DIMETHYL N-CYANODITHIOIMINOCARBONATE AND TRIPHENYLPHOSPHINE OXIDE METAL HALIDE COMPLEXES: MOLECULAR CRYSTAL ELUCIDATION

Two MX2 (M = Ni, Zn; X = Cl, Br) dimethyl N-cyanodithioiminocarbonate compounds and one CrCl2 triphenylphosphine oxide complex were isolated and elucidated by single crystal X-ray crystallography. NiCl2[(CH3S)2C═NC≡N]2 (1) features inversionrelated hydrogen bonded dimers linked into chains interacting through C−H···Cl growing layers along [110] whose junction into a 3D structure is enabled by H-bonds. ZnBr2[(CH3S)2C═NC≡N]2 (2) also exhibits inversion-related H-bonded dimers. In contrast with 1, the structure of 2 comprises chains along [110], connected via C−H···Br and C−H···S into a 2D layer along [-110]. CrCl2(OPPh3)2 (3) obtaining undergone redox processes, oxidizing [CH3C(O)CH2PPh3] to form PPh3PO, and reducing Cr from Cr to Cr. In the structure, each molecule is linked to height neighbors through H-bonds affording a 3D network.


INTRODUCTION
Dimethyl N-cyanodithioiminocarbonate crystal structures investigations are so far uncommon. Apart crystal structures of Co II and Zn II chloride, and triphenyltin(IV) we earlier reported [1][2][3], only one crystal compound of Cu I chloride has been reported in 1992, by another group [4]. Few investigations report the use of dimethyl Ncyanodithioiminocarbonate as precursor for the isolation of pyrimidines derivatives holding antioxidant properties, and quinazolinone derivatives [5,6]. Our previous works exhibited dimethyl Ncyanodithioiminocarbonate to merely behave as a N-donor ligand, in the solid state, coordinating metal atoms, though containing several basic sites [1][2][3]. Moreover, the ligand disconnects to metal centers, in solution; this might be the main difficulty to its coordinating investigation towards metallic centers in solution [3].
In a former attempt to widen data on the coordination ability of this N-donor ligand, dimethyl Ncyanodithioiminocarbonate has surprisingly undergone redox reactivity at both the cyanide and the imido functionalities, in the presence of chromyl chloride, CrO2Cl2 [11]. Acetonyltriphenylphosphonium can be used as a counter ion to stabilize an anion but may be an O-donor ligand coordinating to metal centers with its oxygen O atom. Very few crystalline compounds relating to acetonyltriphenylphosphonium have been encountered in the literature [12][13][14][15].
Continuing our attempts to broaden data on the coordination ability of these two species viz dimethyl Ncyanodithioiminocarbonate and acetonyltriphenylphosphonium ion, whose crystal structures are merely scarce, we have investigated the reactions in solution media, of dimethyl N-cyanodithioiminocarbonate with nickel(II) chloride hexahydrate or zinc(II) bromide, and acetonyltriphenylphosphonium chloride, CH3C(O)CH2PPh3Cl with chromyl chloride, CrO2Cl2: this has afforded single crystals of NiCl2[(CH3S)2C═NC≡N]2 (1), ZnBr2[(CH3S)2C═NC≡N]2 (2) and CrCl2(OPPh3)2 (3), for which crystallographic X-ray analyses have been carried out and reported in this work.

General
All chemicals were purchased from Sigma-Aldrich, Germany and were used without any further purification. The X-ray crystallographic data for 1, 2 and 3 were collected using a Bruker Kappa X8-APEX-II diffractometer working at 120 K, a Bruker APEX-II DUO diffractometer working at 100 K and an Oxford Diffraction Xcalibur 3/Sapphire3 CCD working at 140 K, respectively. Recrystallization of an amount of the greenish powder in 25 mL of acetone afforded colorless plate-like crystals suitable for a single-crystal X-ray diffraction analysis, after some days of slow solvent evaporation at room temperature (305 K) and finally characterized as 1.

Synthesis of CrCl2(OPPh3)2 (3)
The isolation of 3 occurred by mixing chromyl chloride (CrO2Cl2) [0.4338 g (2.800 mmol)] in 25 mL of acetonitrile and acetonyltriphenylphosphonium chloride, CH3C(O)CH2PPh3Cl [0.4968 g (1.400 mmol)] in 25 mL of acetonitrile. The clear solution that is obtained is subsequently stirred 2h. Colorless block-like crystals suitable for a single-crystal X-ray diffraction study were obtained, after some days of slow solvent evaporation at room temperature (305 K) and characterized as 3.
The proposed equations of reactions leading to the isolation of compounds 1, 2 and 3 are shown as follow: (3)

