Bis(N,N-diethyldithiocarbamato-κ2 S,S′)(3-hydroxypyridine-κN)zinc and bis[N-(2-hydroxyethyl)-N-methyldithiocarbamato-κ2 S,S′](3-hydroxypyridine-κN)zinc: crystal structures and Hirshfeld surface analysis

Highly-distorted five-coordinate NS4 coordination geometries are found in each of Zn(S2CNEt)2(pyOH) and Zn[S2CN(Me)CH2CH2OH]2(pyOH); pyOH is 3-hydroxypyridine. In their respective crystals, hydrogen bonding leads to dimeric aggregates in the former (O—H⋯S) and supramolecular chains in the latter (O—H⋯O, S).

An approach to increase the supramolecular aggregation in the crystal structures of zinc dithiocarbamates has been to introduce hydrogen bonding functionality into the ligands, i.e using dithiocarbamate anions of the type À S 2 CN(R)CH 2 CH 2 OH. This influence is seen in the recent report of the structures of Zn[S 2 CN(R)CH 2 CH 2 OH] 2 (2,2 0bipyridyl) for R = i-Pr and CH 2 CH 2 OH (Safbri et al., 2016). The common feature of these structures along with those of related species with no hydrogen bonding potential, e.g.

Structural commentary
Two independent molecules of Zn(S 2 CNEt 2 ) 2 (pyOH) comprise the asymmetric unit of (I), Fig. 1; pyOH is The molecular structures of the two independent molecules comprising the asymmetric unit in (I), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level.
3-hydroxypyridine. For the Zn1-containing molecule, Fig. 1a, the Zn II atom is chelated by two dithiocarbamate ligands and one nitrogen atom derived from the monodentate pyOH ligand. The S1-dithiocarbamate ligand chelates the zinc atom forming quite different Zn-S bond lengths compared with the S3-dithiocarbamate ligand. This is quantified in the values of Á(Zn-S), being the difference between the Zn-S long and Zn-S short bond lengths, Table 1, i.e. 0.43 and 0.15 Å , respectively. The Zn1-N3 bond length is significantly shorter than the Zn-S bonds. The NS 4 coordination geometry is highly distorted as seen in the value of of 0.48 (Addison et al., 1984).
This value is almost exactly intermediate between the ideal square pyramidal geometry with = 0.0 and ideal trigonal pyramidal with = 1.0. The acute S-Zn-S chelate angles contribute to this distortion, Table 1. The widest angles in the coordination geometry are subtended by S s -Zn-S s (s = short) and, especially, the S l -Zn-S l (l = long) bond angles, Table 1. The coordination geometry for the Zn2 atom, Fig. 1b, is quite similar to that just described for the Zn1 atom. The values of Á(Zn-S) of 0.21 and 0.25 Å are intermediate to those for the Zn1-molecule. Even so, the differences in the Zn-S bond lengths in both molecules are not that great with this observation reflected in the closeness of the C-S bond lengths, Table 1. The value of for the Zn2-molecule is 0.53, indicating an inclination towards trigonal bipyramidal cf. the Zn1-molecule.
The molecular structure of (II), Zn[S 2 CN(Me)CH 2 -CH 2 OH] 2 (pyOH), is shown in Fig. 2  The molecular structure of (II), showing the atom-labelling scheme and displacement ellipsoids at the 70% probability level.

