Crystal structure of bis[tetrakis(triphenylphosphane-κP)silver(I)] (nitrilotriacetato-κ4 N,O,O′,O′′)(triphenylphosphane-κP)argentate(I) with an unknown amount of methanol as solvate

The structure of the title compound exhibits a trigonal (P-3) symmetry, with a C 3 axis through all three complex ions, resulting in an asymmetric unit that contains one third of the atoms present in the formula unit. Attempts to refine the solvent model were unsuccessful, indicating uninterpretable disorder, which was handled using SQUEEZE.


Chemical context
Metal nanoparticles are well known in the literature for their use in various applications, e.g., in joining processes , catalysis (Steffan et al., 2009;Zhang et al., 2015) and electronics (Gilles et al., 2013;Scheideler et al., 2015). This is caused by the size and shape-dependent properties of the nanoparticles (Wilcoxon & Abrams, 2006). The formation of nanoparticles requires a metal source, reducing as well as stabilizing agents, and can be achieved by the decomposition of precursors either by heat (Adner et al., 2013) or light (Schliebe et al., 2013). However, to combine the metal source and reducing agents in one molecule, silver (I) carboxylates are convenient compounds. They are known for their light sensitivity and their ability to decompose thermally into elemental silver (Fields & Meyerson, 1976), but due to their low solubility, the corresponding phosphine complexes can also be used. In the context of this approach, the title compound [Ag(C 18 H 15 P) 4 ] 2 [Ag(C 6 H 6 NO 6 )(C 18 H 15 P)], (I), was obtained as a methanol solvate of unknown composition by the reaction of the tri-silver salt of nitrilotriacetic acid with triphenylphosphane.

Figure 3
Crystal packing of the molecular structure of (I) with the view along [001]. All H atoms have been omitted for clarity.

Figure 2
PLUTON cavity plot of the crystal packing of (I) in a view along [110] showing the cavities (pale red) occupied by the disordered methanol solvent. All H atoms have been omitted for clarity. carboxylato-oxygen atoms (Fig. 2). Inter-or intramolecular interactions are not present.

Database survey
Since the first synthesis of nitrilotriacetic acid (Polstorff & Meyer, 1912), a wide diversity of complexes with this molecule containing several metals have been synthesized over the last few decades (Hoard et al., 1968;Dung et al., 1988;Kumari et al., 2012). In contrast, only three crystal structures in which the N atom of nitrilotriacetic acid is bonded to silver(I) are known (Sun et al., 2011;Chen et al., 2005), whereas coordination of the O atom of nitrilotriacetic acid to silver(I) is more common (Novitchi et al., 2010;Sun et al., 2011;Chen et al., 2005;Liang et al., 1964). However, many silver(I) complexes with phosphanes as ligands are known in the literature Rü ffer et al., 2011;Jakob et al., 2005). Likewise, the coordination of four triphenylphosphane ligands to one silver(I) ion has occurred in a variety of possible structural motifs in the last few decades (Pelizzi et al., 1984;Ng, 2012;Bowmaker et al., 1990).

Synthesis of trisilvernitrilotriacetate:
Colorless [(AgO 2 CCH 2 ) 3 N] was prepared by an alternative route to the synthetic methodologies reported by Cotrait and Joussot-Dubien (1966), i.e., by the reaction of nitrilotriacetic acid trisodium salt with [AgNO 3 ] in water at ambient temperature, and with exclusion of light (Noll et al., 2014). It is advisable to consecutively wash the respective silver carboxylate with water and diethyl ether to obtain a pure product.
M All reagents and solvents were obtained commercially and used without further purification.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. C-bonded H atoms were placed in calculated positions and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C) and a C-H distance of 0.93 Å for aromatic and 0.97 Å for methylene H atoms. Attempts to avoid the differences in the anisotropic displacement parameters (Hirshfeld, 1976) of P5 and C45 by using RIGU, SIMU/ ISOR, or EADP instructions were not successful (McArdle, 1995;Sheldrick, 2008).
The crystal contains disordered methanol molecules as the packing solvent. Attempts to refine an adequate disordered solvent model failed, presumably due to the large number of molecules involved and the restraints required for an anisotropic refinement. Thus, the SQUEEZE procedure (Spek, 2015) of PLATON (Spek 2003(Spek , 2009) was used to delete the solvent contribution. This treatment decreased the R 1 value from 0.0920 to 0.0664 and the wR 2 value from 0.2832 to 0.1849 by excluding a volume of 4050.5 Å 3 (40.5% of the total cell volume) and 670 electrons, respectively. The excluded volume is shown in Fig. 2 represented by a PLATON cavity plot (Spek 2003(Spek , 2009) with the spheres representing the cavities that are filled with the disordered solvent. Given the number of electrons excluded by the SQUEEZE procedure, an estimate of about 36 methanol molecules can be calculated for the whole unit cell, which corresponds to approximately six methanol molecules per asymmetric unit. The stated crystal data for M r , etc (Table 1) do not take these into account.   (Sheldrick, 2008); program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and SHELXTL (Sheldrick, 2008); software used to prepare material for publication: WinGX (Farrugia, 2012) and publCIF (Westrip, 2010).

κP)argentate(I) methanol monosolvate
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.34 e Å −3 Δρ min = −0.64 e Å −3 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 > σ(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.