Diaquatris[4,4,4-trifluoro-3-oxo-1-(thiophen-2-yl)but-1-en-1-olato]neodymium(III) acetonitrile monosolvate

The title complex, [Nd(C8H4F3O2S)3(H2O)2]·CH3CN, consists of an NdIII ion surrounded by three 4,4,4-trifluoro-3-oxo-1-(thiophen-2-yl)but-1-en-1-olate ligands, coordinated through the O atoms, and two water molecules. The Nd—O bond lengths range from 2.372 (2) to 2.513 (2) Å. The metal ion displays a coordination number of eight and a square-antiprismatic coordination geometry. A single uncoordinated acetonitrile molecule is present in the asymmetric unit. Two of the three thiophene rings are disordered, resulting from a 180° rotation with respect to the β-diketonate moiety. The coordinated water molecules act as hydrogen-bond donors towards the acetonitrile N atom and the β-diketonate O atoms.

The title complex, [Nd(C 8 H 4 F 3 O 2 S) 3 (H 2 O) 2 ]ÁCH 3 CN, consists of an Nd III ion surrounded by three 4,4,4-trifluoro-3-oxo-1-(thiophen-2-yl)but-1-en-1-olate ligands, coordinated through the O atoms, and two water molecules. The Nd-O bond lengths range from 2.372 (2) to 2.513 (2) Å . The metal ion displays a coordination number of eight and a squareantiprismatic coordination geometry. A single uncoordinated acetonitrile molecule is present in the asymmetric unit. Two of the three thiophene rings are disordered, resulting from a 180 rotation with respect to the -diketonate moiety. The coordinated water molecules act as hydrogen-bond donors towards the acetonitrile N atom and the -diketonate O atoms.

Related literature
The title complex has been studied for its near-infrared emitting properties and as a standard for near-infrared emission quantum yield measurements, see: Rusakova et al. (1992a,b); Voloshin et al. (2000). For the Eu III analog, see: White (1976). A similar Nd III complex with trifluoroacetyl-4-(thiophen2-yl)acetonato ligands but with triphenylphosphine oxide instead of water molecules as the ancillary ligands was described by Leipoldt et al. (1975).

Comment
For determining emission efficiencies of sensitized lanthanide luminescence in the NIR region of the spectrum, a Nd III complex with 4,4,4-trifluoro-3-oxo-1-(thiophen-2-yl)but-1-en-1-olate (TTA) (Scheme 1) is used as a standard (Rusakova et al., 1992a). We synthesized the complex and isolated X-ray quality single crystals. The structure shown in Figure 1 was obtained. The Nd III is surrounded by three TTA ligands, coordinated through the oxygen atoms, and two water molecules. Two TTA ligands are in the same plane while the remaining one is almost perpendicular to that plane with an angle of 87.6°. A single uncoordinated acetonitrile molecule crystallized within the asymmetric unit. Two of the three thiophene rings are disordered, as seen for many structures involving thiophene moieties. Modeling the disorder gives two different positions for the thiophene rings, where they are rotated 180° around the C-C bond to the beta-diketone. The occupancy factors for both disordered rings are 59 and 61% for the major component. Figure 2 shows the coordination polyhedron around the Nd III , which can be described as a slightly distorted square antiprism. The Nd III -O bond distances are in the range 2.372 (3)-2.513 (3) Å with the TTA ligands displaying the shorter bond lengths. These distances compare well with a similar structure of Nd III with TTA reported by Leipoldt et al. (1975), with the formula [Nd(TTA) 3 (TPPO) 2 ] (TPPO=triphenylphosphine oxide). In distances are slightly longer than the distances in the complex discussed here. An isostructural Eu(III) complex has also been reported by White (1976). Due to slow decomposition of the crystals of the Eu(III) complex the data reported were poor, but the weak hydrogen bonding interactions were shown to be in the range D···A = 2.9-3.0 Å.

Experimental
The title compound was synthesized by a previously reported procedure (Voloshin et al. 2000). Crystals were isolated from a saturated solution of acetonitrile and water (v/v = 1:5) upon standing at room temperature.

Refinement
Hydrogen atoms were positioned geometrically using a riding model with C-H = 0.95, 0.99 and 0.98 Å for aromatic CH and aliphatic CH 2 and CH 3 hydrogen atoms, respectively, and U iso (H)=1.2-1.5 U eq (C). Hydrogen atoms of the water molecules were found in the difference map and their thermal parameters constrained to the parent atoms. Two thiophene rings are disordered through a 180° rotation with respect to the C-C bond to the β-diketonato moiety. The disorder was modeled by allowing the occupancy factors of the two possible ring positions to freely refine to 61 and 59% for the major components. The bond distances for the major and minor components were restrained with the SAME command and the thermal displacement paramenters of both ring atom components restrained with the EADP command. Fig. 1. Thermal ellipsoid plot of the title complex with atom numbering (except hydrogen atoms) and 50% probability displacement ellipsoids for non-hydrogen atoms. Only the major component of the disordered thiophene rings is shown.  Diaquatris[4,4,4-trifluoro-3-oxo-1-(thiophen-2-yl)but-1-en-1-olato]neodymium(III) acetonitrile monosolvate Crystal data [Nd(C 8