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

In the title HoIII–erythritol complex, [Ho(NO3)3(C4H10O4)(C2H5OH)], the HoIII cation is chelated by a tridentate erythritol ligand and three bidentate nitrate anions. An ethanol molecule further coordinates the HoIII cation, completing the irregular O10 coordination geometry. In the crystal, an extensive O—H⋯O hydrogen-bond network links the molecules into a three-dimensional supramolecular structure.

In the title Ho III -erythritol complex, [Ho(NO 3 ) 3 (C 4 H 10 O 4 )-(C 2 H 5 OH)], the Ho III cation is chelated by a tridentate erythritol ligand and three bidentate nitrate anions. An ethanol molecule further coordinates the Ho III cation, completing the irregular O 10 coordination geometry. In the crystal, an extensive O-HÁ Á ÁO hydrogen-bond network 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.  The interaction between carbohydrates and metal ions is of increasing interest as it occurs in many important biological processes (Gyurcsik & Nagy, 2000). Erythritol is a model compound to study the coordination behavior of hydroxyl groups to metal ions. For lanthanide nitrate-erythritol complexes, two kinds of metal complexes were observed: coordinate complex with water and coordinate complex without water (Yang et al., 2003(Yang et al., , 2004(Yang et al., , 2012. The title holmium nitrate-erythritol complex is belonging to the complexes without water.
The title complex denoted as HoEN, where E stands for erythritol and N stands for nitrate, which is shown in Fig. 1.

Experimental
Ho(NO 3 ) 3 .6H 2 O (3 mmol) and erythritol (3 mmol) were dissolved in 6 ml 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 = 0.93 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 restranits of O-H = 0.84 Å, U iso (H) = 1.2U eq (O).

,O 3 )(ethanol-κO)tris(nitrato-κ 2 O,O′)holmium(III)
Crystal data [Ho(NO 3  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.11 e Å −3 Δρ min = −0.83 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.