[N,N-Bis(2-hydroxyethyl)dithiocarbamato-κ2 S,S′]bis(triphenylphosphane-κP)copper(I) chloroform monosolvate: crystal structure, Hirshfeld surface analysis and solution NMR measurements

A tetrahedral CuP2S2 coordination geometry is found for the CuI ion in the title compound. The dithiocabamate ligand forms symmetric Cu—S bonds. In the crystal, supramolecular dimers of complex molecules are connected via eight-membered {⋯H—O⋯H—O}2 synthons. In addition, the chloroform molecule participates in Cl⋯π(arene) and S⋯Cl interactions.


Chemical context
The motivation to prepare bis(phosphane)copper(I) dithiocarbamates of general formula (R 3 P) 2 Cu(S 2 CNR 0 R 00 ) (R, R 0 , R 00 = alkyl, aryl) largely stems from the versatile biological properties exhibited by these types of compounds (Skrott & Cvek, 2012;Biersack et al., 2012) and metal dithiocarbamates in general, as summarized in a recent review (Hogarth, 2012). At present, research continues to develop promising antimicrobial agents in light of the growing prevalence of bacterial infections and threats associated with drug-resistant bacteria (Verma & Singh, 2015;Onwudiwe et al., 2016). In our recent efforts to develop anti-microbial agents, phosphanegold(I) dithiocarbamates, R 3 PAu[S 2 CN(iPr)CH 2 CH 2 OH], were prepared and these compounds demonstrated prominent and distinctive anti-microbial activity against a broad range of Gram-positive and Gram-negative bacteria, dependent on the type of P-bound substituent employed (Sim et al., 2014). A distinct structure-activity relationship was noted in that when R = Et, the compound was potent against a broad range of Gram-positive and Gram-negative bacteria, whereas the R = Ph and Cy compounds showed specific activity against Gram- ISSN 2056-9890 positive bacteria. Even greater, broad-range activity is apparent in triethylphosphanegold(I) dialkyldithiocarbamates . The above prompted an exploration of the anti-bacterial activity of related copper(I) and silver(I) derivatives, as these metals are known to possess noteworthy potential as anti-microbial agents (Losasso et al., 2014). Thus, a series of phosphanecopper(I) and silver(I) compounds of general formula (Ph 3 P) 2 M[S 2 CN(R)CH 2 CH 2 OH] for M = Cu and Ag, and R = Me, iPr and CH 2 CH 2 OH, were prepared and evaluated for their anti-microbial activities . While none of the studied compounds exhibited activity against Gram-negative bacteria, they were found to be selectively potent against Gram-positive bacteria. Following new syntheses to evaluate further the potential of this class of compounds, crystals became available for the title complex, (Ph 3 P) 2 Cu[S 2 CN(CH 2 CH 2 OH) 2 ] (I), as its 1:1 chloroform solvate. Herein, the crystal and molecular structures of (I)ÁCHCl 3 are described along with an analysis of its Hirshfeld surface. Finally, some non-standard, e.g. variable temperature, NMR measurements are presented in order to gain insight into the solution structure.

Structural commentary
The molecular structure of the complex in (I)ÁCHCl 3 is shown in Fig. 1 and selected geometric parameters are collected in Table 1. The copper atom is bound by two dithiocarbamate-S atoms and two phosphane-P atoms. The dithiocarbamate ligand is coordinating in a symmetric mode with Á(Cu-S) = 0.042 Å , being the difference between the Cu-S long and Cu-S short bond lengths. This near equivalence in Cu-S bond lengths is reflected in the experimental equivalence of the associated C1-S1, S2 bond lengths. A small disparity, i.e. 0.02 Å , is noted in the Cu-P bond lengths. The resulting P 2 S 2 donor set defines an approximate tetrahedral geometry. A measure of tetrahedral vs square-planar geometry is the value of 4 (Yang et al., 2007) with values of 1.0 and 0.0 corresponding to ideal tetrahedral and square planar geometries, respectively. In the case of the complex in (I)ÁCHCl 3 , the value computes to 0.80. Distortions from the ideal tetrahedral 1800 Tan et al. [Cu(C 5 Table 1 Geometric data (Å , ) for (I) in (I)ÁCHCl 3 and (I) in its 1:1 Ph 3 P cocrystal.  (4) Note: (a) Jian et al. (2000).

Figure 1
The molecular structure of the complex in (I)ÁCHCl 3 , showing the atomlabelling scheme and displacement ellipsoids at the 70% probability level. The solvent CHCl 3 molecule is omitted.

