Crystal structure and spectroscopic properties of aquadichlorido{1,1′-[(pyridine-2,6-diyl-κN)bis(methylene)]bis(4-butyl-4,5-dihydro-1H-1,2,4-triazole-5-thione-κN 2)}cobalt(II)

We report here the synthesis, single-crystal structure, electrospray mass spectrum and NMR spectroscopy of a new six-coordinate cobalt(II) pincer complex. The pincer ligand, in this complex, which is novel, coordinates via three nitrogen atoms (two triazole and one pyridine). The ligand is ambidentate and can coordinate via three nitrogen atoms or two sulfur and one nitrogen atoms. The cobalt(II) metal center has pseudo-octahedral geometry and based on the single-crystal structure, the pincer ligand coordinates in a meridional fashion with the metal and adjacent six-membered ring ligands all in a similar plane and forming two slightly distorted boat configurations

The structure of the title compound, [CoCl 2 (C 19 H 27 N 7 S 2 )(H 2 O)], at 173 K has monoclinic (C2/c) symmetry. We report here the synthesis, single-crystal structure, electrospray mass spectrum and NMR spectroscopy of a new sixcoordinate cobalt(II) pincer complex. The pincer ligand, in this complex, which is novel, coordinates via three nitrogen atoms (two triazole and one pyridine). The ligand is ambidentate and can coordinate via three nitrogen atoms or two sulfur and one nitrogen atoms. The cobalt(II) metal center has pseudooctahedral geometry and based on the single-crystal structure, the pincer ligand coordinates in a meridional fashion with the metal and adjacent six-membered ring ligands all in a similar plane and forming two slightly distorted boat configurations. The other two coordinated monodentate ligands are one water molecule and two chloride ions with four cobalt(II) complexes in the unit cell. The asymmetric unit of the complex is comprised of half the pyridine ring and water molecule with the Co II atom at the center of the pincer situated about a twofold axis. The Co-N, Co-O, and Co-Cl bond lengths are consistent with single bonds. In the crystal, the complex forms a three-centre bifurcated weak hydrogen-bonding interaction with a chlorine ion, forming one intermolecular interaction with the pincer group and a water molecule and a second intramolecular interaction with a C-H group within the pincer group. Crystal packing is also highlighted with C 2 2 (6)>a<a infinite chains forming along [001] supported by R 2 2 (8)>a>a ring motifs, forming a three-dimensional supramolecular network structure. While some stacking of the pyridine rings in the unit cell is observed, there are no relevantinteractions in the crystal packing. The 1 H and 13 C{ 1 H} NMR spectra of the complex are consistent with a plane of symmetry being present. The electrospray mass spectrum, which was collected in positive ion mode, showed the loss of one water molecule and one chloride ligand from the complex. In the future, we plan to screen this cobalt(II) complex for electrocatalysis reactivity.
In this study, our aim was to prepare a cobalt(II) pincer complex that contained a pincer ligand precursor with methylene moieties connecting each triazole substituent to the pyridine in the pincer ligand precursor (Fig. 2). We wondered if the cobalt(II) metal center would coordinate to the pincer ligand via three nitrogen atoms as observed for the zinc(II) complex or via sulfur, nitrogen, and sulfur donor atoms. In this communication, we report the preparation, spectroscopic characterization, electrospray mass spectrometry, and single crystal structure of a cobalt(II) pincer complex that contains an ambidentate ligand (Fig. 2).