Figure 3
Overlay diagrams for the Zn1-and Zn2-molecules in (I) and the molecule in (II) shown as red, green and blue images, respectively: (a) approximately side-on to the pyOH ring and (b) along the N-Zn bond. The molecules are overlapped so that the pyOH rings are coincident.
of the dithiocarbamate ligands in (II) are close to those observed for the Zn1-molecule in (I) with Á(Zn-S) values of 0.42 and 0.19 Å . The difference between (I) and (II) is found in the coordination geometry which is close to square pyramidal in (II), as seen in the value of = 0.16. In this description, the S1-S4 atoms define the basal plane with the r.m.s. deviation being 0.0501 Å . The Zn atom lies 0.7514 (4) Å above the plane in the direction of the N3 atom. The dihedral angle between the chelate rings is 63.81 (15) , an angle significantly greater than for the comparable angles in (I), Table 1. Overlay diagrams of the three molecules in (I) and (II) are shown in Fig. 3. The molecules have been overlapped so that the pyOH rings are coincident. The differences in the conformations of the molecules comprising (I) are clearly seen, and especially between these and the conformation in (II). Such variability in structure reflects the flexibility in the binding modes of the dithiocarbamate ligands leading to quite distinctive coordination geometries.

Supramolecular features
The key feature of the molecular packing of (I) is the formation of hydroxy-O-HÁ Á ÁS(dithiocarbamate) hydrogen bonds that sustain centrosymmetric, dimeric aggregates, via a 14-membered {Á Á ÁHOC 2 NZnS} 2 synthon, Fig. 4a and Table 2. Additional stabilization to the dimer is provided by an intradimerinteraction between the pyOH rings. The intercentroid distance is 3.5484 (18) Å and the angle of inclination is 3.91 (14) for symmetry operation 1 À x, 1 2 + y, 1 2 À z. The aggregates are further stabilized by pyOH-C-HÁ Á Á inter-actions where the -system is a chelate ring. Such C-HÁ Á Á(chelate) interactions are increasingly being recognized as being important in the supramolecular chemistry of metal 1,1-dithiolates (Tiekink & Zukerman-Schpector, 2011;Tan et al., 2016a) and, it should be noted, routinely appear in the output from PLATON (Spek, 2009). Connections between aggregates leading to supramolecular layers in the ab plane are also of the type C-HÁ Á Á(chelate) but with methyl-H atoms as the donors, Fig. 4b. The connections between layers along the c direction are of the type methylene-C-HÁ Á ÁO(hydroxy), Fig. 4c.
The addition of greater hydrogen-bonding potential in (II) results in an infinite chain, Table 3. There is an hydroxy-O-HÁ Á ÁO(hydroxy) hydrogen bond involving the O2 and O1 atoms as the donor and acceptor, respectively. The O1hydroxy group forms a hydrogen bond with a dithiocarbamate-S2 atom. As shown by the '1' in Fig. 5a, these hydrogen bonds lead to a centrosymmetric 22-membered {Á Á ÁSZnSCNC 2 OHÁ Á ÁOH} 2 synthon. On either side of these   Table 2 Hydrogen-bond geometry (Å , ) for (I).

D-HÁ
Cg1 is the centroid of the (Zn,S3,S4,C5) chelate ring. synthons, the pyOH hydroxy group hydrogen bonds to the O2hydroxy atom and through symmetry, a centrosymmetric 24membered {Á Á ÁOC 2 NCSZnNC 2 OH} 2 synthon is formed, highlighted as '2' in Fig. 5a. Alternating synthons generate a supramolecular chain aligned along the c axis. Methylene-C-HÁ Á Á(chelate) interactions link molecules into dimeric units, Fig. 5b. The combination of the aforementioned interactions lead to supramolecular layers that stack along the b axis with no directional interactions between them, Fig. 5c.

Hirshfeld surface analysis
The Hirshfeld surface analysis for (I) and (II) was performed as described recently (Cardoso et al., 2016). From the views of the Hirshfeld surface mapped over d norm in the range À0.2 to + 1.3 au for the Zn1-and Zn2-containing molecules of (I), Fig. 6, the presence of bright-red spots near the hydroxy-H1O and -H2O, and dithiocarbamate-S2 and S8 atoms represent the donors and acceptors of the O-HÁ Á ÁS hydrogen bonds; these are viewed as blue and red regions on the Hirshfeld surfaces mapped over electrostatic potential (mapped over the range À0.07 to +0.10 au), Fig. 7, corresponding to positive and negative potentials, respectively. The faint-red spots appearing near the hydroxy-O2 and methyl-C19 atoms in Fig. 6b and 6c are due to comparatively weaker intermolecular C-HÁ Á ÁO interactions. The intra-dimerstacking interaction between the pyOH rings, Fig. 4a, is evident through the appearance of faint-red spots near the arene-C13 and C26 atoms of the rings, Fig. 6a and 6b, forming a close interatomic CÁ Á ÁC contact, Table 4. The diminutive-red spots near the pyOH-H13 and -H28 and dithiocarbamate-C21 atoms, Fig Views of the Hirshfeld surfaces for (I) mapped over d norm for the (a) Zn1molecule and, (b) and (c) Zn2-molecule.