Figure 2
Overlay diagram of (I)ÁCHCl 3 (red image) and (I)ÁPh 3 P (blue). The molecules have been overlapped so the chelate rings are coincident. The CHCl 3 and Ph 3 P molecules have been omitted.
geometry are clearly related to the acute angle subtended by the dithiocarbamate ligand and the wide angle subtended by the bulky triphenylphosphane ligands, Table 1. The structure of (I) has also been determined in its 1:1 cocrystal with PPh 3 (Jian et al., 2000), hereafter (I)ÁPh 3 P, and key geometric parameters for this structure are also included in Table 1. Interestingly, within pairs of comparable bond lengths, those in (I)ÁPPh 3 are systematically longer. However, the value of Á(Cu-S) is slightly less at 0.034 Å . The value of 4 is identical at 0.80. An overlay diagram for (I) in each of (I)ÁCHCl 3 and (I)ÁPPh 3 is shown in Fig. 2 which confirms the very similar conformations adopted for (I) in both structures.

Supramolecular features
Geometric parameters describing the salient intermolecular interactions in the crystal of (I)ÁCHCl 3 are collated in Table 2.
There are two types of hydroxy-O-HÁ Á ÁO(hydroxy) hydrogen bonding in the molecular packing, one intramolecular and the other intermolecular. The former has hydroxy-O2-H as the donor and the hydroxy-O1 as the acceptor, and closes an eight-membered {Á Á ÁHOC 2 NC 2 O} ring. The key feature of the molecular packing is the presence of hydroxy-O-HÁ Á ÁO(hydroxy) hydrogen bonding which connects centrosymmetriclly-related molecules into dimeric aggregates via eight-membered {Á Á ÁH-OÁ Á ÁH-O} 2 synthons, encompassing the intramolecular hydroxy-O-HÁ Á ÁO(hydroxy) hydrogen bonds, Fig. 3a. The only other identifiable directional interactions within standard distance criteria (Spek, 2009) involve the chloroform molecule. Thus, a chloroform-Cl3Á Á Á(arene) interaction is noted, Table 2. In addition, there is evidence for a close S1Á Á ÁCl3 contact, i.e. involving the same chlorine atom as in the just mentioned ClÁ Á Á(arene) interaction. The separation of 3.3488 (9) Å is about 0.2 Å less than the sum of their van der Waals radii (Spek, 2009). In a very recent and exhaustive review of halogen bonding (Cavallo et al., 2016), it was mentioned that sulfur is well known to function as an acceptor in R-XÁ Á ÁS synthons. The interactions involving the chloroform molecule are highlighted in Fig. 3b. Globally, molecules of the copper(I) complex pack to define channels parallel to the c axis in which reside the solvent molecules, Fig. 3c. Given the presence of Ph 3 P ligands in (I)ÁCHCl 3 , evidence was sought for phenylembraces (Dance & Scudder, 1995). While none was apparent for the P1-phosphane, centrosymmetrically related P2-phosphane ligands approach each other in this manner to generate a sixfold phenyl-embrace. The closest interactions between the phosphane residues in this embrace is a pair of edge-to-facephenyl-HÁ Á Á(arene) interactions, i.e. C63-H63Á Á Á(C51-C56) i = 3.25 Å with an angle at H62 of 133 ; symmetry operation (i): 1 À x, 1 À y, 1 À z.

Hirshfeld surface analysis
The protocols for the Hirshfeld surface analysis were as described recently (Yeo et al., 2016). In the present study, analyses were conducted on the following three species: (I) in  Table 2 Hydrogen-bond geometry (Å , ).
Cg1 is the ring centroid of (C51-C56).  analysis provides visualization on the existence of any intermolecular interactions within close proximity in a crystal structure, for which contact distances shorter than the sum of the respective van der Waals radii appear red while at distances equal or longer than this would be white and blue in appearance, respectively. Figs. 4a and b show Hirshfeld surfaces mapped over d norm for (I) and CHCl 3 , respectively. The former image exhibits intense red spots on the surface near the hydroxyethyl substituents which are correlated with the strong O-HÁ Á ÁO hydrogen bonding. Apart from these dominant interactions, several other red spots attributed to the close contacts between the complex and chloroform molecules, i.e. CÁ Á ÁH/HÁ Á ÁC, SÁ Á ÁCl/ClÁ Á ÁS and HÁ Á ÁCl/ClÁ Á ÁH, are evident in Fig. 4a and b.