X-ray crystallography
The X-ray crystallographic data for compound 1 were collected using a Bruker Kappa X8-APEX-II diffractometer at T = 120 (2) K. Data were measured using φ and ω scans using MoKα radiation (λ = 0.71073 Å) using a collection strategy to obtain a hemisphere of unique data determined by Apex3 [16]. Cell parameters were determined and refined using the SAINT program [17]. Data for 1 were corrected for absorption and polarization effects and analyzed for space group determination [18]. The structure was solved by dual-space analysis using SHELXT [19] and the structure refined using least-squares minimization (SHELXL) [20]. The Xray crystallographic data for 2 were collected at T = 100 (2) K using a Bruker DUO diffractometer using MoKα radiation (λ = 0.71073 Å) and an APEXII CCD area detector. Data were measured using φ and ω scans using MoKα radiation using a collection strategy to obtain a hemisphere of unique data determined by Apex2 [21]. Cell parameters were determined and refined using the SAINT program [17]. Data for 2 were corrected for absorption and polarization effects using intensity measurements by SADABS [22]. The structure was solved by dual-space analysis using SHELXT [19] and the structure refined using least-squares minimization (SHELXL) [20]. The X-ray crystallographic data for 3 were collected using an Oxford Diffraction Xcalibur 3/Sapphire3 CCD using MoKα radiation (λ = 0.71073 Å) operating at T = 140 (9) K. Data were measured using φ and ω scans using MoKα (λ = 0.71073 Å) radiation using a collection strategy to obtain a hemisphere of unique data determined by CrysAlisPro (Version 1.171.37.35) [23]. Cell parameters were determined and refined using the CrysAlisPro version 1.171.37.35) [23]. Data for 2 were corrected for absorption and polarization effects by CrysAlisPro (Version 1.171.37.35) empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm [23]. The structure was solved by the direct method using SHELXS [24] and the structure refined using least-squares minimization (SHELXL) [20].
Programs used for the representation of the molecular and crystal structures: Olex2 [25] and Mercury [26]. The Crystallographic data and experimental details for structural analyses of compounds 1, 2 and 3 are summarized in Table 1. Selected bond lengths and angles for 1, 2 and 3 are listed in Tables 2 and 3. CCDC 2057848 (1), 2057849 (2) and 2057850 (3) contain the supplementary crystallographic data for this paper. Copies of these data can be obtained free of charge from the Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK (fax: int. Code +44 1223 336 033 via www.ccdc.cam.ac.uk/data_request/cif).  Table 2. Selected bond lengths (Å) and angles (°) for compounds 1 and 2.

Crystal and molecular structure of compound 1
The complex 1 which crystallizes as colorless plate like-crystals in the triclinic space group P-1, comprises a Ni II metal center coordinated to two chlorides and two cyanide nitrogen atoms from two N-donor dimethyl Ncyanodithioiminocarbonate ligands, to complete the tetrahedron like arrangement (Figure 1). Ni-Cl and Ni−N bond lengths are within expected ranges ( Table 2). The Cl−Ni−Cl angle is larger than an ideal tetrahedral angle while two of the Cl−Ni−N angles and the N−Ni−N angle are smaller and the two remaining Cl−Ni−N angle, slightly longer-smaller, are very close to the ideal tetrahedral angle. A weak distortion is incredibly encountered in this complex 1, whereas N-cyanodithioiminocarbonate bulky ligands might strengthen the distortion [1,2]. The nitrile groups within the N-donor ligands still hold triple-bond character, though the nitrogen atom is coordinated, in a bent fashion, to the Ni center, with C1≡N1 The dihedral angle of 5.60 (6)°, between the least-squares planes of the two dimethyl Ncyanodithioiminocarbonate ligands, indicates that these latter are almost co-planar. Within the structure positioning species, inversion-related pairs of complex molecules are featured. These pairs are arranged such that Cl1 is oriented between the methylthiol H3C−S groups of the adjacent molecule: this presumably damp steric interaction [distances from closest S1 and S3 atoms: 5.9217 (6) and 6.0104 (10) Å, respectively]. Cl2 atom is oriented between methylthiol H3C−S groups of two neighboring molecules from two different pairs so that distances between Cl2 and the two closest S2 and S4 are 8.2791 (11) and 8.1308 (10) Å, respectively ( Figure 2). Inspection of the hydrogen bonding interactions exhibits that inversion-related pairs interact through C3−H3B···Cl1, C7−H7B···Cl1 and C4−H4A···S4 (see Figure 3 and Table 4 for details). The dimers are then connected by C4−H4B···Cl2 into infinite slabs parallel to [110] direction (see Figure 3 and Table 2 for details). In the structure, the infinite slabs are linked through interspecies C8−H8B···Cl2 hydrogen bonds, giving layers along [110] (see Figure 4 and Table 4 for details).
Contrary to the Zn and Co chloride homologues, in the complex 1, the junction of the layers is enabled by C7−H7A···Cl2 hydrogen bonds, leading to the formation of a supramolecular three-dimensional structure ( Figure 5 and Table 4). Thus, complex 1 is structurally different to its reported homologues reported before [1,2].