Figure 5
The molecular packing in (II), (a) supramolecular chain mediated by hydroxy-O-HÁ Á ÁO(hydroxyl), S(dithiocarbamate) hydrogen bonding, shown as orange and blue dashed lines, respectively, and non-acidic H atoms omitted, (b) detail of methylene-C-HÁ Á Á(chelate) interactions shown as purple dashed lines and (c) view of the unit-cell contents shown in projection down the a axis, with one layer shown in space-filling mode. Table 4 Summary of short interatomic contacts (Å ) in (I) and (II).

Contact
Distance Symmetry operation   immediate environments around reference molecules showing above intermolecular interactions are illustrated in Fig. 8. The presence of peripheral hydroxy groups participating in the O-HÁ Á ÁO hydrogen bonds in the structure of (II) result in the distinct bright-red spots near the respective donors and acceptor atoms on the Hirshfeld surface mapped over d norm , Fig. 9a and 9b, and result in the blue and red regions corresponding to positive and negative potential on the Hirshfeld surface mapped over electrostatic potential (mapped over the range À0.12 to +0.18 au), Fig. 9c. The faint-red spots near the S4, C8, C9 and H2B atoms in Fig. 9a and 9b indicate their involvement in short interatomic SÁ Á ÁS, CÁ Á ÁC and CÁ Á ÁH/ HÁ Á ÁC contacts, Table 4. Fig. 10a illustrates the immediate environment about a reference molecule within Hirshfeld surfaces mapped over electrostatic potential and highlights the O-HÁ Á ÁO hydrogen bonds. The C-HÁ Á Á(chelate) and its reciprocal contact, i.e. -HÁ Á ÁC, and short interatomic SÁ Á ÁS, CÁ Á ÁC and CÁ Á ÁH/HÁ Á ÁC contacts, with labels 3-6, are shown in Fig. 10b.
The overall two-dimensional fingerprint plot for individual Zn1-and Zn2-containing molecules, overall (I) and (II) are illustrated in Fig. 11a. The respective plots delineated into HÁ Á ÁH, OÁ Á ÁH/HÁ Á ÁO, SÁ Á ÁH/HÁ Á ÁS, CÁ Á ÁH/HÁ Á ÁC, CÁ Á ÁC and SÁ Á ÁS contacts (McKinnon et al., 2007) are shown in Fig. 11b-g, respectively; the relative contributions from different contacts to the Hirshfeld surfaces of (I) and (II) are summarized in Table 5.    The fingerprint plots delineated into HÁ Á ÁH contacts for (I), Fig. 11b, show different distributions of points in the individual plots for Zn1-and Zn2-molecules. This, as well as their different percentage contributions to the Hirshfeld surface, Table 5, confirm their distinct chemical environments. The overall plot is the superimposition of these individual plots with a pair of small peaks, at (d e , d i ) distances shorter than their van der Waals separations, corresponding to short interatomic HÁ Á ÁH contacts, Table 4, between the hydrogen atoms of the Zn1-molecule.
The fingerprint plots delineated into OÁ Á ÁH/HÁ Á ÁO contacts, Fig. 11c, also exhibit slightly different profiles for the independent molecules. The respective peaks at d e + d i $ 2.7 Å and $ 2.6 Å correspond to donors (upper region) and the acceptors (lower region) for the Zn1-molecule, whereas these appear as a pair of peaks at the same d e + d i $ 2.6 Å distance for the Zn2-molecule. This is likely due to the interacting oxygen and hydrogen atoms for the Zn1-molecule being at their van der Waals separation in the donor region, i.e. at 2.72 Å , while in the acceptor region the peak corresponds to a short interatomic OÁ Á ÁH contact, Table 4. In the plot for the Zn2-molecule, this contact gives rise to the pair of peaks at d e + d i $ 2.6 Å .