D-HÁ
The combination of d i and d e distances resulted in twodimensional cuttlefish-and chicken wing-like fingerprint plots for (I), (I)ÁCHCl 3 and CHCl 3 , Fig. 5a, which may be decomposed into several essential close contacts as shown in Fig. 5b-d. In general, complex (I) and its chloroform solvate exhibit almost identical profiles except that the pincer form of (I) in its decomposed fingerprint plot delineated into CÁ Á ÁH/ HÁ Á ÁC contacts shows two different tips at d e + d i $ 2.5 Å and $2.7Å in contrast to the pincer form of (I)ÁCHCl 3 with a pair of symmetrical tips at d e + d i $ 2.7 Å when the solvate is considered as a single entity. The close contact distance (d e + d i $ 2.5 Å ), which is shorter than the sum of van der Waals radii of 2.9 Å (Spek, 2009), is also reflected in the lancet blade-like fingerprint plot of the solvent molecule corresponding to the Cl-HÁ Á ÁC() interaction. The HÁ Á ÁCl/ClÁ Á ÁH contact, on the other hand, contributes to the half-pincer form in the decomposed fingerprint plot of (I) and develops into the full pincer form in (I)ÁCHCl 3 , both with d e + d i $ 2.9 Å that is very close to the sum of van der Waals radii (2.95 Å ). As expected, OÁ Á ÁH/HÁ Á ÁO contacts constitute the strongest among all interactions with d e + d i $ 1.9 Å (cf. the sum of van der Waals radii of 2.75 Å ) in the forceps form of both decomposed fingerprint plots of (I) and (I)ÁCHCl 3 , Fig. 5d. Based on the asymmetric fingerprint patterns of the CÁ Á ÁH/ HÁ Á ÁC and ClÁ Á ÁH/HÁ Á ÁCl contacts, Fig. 5b and c, and the symmetric pattern of the OÁ Á ÁH/HÁ Á ÁO contacts, Fig. 5d, it may be concluded that two complex molecules are very closely associated, as shown in Fig    Despite this, not all of these contacts result in meaningful interactions based on the comparison between d e + d i contact distances and the sum of the van der Waals radii. This sequence is followed by OÁ Á ÁH/ HÁ Á ÁO contacts which form the fourth most dominant interactions with a contribution of approximately 4.6% to the overall Hirshfeld surface. In general, there is not much deviation of the topological distribution between (I) and (I)ÁCHCl 3 except that the contribution from HÁ Á ÁCl/ClÁ Á ÁH increases by nearly twofold upon the inclusion of the solvent molecule in (I)ÁCHCl 3 . As for the chloroform molecule, HÁ Á ÁCl/ClÁ Á ÁH makes the major contribution at 74.4%, followed by 8.9% from HÁ Á ÁH and 8.4% from HÁ Á ÁCl/ClÁ Á ÁH; the remaining contributions from other minor contacts.
As mentioned previously, ClÁ Á Á(arene) and SÁ Á ÁCl interactions are formed by the chloroform molecule. In order to gain insight into the charge distribution and rationalize these close contacts, the electrostatic potential (ESP) was mapped over the Hirshfeld surface by ab initio Hartree-Fock (HF) quantum modelling with the 6-31G(d) basis set, as this represents the best possible level of theory and basis set functions in this study so as to keep the accuracy and computational cost at manageable level.
As shown in Fig. 7a, a phenyl ring of the complex molecule exhibits mild electronegative character as evidenced from the pale-red spot on the ESP map in contrast to the strong electropositive character about CHCl 3 , being intense-blue. The electropositive character of the methine group extends slightly beyond the chloro atom approaching its equatorial ring of the negative charge region, hence establishing the weak ClÁ Á Á(arene) interaction with d e + d i $ 3.3 Å being slightly less than the sum of van der Waals radii of 3.45 Å . The SÁ Á ÁCl halogen bond, on the other hand, is established through the highly directional interaction between the electronegative sulfur of (I) and the -hole of the chloro atom of CHCl 3 with weak electropositive character, Fig. 7b. The electropositive character of the -hole results from the electron deficiency in the outer lobe of the p orbital (non-bonded) when a half-filled p orbital of a halogen participates in the formation of covalent bond (Clark et al., 2007).