Crystal and molecular structure of compound 2
The complex 2 crystallizes as colorless block like-crystals in the triclinic space group P-1. The asymmetric unit comprises a Zn II metallic center coordinated by two bromides and two cyanide nitrogen atoms of two N-donor dimethyl N-cyanodithioiminocarbonate ligands ( Figure 6).    These parameters are comparable to those in 1, and are in convenience with those found in the literature [1−4]. Contrary to compound 1, present in this complex 2 is the positioning of the molecules. Indeed, the complex molecules are organized into inversion-related pairs. Thus, Br1 is oriented between the methylthiol H3C−S groups of the adjacent molecule, presumably damping steric interactions [distances from closest S7 and S17 atoms: 6.0873(8) and 6.0391(8) Å, respectively]. Br2 atom is oriented between the methylthiol H3C−S groups of two neighboring molecules from two different pairs such that separating distances between Br2 atom and the two closest S5 and S15 sulfur atoms are 8.2941 (9) and 8.3329 (10) Å, respectively (Figure 7). These values are the ranges of those found in 1. The dihedral angle of 5.97 (6)°, between the least-squares planes of the two dimethyl N-cyanodithioiminocarbonate ligands, indicates a slight deviation from co-planarity. Close inspection of hydrogen bonds exhibits that inversion-related pairs interact via C8−H8A···Br1 and C18−H18A···Br1 (Figure 8 and Table 5). Inversion-related dimers are connected by C16−16A···Br2 affording infinite slabs parallel to the [110] direction ( Figure 8 and Table 5). In the structure, C8−H8C···Br2 and C16−H16B···S15 hydrogen bonds link the chains into a layer-like network (Figure 9), along [-110]. Owing to their involvement ratio in the hydrogen bonded assembly, almost a difference is not observed between Zn−Br1 2.3730 (4) Å and Zn−Br2 2.3510 (4) Å distances. In a structural point of view, the complex 2 is different to complex 1, but is otherwise isomorphous and nearly isostructural to its chloride homologue we earlier published [1,2].

Crystal and molecular structure of compound 3
The complex 3 is the result of a redox process over the chrome complex used as starting material, when the reaction is undertaken in acetonitrile and in a non-controlled atmosphere. Indeed, the acetonyltriphenylphosphonium cation behaves as a reducing agent to reduce Cr VI to Cr II , and is at the same time oxidized forming triphenylphosphine oxide, OPPh3. The methylene carbon atom of the acetonyl group linked to the phosphor atom, as the phosphor atom, has been oxidized and the phosphor atom bears an oxygen atom leading to the formation of the triphenylphosphine oxide, OPPh3 molecule. Thus, removal of the acetonyl group has been observed during the unexpected reaction process; how the CrO2Cl2 and CH3C(O)CH2PPh3Cl play roles in this redox reaction is so far yet unknown. However, an inter-species reorganization happened (equation 3).
The complex 3 crystallizes as colorless block like-crystals in the orthorhombic space group Fdd2. The asymmetric unit consists of Cr II metal center coordinated to two chlorine atoms and two O atoms from two triphenylphosphine oxide (OPPh3) molecules to complete the tetrahedron like-arrangement at chrome atom ( Figure 10). In the past, numerous transition metal crystalline compounds (Mn, Co, Ni, Cu, Zn, Cd; X = Cl, Br, I) of triphenylphosphine oxide, have been isolated and characterized using diverse techniques [27−35]. Almost all known MX2(OPPh3)2 complexes have been isolated from reaction between metal halides and triphenylphosphine oxide, whereas only two examples undergone unexpected reactions, with in situ formation of OPPh3 viz the reactions of the complex [Mn(CH3-η 5 -(CO)2PPh3] with iodine [27], and 1-iodo-6-ptolylethynyl-2,3,4,5tetraethyl-2,3,4,5-tetracarba-nido-hexaborane(6) with ClZnC≡C(CH2)4C≡CZnCl in the presence of Pd(PPh3)4 [28]. In contrast to the general obtaining of MX2(OPPh3)2, this compound 3, the first chrome example, has been obtained from a different reaction route (equation 3). The coordination tetrahedron sphere is considerably distorted with angles varying from 98.12 (11) to 115.22 (6)°. The O-donor triphenylphosphine oxide ligand adopts a general position with bond and angle values in the expected ranges [27−35]. Cr−Cl lengths (Table 3) are not far from those observed for the chloride homologues reported in the literature [29−32]. In the structure, inter-species C−H···Cl hydrogen bonding interactions connect CrCl2(OPPh3)2 molecules. Each CrCl2(OPPh3)2 molecule is linked to eight neighbors ( Figure 11 and Table 6). The expanded hydrogen bonding interactions between the molecules, give rise to a supramolecular three dimensional structure ( Figure 11 and Table 6).

CONCLUSIONS
The salt 1 from inversion-related dimers exhibits infinite chains linked to give layers connected into a supramolecular hydrogen bonded three-dimensional network. In contrast, compound 2 describes inversionrelated dimers whose expanded inter-species hydrogen bonding interactions give rise to a layer-like structure. The compound 3 is isolated from a non-common procedure; its formation evidences redox processes. A reduction is noted over the chromyl chloride complex while the acetonyltriphenylphosphonium cation undergoes an oxidation; Cr VI is reduced to Cr II and in turn oxidized acetonyltriphenylphosphonium forming triphenylphosphine oxide. The interconnections between the molecules in 3 lead to the first hydrogen bonded MX2(PPh3O)2, 3D-structure. Further works involving chromyl chloride and various organic reagents, with the aim of understanding the role of this former, are in progress.