderson -type polyoxidoanion, [Fe(OH) 6 Mo 6 O 18 ] 3À , abbreviated in the following as {FeMo 6 }, five morpholinium cations (C 4 H 10 NO) + , one sulfate anion and four non-coordinating water molecules (Fig. 1). Three of the morpholinium cations are disordered over two sets of sites and one water molecule (O1W) shows half-occupancy. The {FeMo 6 } anion is formed by six edge-sharing [MoO 6 ] octahedra, which are arranged hexagonally around the central [Fe(OH) 6 ] octahedron with bond lengths and angles that are within the expected ranges for this type of POM anion (Cao et al., 2007). The six hydroxyl groups of the Anderson-type polyoxoanion are involved as donor groups in hydrogen-bond formation with O atoms of the sulfate anions and the non-coordinating water molecules.

Figure 2
The crystal packing of compound (

Synthesis and crystallization
The title compound was synthesized by the following procedure: 0.320 g (0.8 mmol) of iron(III) sulfate was dissolved in 10 ml of double-distilled water. To this solution 4 ml (5 mmol) of morpholine and 0.309 g (1.5 mmol) of Na 2 MoO 4 were added during constant stirring. By the addition of 30% wt sulfuric acid, the pH was adjusted to 2.5. The resultant solution was filtered and the filtrate kept at room temperature. After few weeks, light-brown crystals were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Three of the five crystallographically independent morpholinium cations are disordered, for which all atoms are distributed between two positions. The refined site occupation factor ratios are as follows: 0.857 (6):0.143 (6), 0.703 (9):0.297 (9) and 0.857 (6): 0.143 (6) for O1C-C6C/O11C-C61C, O1D-C6D/O11D-C61D and O1E-C6E/O11E-C61E, respectively. All non-hydrogen atoms were refined anisotropically, except for the minor parts of the disordered morpholinium cations. The positions of the H atoms were initially located in difference Fourier maps. All H atoms were fixed at ideal positions, with U iso (H) = 1.2U eq of the parent atom (1.5U eq for water H atoms). In the final refinement cycles, H atoms of the O1W water molecule were allowed to ride on the parent O atom (AFIX 3 in SHELXL2014; Sheldrick, 2015), H atoms of the other water molecules were fixed with the AFIX 6 instruction. For the minor component of disorder for morpholinium cation (O11C > C61C) the SAME instruction was used. Pairs of morpholinium cations (labelled C and E) were initially refined with individual occupation factor variables which turned out to refine to the same value (taking into account standard uncertainties). As a result of the fact that disordered parts of these two cations are connected by hydrogen-bonding interactions, disorder was restrained with a common occupation factor variable in the final refinement. One of the O atom of a water molecule (O1W) is characterized by a significantly elongated displacement parameter. The occupation factor of this molecule was arbitrarily fixed at 50%.