NMR Study
FT NMR spectra were recorded on a Bruker AVANCE III 400 MHz spectrometer, operating at 400.13, 100.61 and 161.98 MHz, respectively, for 1 H, 13 C and 31 P. Spectra were indirectly referenced to the solvent deuterium lock shift; chemical shifts are quoted relative to TMS and 85% H 3 PO 4 . Probe temperatures were controlled by a standard variable temperature unit and are considered accurate to within AE1 K. Spectra were acquired on approximately 14 mmol solutions of (I) in each of CD 2 Cl 2 , d 6 -DMSO and CDCl 2 CDCl 2 .
The ambient temperature (298 K) 1 H NMR spectra of (I) display the expected signals due to the triphenylphosphine and dithiocarbamate ligands. The spectra are qualitatively identical in all three solvents, with the only significant differences being the position of the -OH signal of the dithiocarbamate ligand.
The aromatic region of the 1 H spectrum in d 6 -DMSO shows two multiplets at ca 7.39 ppm (6 H) and 7.28 ppm (24 H     CHCl 3 , as seen in the X-ray crystal structure analysis. The dithiocarbamate moiety displays a single set of resonances, indicating the two -CH 2 CH 2 OH groups are chemically equivalent. The -OH groups display a triplet at 4.80 ppm ( 3 J HH = 5.3 Hz), which disappears on the addition of D 2 O. The methylene hydrogen atoms display a triplet at 3.96 ppm ( 3 J HH = 6.4 Hz) and a pseudo quartet at 3.65 ppm, assignable to NCH 2 -and -CH 2 OH, respectively. On the addition of D 2 O, the quartet collapses to a triplet.
The 13 C{ 1 H} spectra in each of the solvents are also qualitatively identical. In d 6 -DMSO solution, the carbon atoms of the triphenylphospine ligands give rise to four resonances at 134.6 ppm (very weak, d, 1 J PC $22 Hz, C ipso ), 133.6 ppm (d, 2 J PC = 12 Hz, C ortho ), 130.1 ppm (s, C para ) and 128.9 ppm (d, 3 J PC = 5.70 Hz, C meta ). The dithiocarbamate ligand shows two signals due to the methylene carbon atoms at 58.7 ppm (NCH 2 -) and 56.0 ppm (-CH 2 OH), respectively. The quaternary carbon atom of the dithiocarbamate was not observed.
The ambient temperature 31 P{ 1 H} spectrum in CD 2 Cl 2 displays as single, broad resonance at À1.55 ppm (Áv 1/2 = 280 Hz). The line broadening is attributed to rapid relaxation of Cu via the quadrupole relaxation (QR) mechanism. Quadrupole relaxation is strongly temperature dependent: the rate of relaxation increases as the temperature decreases. On cooling, the signal sharpens progressively: Áv 1/2 (203 K) $35 Hz. The sharpening presumably arises because of the effective 'decoupling' of the 65 Cu-31 P and 63 Cu-31 P scalar couplings as the rate of (Cu) relaxation increases (Grace et al., 1970). The addition of ca 2 mg (0.9 equivalents) of triphenylphosphine at ambient temperature, to putatively give (I)ÁPPh 3 , gives a single, broad peak at ca À3 ppm, which is between the chemical shifts of pure (I) and free PPh 3 (ca À6 ppm), indicating rapid exchange of the triphenylphosphine ligands.
In an attempt to resolve the Cu-P J couplings, 31 P{ 1 H} spectra were recorded in CDCl 2 CDCl 2 solution at elevated temperatures (to reduce the rate of QR). However, no significant changes were observed in the line widths on elevating the temperature to 328 K, and any Cu-P coupling, if not lost through reversible ligand dissociation, remained unresolved. There was no evidence of decomposition at higher temperatures in this solvent.
There are two key conclusions from the foregoing. Firstly, the experiments with D 2 O proving exchange of the hydroxy-H atom indicates that this atom is labile, suggesting functionalization at this group should, in principle, be feasible. Secondly, the presence of additional Ph 3 P in solution does not result in displacement of the dithiocarbamate ligand nor force a monodentate mode of coordination proving the stability of complex (I) in each of (I)ÁCHCl 3 and (I)ÁPPh 3 , and in solution.

Synthesis and crystallization
All chemicals and solvents were used as purchased without purification, and all reactions were carried out under ambient conditions. The melting point was determined on a Biobase automatic melting point apparatus MP450. The IR spectrum was obtained on a Perkin Elmer Spectrum 400 FT Mid-IR/Far-IR spectrophotometer from 4000 to 400 cm À1 ; abbreviations: br, broad; m, medium; s, strong.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Carbon-bound H atoms were placed in calculated positions (C-H = 0.95-1.00 Å ) and were included in the refinement in the riding-model approximation, with U iso (H) set to 1.2U eq (C). Refinement of the O-bound H atoms proved unstable so these atoms were fixed in the model in the positions revealed by a difference Fourier map, with U iso (H) = 1.5U eq (O). The maximum and minimum residual electron density peaks of 1.97 and 1.93 e Å À3 , respectively, were located 0.78 and 0.62 Å from the Cl1 atom. While this feature of the difference map might indicate disorder, additional peaks that might be anticipated for the other atoms in the disordered component of chloroform molecule were not evident. This, plus the observation that the anisotropic displacement parameters of the atoms comprising the chloroform molecule exhibited no unusual features, suggest the residual electron densities have limited chemical significance. Finally, owing to poor agreement, four reflections, i.e. (326), (115), (666) and (142) , were omitted from the final cycles of refinement.  (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015), ORTEP-3 for Windows (Farrugia, 2012), QMol (Gans & Shalloway, 2001), DIAMOND (Brandenburg, 2006) and publCIF (Westrip, 2010). SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012), QMol (Gans & Shalloway, 2001) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

[N,N-Bis(2-hydroxyethyl)dithiocarbamato-κ 2 S,S′]bis(triphenylphosphane-κP)copper(I) chloroform monosolvate
Crystal data [Cu(C 5 H 5  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 1.97 e Å −3 Δρ min = −1.93 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.