Crystal structure of cis-bis[4-phenyl-2-(1,2,3,4-tetrahydronaphthalen-1-ylidene)hydrazinecarbothioamidato-κ2 N 1,S]nickel(II) monohydrate tetrahydrofuran disolvate

Crystal structure of a NiII–thiosemicarbazone complex showing an unusual cis arrangement of the N,S-donor ligands and anagostic C—H⋯Ni interactions.

The reaction of Ni II acetate tetrahydrate with the ligand 4-phenyl-2-(1,2,3,4tetrahydronaphthalen-1-ylidene)hydrazinecarbothioamide in a 2:1 molar ratio yielded the title compound, [Ni(C 16 H 16 N 3 S) 2 ]Á2C 4 H 8 OÁH 2 O. The deprotonated ligands act as N,S-donors, forming five-membered metallacycles with the metal ion exhibiting a cis coordination mode unusual for thiosemicarbazone complexes. The Ni II ion is four-coordinated in a tetrahedrally distorted square-planar geometry. Trans-arranged anagostic C-HÁ Á ÁNi interactions are observed. In the crystal, the complex molecules are linked by water molecules through N-HÁ Á ÁO and O-HÁ Á ÁS hydrogen-bonding interactions into centrosymmetric dimers stacked along the c axis, forming rings of graph-set R 4 4 (12). Classical O-HÁ Á ÁO hydrogen bonds involving the water and tetrahydrofuran solvent molecules as well as weak C-HÁ Á Á interactions are also present.

Chemical context
Thiosemicarbazone ligands are N,S-donors that show a wide range of coordination modes (Lobana et al., 2009). As a part of our ongoing project on the synthesis and structures of thiosemicarbazone derivatives and their metal complexes, the crystal structure of an Ni II complex of 2-(1,2,3,4-tetrahydronaphthalen-1-ylidene)-4-phenyl-hydrazinecarbothioamide is reported. The crystal structure of the free ligand was published recently by our group (de Oliveira et al., 2014), but one of the first reports on the synthesis of thiosemicarbazone derivatives was done by Freund & Schander (1902). The complex shows a cis coordination mode, which is unusual for this ligands, and two trans-arranged anagostic interactions between C-H groups and the metal ion are also observed. These interactions are typical for several complexes with catalytic applications (Brookhart et al., 2007).

Structural commentary
In the crystal structure of the title compound, the Ni II cation is four-coordinated by two crystallographically independent deprotonated ligands into discrete complexes that are located in general positions (Fig. 1). The metal displays a remarkable tetrahedrally distorted square-planar coordination geometry (maximum displacement 0.5049 (13) Å for atom N2) with the ligands showing an uncommon cis N 1 ,S-coordination mode. The values of the Ni-N and N-S bond lengths (Table 1) and N2-Ni1-S21 and N22-Ni1-S1 bond angles [164.04 (5) and 162.63 (4) , respectively] confirm the distortion from the ideal coordination geometry. In the complex molecule significant structural changes of the N-N-C-S fragment are observed. For the non-coordinating2-(1,2,3,4-tetrahydronaphthalen-1ylidene)-4-phenyl-hydrazinecarbothioamide ligand, the N-N, N-C and C-S bond lengths amount to 1.385 (2), 1.364 (2) and 1.677 (2) Å . These lengths indicate the double-bond character of the N N and C S bonds, and the single-bond character of the N-C bond (de Oliveira et al., 2014). In contrast, in the title complex the acidic hydrogen of the hydrazine fragment is removed and the negative charge is delocalized over the N-N-C-S fragment. Therefore, the N-N, N-C and C-S bond lengths amount to 1.405 (2), 1.304 (2) and 1.757 (2) Å respectively in one ligand and 1.401 (2), 1.298 (3) and 1.761 (2) Å in the other. The N-C bond lengths indicate a considerable double-bond character, while the N-N and C-S bond distances are consistent with an increased single-bond character. It is worth noting that two trans-arranged anagostic interactions between aromatic C-H groups and the metal ion are observed (Fig. 2). For a threecentre-two-electron MÁ Á ÁH-C agostic interaction, the MÁ Á ÁH distance should range between 1.8 and 2.3 Å and the MÁ Á ÁH-C angle should range between 90 and 140 . For an anagostic interaction these values should range from 2.3 to 2.9 Å and from 110 to 170 , respectively (Brookhart et al., 2007). The title complex shows Ni1Á Á ÁH30 and Ni1Á Á ÁH10 contacts of 2.61 and 2.45 Å [both values are shorter than the sum of the van der Waals radii for Ni (1.63 Å ; Bondi, 1964) and H (1.10 Å ; Rowland & Taylor, 1996)], and C30-H30-Ni1 and C10-H10-Ni1 angles of 118 and 121 , in agreement with the presence of anagostic interactions.

Supramolecular features
The asymmetric unit of the title complex contains one water and two tetrahydrofurane solvate molecules. The water molecules bridge the complex molecules through N-HÁ Á ÁO and O-HÁ Á ÁS hydrogen bonds (Table 2) into centrosymmetric dimers arranged along the c axis, forming rings of graph-set R 4 4 (12) (Fig. 3  Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 40% probability level.  bonds between tetrahydrofurane and water molecules and weak C-HÁ Á Á interactions are observed (Table 2).

Synthesis and crystallization
Starting materials were commercially available and were used without further purification. The synthesis of the ligand was adapted from a procedure reported previously (Freund & Schander, 1902) and its structure is already published (de Oliveira et al., 2014). 2-(1,2,3,4-Tetrahydronaphthalen-1ylidene)-4-phenyl-hydrazinecarbothioamide was dissolved in THF (2 mmol/40 ml) with stirring maintained for 30 min until the solution turned yellow. At the same time, a solution of nickel acetate tetrahydrate (1 mmol/40 ml) in THF was prepared under continuous stirring. A mixture of both solutions was maintained with stirring at room temperature for 6 h. Crystals suitable for X-ray diffraction were obtained by the slow evaporation of the solvent.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The imine and water H atoms were located in difference Fourier map, and were refined as riding with N-H = 0.88, O-H = 0.84 Å , and with U iso (H) = 1.2 U eq (N) or 1.5 U eq (O). All other H atoms were positioned with idealized geometry and refined using a riding model approximation, with C-H = 0.95-0.99 Å and with U iso (H) = 1.2 U eq (C). An outlier (17 0 20) was omitted in the last cycles of refinement.
Computer programs: X-AREA and X-RED32 (Stoe & Cie, 2008), SHELXS97 and SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2006) and publCIF (Westrip, 2010 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.32 e Å −3 Δρ min = −0.48 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0043 (6) 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.