YCu(TeO3)2(NO3)(H2O)3: a novel layered tellurite

A new layered tellurite has been synthesized, where the structural unit consists of [Cu2(TeO3)4]4− loop-branched chains of {Cu⋯Te⋯Cu⋯Te} squares, which are linked further into layers only through Y(O,H2O)8 polyhedra.


Chemical context
Recent discoveries of a wide range of novel tellurium minerals have prompted numerous structural studies of tellurium oxysalts (Kampf et al., 2013;Christy et al., 2016a). As well as the characterization of these naturally occurring minerals, various syntheses have also been undertaken as part of this ongoing study, yielding an array of new structures, including that of novel Na 11 H[Te(OH) 3 ] 8 [SO 4 ] 10 (H 2 O) 13 (Mills et al., 2016). Several tellurium oxide species with various yttrium oxide polyhedra present in the structure have been synthesized in the past, including compounds with both Te IV and Te VI atoms. Tellurium is stable in numerous oxidation states and shows large diversity in bonding . Its +IV and +VI oxidation states are of greatest interest in relation to naturally occurring weathering products of minerals, and are able to form a wide variety of oxide polyhedra, with TeO 3 2À most prevalent (Song et al., 2014). The TeO 3 2À anion shows a wide variety of connectivities, with three oxido ligands and the 5s 2 electron lone pair occupying the vertices of the distorted polyhedra, and are found in a variety of layer and chain structures in inorganic compounds (Johansson & Lindqvist, 1978). This is demonstrated in compounds such as NaYTe 4 O 10 with YO 8 and TeO 4 polyhedra, KY(TeO 3 ) 2 and RbY(TeO 3 ) 2 with YO 6 octahedra and trigonal-pyramidal TeO 3 2À anions, CsYTe 3 O 8 with YO 6 and TeO 4 polyhedra (Kim et al., 2014), as well as yttrium tellurium oxides with Te VI atoms (Kasper, 1969;Hö ss & Schleid, 2007;Noguera et al., 2012). As a consequence of this range of chemistry, tellurium is the most anomalously diverse element found in minerals ISSN 2056-9890 compared to its scarcity in the earth's crust (Christy, 2015). Many copper-containing tellurium oxides have been successfully synthesized (Feger et al., 1999;Koteswararao et al., 2013;Sedello & Mü ller-Buschbaum, 1996), and copper is also present in many tellurium-containing minerals; indeed, out of the unusually large inventory of tellurium secondary minerals at Otto Mountain, the majority contains copper (Christy et al., 2016a). Despite this, there are very few synthetic rare earth copper tellurium oxides known, and to the best of our knowledge a compound containing all three of copper, yttrium and tellurium has not been characterized so far. Although layered structures with interstitial ions are common for Te IV compounds, nitrate is found as an anion in very few, which motivates the use of metal nitrates in the synthesis of novel tellurium oxides. The only other compounds with simple tellurite and nitrate anions whose structures have been reported to date are the layered compounds Ca 6 (TeO 3 ) 5 (NO 3 ) 2 and Ca 5 (TeO 3 ) 4 (NO 3 ) 2 (H 2 O) 2 (Stö ger & Weil, 2013). Nitrates of polymerized Te(IV) complexes are also known. The compound AgTeO 2 (NO 3 ) (Olsson et al., 1988) contains an electrically neutral [Te 2 O 4 ] 0 chain (Christy et al., 2016b) (Anderson et al., 1980;Christy et al., 2016b).

Structural commentary
Bond-valence sums are given in Table 1. In general, the bondvalence data of Table 1 were calculated using the bondvalence parameters of Brown & Altermatt (1985), except that the Te-O data were from . However, Brown (2009) noted that no single pair of r 0 and b values is adequate for O-H bonds, since OÁ Á ÁO repulsion increases the length of weak O-H bonds relative to strong ones. Here, the parameterization of Yu et al. (2006) was used, with r 0 = 0.79 Å for bond valence < 0.5 valence units, r 0 = 1.409 Å for bond valence > 0.5 v.u., and b = 0.37 Å in both cases.

Spectroscopy
The infrared spectrum was obtained using a Bruker Alpha FTIR with a diamond Attenuated Total Reflectance attachment (ATR), DTGS (Deuterated Triglycine Sulfate) detector, 4 cm À1 resolution and 4000-450 cm À1 range. The samples were placed on the ATR crystal and pressure exerted by screwing the pressure clamp onto the sample to ensure maximum contact with the ATR crystal. 128 scans were taken for each item and co-added. Band assignments are consistent with those given in Kampf et al. (2013). Numerical values of the spectrum and assignments of the vibration bands are given in Table 3; the spectrum is deposited as a supplementary figure.

Synthesis and crystallization
Dark blue prisms of YCu(TeO 3 ) 2 (NO 3 )(H 2 O) 3 were synthesized hydrothermally. For the synthesis, Y(NO 3 ) 3 Á6H 2 O (Aldrich, 99.8%), Cu(NO 3 ) 2 Á3H 2 O (Sigma-Aldrich !99%) and Te 200 mm mesh (Aldrich, 99.8%) were used as starting materials. A 1:1:1 molar ratio of the reagents in 20 ml water was reacted in a Teflon autoclave bomb at 473 K for 3 days. Crystals of YCu(TeO 3 ) 2 (NO 3 )(H 2 O) 3 were separated manually from a blue powder of undetermined composition in a few percent yield. Several unsuccessful attempts were made to synthesize YCu(TeO 3 ) 2 (NO 3 )(H 2 O) 3 from a stoichiometric mixture of the reagents, using the molar ratio 1:1:2. We also were unsuccessful in producing new compounds, with the same structure type or not, using La, Ce, Nd or Gd in place of Y.

Refinement
Single crystal X-ray diffraction experiments were carried out on the micro-focus macromolecular beam line MX2 of the Australian Synchrotron. Details of data collection and structure refinement are provided in Table 4. Hydrogen atoms H11, H12 and H21 were located during refinement as difference peaks of about one e À / Å 3 occurring at a distance of ca. 0.9-1.0 Å from their nearest oxygen atom. In all cases, short O-H bonds were directed towards another oxygen atom, indicating the existence of hydrogen bonds. Positions were estimated for the remaining hydrogen atoms, assuming water molecule O-H distance near 0.9 Å , H-O-H bond angle near 104 , that O-H vectors were directed to make hydrogen bonds to nearby oxygen atoms, if possible, and that the arrangement of O-H and OÁ Á ÁH around OW3 was approximately tetrahedral. In all cases, residuals of > 0.6 electrons were found close to the expected positions, that could be identified with the H atoms. H positions were finally included in the refinement, assuming full occupancy, isotropic displacement parameters were fixed to 1.5Â of their corresponding O atom and the O-H distance was restrained at 0.90 (3) Å . Computer programs: local program, XDS (Kabsch, 2010), XPREP (Bruker, 2001), SHELXS97 (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015), CrystalMaker (Palmer, 2009) and publCIF (Westrip, 2010).

Crystal data
YCu ( 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.