Structural commentary
We report here the synthesis, single crystal structure, electrospray mass spectrum and NMR spectroscopy of a new sixcoordinate cobalt(II) pincer complex, C 19 H 29 Cl 2 CoN 7 OS 2 , at 173 K whose structure has monoclinic (C2/c) symmetry (Fig. 3). The pincer ligand, in this complex, which is novel, coordinates via three nitrogen atoms (two triazole and one pyridine). The ligand is ambidentate and can coordinate via three nitrogen atoms or two sulfur and one nitrogen atom. The cobalt(II) metal center has a pseudo-octahedral geometry and based on the single crystal structure, the pincer ligand coordinates in a meridional fashion with the metal and adjacent six-membered ring ligands all in a similar plane and forming two slightly distorted boat configurations [Co1/N2/N2/C3/C4/ N4: Q1 = 0.743 (6) Å , = 89.9 , ' = 345.8 (5) ; Co1/N4/C4A/ C3A/N2A/N1A (atoms with the suffix A are generated by the symmetry operation 1 À x, y, Àz + 1 2 ): Q2 = 0.743 (6) Å , = 90.1(5 , ' = 185.3 (5) } (Cremer & Pople, 1975). The other two coordinated monodentate ligands are one water molecule and two chloride ions with four cobalt(II) complexes in the unit cell. The asymmetric unit of the complex is comprised of half the pyridine ring and water molecule with the Co II atom at the center of the pincer situated about a twofold axis. The Co-N, Co-O, and Co-Cl bond lengths are consistent with single bonds. The cobalt-nitrogen (triazole) and cobalt-nitrogen (pyridine) bond lengths are comparable to those previously reported [triazole Co-N = 2.127 (2) and 2.093 (2) Å ; pyridine Co-N= 2.187 (3)  Structure of the ambidentate pincer ligand precursor.

Figure 3
A view of the molecular structure of C 19 H 29 Cl 2 CoN 7 OS 2 , 8, showing the atom-labeling scheme and displacement ellipsoids drawn at the 30% probability level. The molecule crystallizes in the C2/c space group with a twofold rotation axis perpendicular to a c-glide plane along the center of the pincer ligand through to the metal ion transforming the two asymmetric units into the complete complex and containing four cobalt(II) complexes per unit cell. Atoms with the suffix A are generated by the symmetry operation 1 À x, y, Àz + 1 2 .

Supramolecular features
In the crystal, the complex forms a three-centre bifurcated weak hydrogen-bonding interaction (Table 1) with a chlorine ion, forming one intermolecular interaction with the pincer group and a water molecule and a second intramolecular interaction with a C-H group within the pincer group. The crystal packing is also highly supported by R 2 2 (8)>a>a ring motifs, forming a three-dimensional supramolecular network structure (Fig. 4). While some stacking of the pyridine rings in the unit cell is observed, there are no relevantinteractions or classical hydrogen bonds in the crystal packing. The 1 H and 13 C{ 1 H} NMR spectra of the complex are consistent with a plane of symmetry being present. The electrospray mass spectrum, which was collected in positive ion mode, showed the loss of one water molecule and one chloride ligand from the complex (see Fig. S1 in the supporting information). In the future, we plan to screen this cobalt(II) complex for electrocatalysis reactivity.

Database survey
The NNN pincer ligand precursor used in this study is novel. A related NNN pincer ligand, 4, has only been metallated with ZnCl 2 to afford a five-coordinate zinc(II) complex (Miecznikowski et al., 2013). To the best of our knowledge (following a search using Sci-Finder Scholar) no other metal complexes that contain this ligand precursor have been reported in the literature.

Synthesis and crystallization
The preparation of the title complex, 8, and the corresponding ligand precursors 6 and 7 were accomplished according to the scheme below. The precursor for complex 6 has been reported previously (Guino-o et al., 2015).

Figure 4
A view of the packing and the unit cell along the c axis for the title complex, 8. Dashed lines indicate C 2 2 (6)>a<a infinite chains forming along (001) and R 2 2 (8)>a>a ring motifs forming a three-dimensional supramolecular network structure. Stacking of the pyridyl rings face-to-face along the c axis is observed. 55.74 (CH 2 linker), 47.42 (n-butyl CH 2 ), 30.82 (n-butyl CH 2 ), 18.79 (n-butyl CH 2 ), 13.34 (n-butyl CH 3 ).
Analysis The 1 H NMR and 13 C{ 1 H} spectrum of the complex was acquired in DMSO-d 6 . The NMR spectrum was consistent with the title complex. There was not considerable shifting of the proton resonances compared to the starting bis-thione precursor. In the 13 C{1H} NMR spectrum, the C S resonance shifted about 1 ppm to a lower chemical shift value.
The cyclic voltammograms of 7 and 8 are given in Figs. S1 and S2, respectively, in the supporting information. In both 7 and 8 the supporting electrolyte is 0.2 M tetrabutylammonium tetrafluoroborate. The reference electrode is Ag wire, the working electrode is glassy carbon and the counter electrode is a platinum wire. The scan rate is 100 mV s-1.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2