Tris(thiocyanato-κN)tris(triphenylphosphine oxide-κO)europium(III)–(nitrato-κ2 O,O′)bis(thiocyanato-κN)tris(triphenylphosphine oxide-κO)europium(III) (1/1)

The title co-crystal, [Eu(NCS)3(C18H15OP)3][Eu(NCS)2(NO3)(C18H15OP)3], contains two distinct neutral complexes. Each complex has threefold symmetry about its central Eu3+ ion. As a result, the nitrate-containing molecule contains disorder of its bidentate nitrate and two N-bound thiocyanate anions, while the [Eu(NCS)3(OPPh3)3] complex is fully ordered. There is a weak π–π stacking interaction between the phenyl rings of the two molecules [centroid–centroid distance = 4.138 (4) Å].


Related literature
For structural studies on related f-block triphenylphosphine oxide complexes, see: Feazell et al. (2004); Berthet et al. (2003); Long et al. (1999); Bowden et al. (2010). For syntheses and spectroscopic characterization of related compounds, see: Cousins & Hart (1967, 1968  From previous studies, it has been known that lanthanide triphenylphosphine oxide complexes can be prepared with a number of anions including nitrate (Cousins & Hart, 1967;Long et al., 1999), thiocyanate (Cousins & Hart, 1968;Feazell et al., 2004), bromide (Bowden et al., 2010), trifluoromethanesulfonate (Berthet et al., 2003), and iodide (Berthet et al., 2003 (Feazell et al., 2004), likely due to the hard nature of the Ln(III) ions. Also of note is the fact that the title compound contains a 1:3 ratio of Eu(III) to phosphine oxide in both of its complexes, whereas with the larger Nd(III) ion, four triphenylphosphine ligands coordinate. Regarding intermolecular interactions, the title compound contains one weak π-stacking interaction, with plane-to-centroid distances of 3.529 (8) and 3.841 (5) Å, between adjacent rings of the two complexes as illustrated in Fig. 1.
It should be noted that the stoichiometry of the reaction conditions to prepare the title compound were not rigorously controlled and it is likely that the introduced nitrate is a result of a slightly less than 1:3 ratio of Eu(III) to KSCN.

Experimental
Ethanol solutions of europium(III) nitrate hydrate (~1 mmol) and KSCN (~3 mmol) were combined. The resultant solution was decanted from the KNO 3 precipitate. This solution was then mixed with an ethanol solution of triphenylphosphine oxide (~4 mmol). Within one hour, the colorless crystals suitable for the X-ray analysis were isolated.

Refinement
H-atoms were placed in calculated positions and allowed to ride during subsequent refinement, with U iso (H) = 1.2U eq (C) and C-H distances of 0.95 Å.

Figure 1
The molecular structure of I, with the atom-numbering scheme. Displacement ellipsoids for non-hydrogen atoms are drawn at the 50% probability level. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.30 e Å −3 Δρ min = −0.90 e Å −3 Absolute structure: Flack (1983), 3154 Friedel pairs Flack parameter: −0.045 (9) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x