(Butane-1,2,3,4-tetraol-κ3 O 1,O 2,O 3)(ethanol-κO)tris(nitrato-κ2 O,O′)erbium(III)

In the title ErIII–erythritol complex, [Er(NO3)3(C2H5OH)(C4H10O4)], the ErIII cation is chelated by one erythritol molecule, three nitrate anions and an ethanol molecule, completing an irregular ErO10 coordination geometry. The Er—O bond lengths are in the range 2.348 (3)–2.583 (3) Å. In the crystal, extensive O—H⋯O hydrogen bonding links the molecules into a three-dimensional supramolecular structure.

In the title Er III -erythritol complex, [Er(NO 3 ) 3 (C 2 H 5 OH)-(C 4 H 10 O 4 )], the Er III cation is chelated by one erythritol molecule, three nitrate anions and an ethanol molecule, completing an irregular ErO 10 coordination geometry. The Er-O bond lengths are in the range 2.348 (3)-2.583 (3) Å . In the crystal, extensive O-HÁ Á ÁO hydrogen bonding links the molecules into a three-dimensional supramolecular structure.
Data collection: CrystalClear (Rigaku, 2007); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL. Sugar-metal interaction is involved in many important biological processes (Gyurcsik & Nagy, 2000). Erythritol was used as a model compound to study the coordination behavior of hydroxyl groups of carbohydrate to metal ions.
The crystal structure of the title complex denoted as ErEN, where E stands for erythritol and N stands for nitrate) is shown in Fig. 1. This is isostructural with the Ho III compex (Hua et al., 2013). Three hydroxyl groups from one erythritol molecule, one hydroxyl group from ethanol, and six oxygen atoms from three bidentate nitrate ions are coordinated to Er(III), making the coordination number 10. Erythritol molecule is an O1, O2, O3-three hydroxyl group donor here.
The structure of ErEN is similar to NdEN, EuEN, YEN, GdEN and TbEN (Yang et al., 2003(Yang et al., , 2004(Yang et al., , 2012. Er-O distances range from 2.348 to 2.583′ Å, the average Er-O distance is 2.419Å. The structure of erythritol changed somewhat in the complex. The C-C bond length is 1.51Å and the C-O bond lengths are 1.39 and 1.47Å for a free erythritol (Bekoe & Powell, 1959). After coordination, the C-C bond lengths are 1.505 and 1.512Å and the C-O bond lengths are 1.422, 1.451, 1.445 and 1.456Å in ErEN. The C-C-C bond angle is 113° and the O-C-C bond angle is 107° for erythritol (Bekoe & Powell, 1959). After coordination, the C-C-C bond angles are 116.3 and 113.0° and the O-C-C bond angles range from 103.6 to 111.7° in ErEN. In addition, the torsion angle of C-C-C-C is 180° for erythritol. After coordination, the torsion angle of C-C-C-C is -57.2 (4)° in ErEN. The variation of the C-C-C-C torsion angle indicates the coordination to Er 3+ brings about significant variation of the conformation of erythritol.
The hydrogen bond networks in ErEN are formed by O-H···O hydrogen bonds between coordinated and uncoordinated hydroxyl groups of erythritol, ethanol and nitrate ions.

Experimental
Er(NO 3 ) 3 .6H 2 O and Erythritol were purchased from Shanghai Aladdin Chemical Reagents Company and was used without further purification. The procedure for the preparation of the title compound is as follows: Er(NO 3 ) 3 .6H 2 O (3 mmol) and erythritol (3 mmol) were dissolved in 6ml water and 6 ml ethanol. The solution was put on a water bath, and the temperature was raised to 353 K. Small aliquots of EtOH were periodically added to the solution during the heating process to prolong the reaction time. The resulting mixtures were filtered and left for crystallization in room temperature, the suitable crystals for X-ray diffraction measurements were obtained in two weeks.

Refinement
The C-bound H-atoms were placed in calculated positions (C-H 0.930 Å) and were included in the refinement in the riding model approximation, U iso (H) = 1.2U eq (C). The O-bound H atoms were located in a difference Fourier map and were refined with distance restraint of O-H = 0.84 Å, U iso (H) = 1.2U eq (O).

Figure 1
The crystal structure of the title complex, displacement ellipsoids drawn at 30% probability level. The Hydrogen atoms have been omitted for clarity.

\ (Butane-1,2,3,4-tetraol-κ 3 O 1 ,O 2 ,O 3 )(ethanol-\ κO)tris(nitrato-κ 2 O,O′)erbium(III)
Crystal data [Er(NO 3  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 1.46 e Å −3 Δρ min = −0.62 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. 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.