The pair of spikes with their tips at different d e + d i distances in the fingerprint plots delineated into SÁ Á ÁH/HÁ Á ÁS contacts, Fig. 11d, for the Zn1-and Zn2-molecules result from different hydroxy-O-HÁ Á ÁS(dithiocarbamate) hydrogen bonds. The tips at d e + d i $ 2.4 Å in the donor region of the plot for the Zn1-molecule and in the acceptor region for the Zn2-molecule are due to the formation of O-HÁ Á ÁS hydrogen bonds between the hydroxy-O1 and dithiocarbamate-S8 atoms; the other hydrogen bond, involving the O2 and S2 atoms, gives rise to tips at d e + d i $ 2.3 Å in the respective donor and acceptor regions of the plots, Fig. 11d. The plot for the overall structure results from the superimposition of individual plots and shows the symmetric distribution of points as a pair of long spikes having tips at d e + d i $ 2.3 Å . The short interatomic SÁ Á ÁH/HÁ Á ÁS contacts in the crystal of (I), Table 4, appear as a pair of aligned green points beginning at d e + d i $ 3.0 Å in the respective plots.
Almost the same percentage contribution from CÁ Á ÁH/ HÁ Á ÁC contacts to the overall surface is made by the Zn1-and Zn2-molecules, Table 5, and the respective fingerprint plots, Fig. 11e, have the same shape with tips at d e + d i $ 2.7 Å which are due to the short interatomic CÁ Á ÁH/HÁ Á ÁC contacts, Table 4, involving the atoms forming the C-HÁ Á Á(chelate) interactions; the points corresponding to the other short CÁ Á ÁH/HÁ Á ÁC contacts are within the plot. The CÁ Á ÁC contacts assigned to intra-dimerstacking interactions between pyOH-rings have a small, i.e. 1.8%, but recognizable contribution to the Hirshfeld surface and appear as an arrow-like distribution of points around d e = d i = 1.8 Å in Fig. 11f. As indicated in Fig. 11g, SÁ Á ÁS contacts do not figure prominently in the molecular packing of (I).
The corresponding two-dimensional fingerprint plots for (II) are also given in Fig. 11. In the fingerprint plots delineated into HÁ Á ÁH contacts, Fig. 11b   bond between the pyOH-O3 and hydroxy-O2 atoms results in a short interatomic HÁ Á ÁH contact between the H2O and H3O atoms, Table 4. The increase in the percentage contribution from OÁ Á ÁH/HÁ Á ÁO contacts to the Hirshfeld surface and the corresponding decrease in the contribution from HÁ Á ÁH contacts in (II), cf. (I), Table 5, is due to the presence of dominating O-HÁ Á ÁO hydrogen bonds in the crystal of (II) and is characterized as a pair of long spikes terminating at d e + d i $ 1.8 Å , Fig. 11c. The tips corresponding to the O1Á Á ÁH6A contact, Table 4, are diminished within the long spikes corresponding to dominant O-HÁ Á ÁO hydrogen bonds. The SÁ Á ÁH/HÁ Á ÁS contacts with the nearly same contribution to the surface of (II) as for (I), i.e. 22.2 and 22.7%, respectively, reflect the O-HÁ Á ÁS hydrogen bonds and additional SÁ Á ÁH contacts resulting in tips at d e + d i $ 2.9 Å in Fig. 11d and Table 4. The 12.3% contribution from CÁ Á ÁH/ HÁ Á ÁC contacts to the surface with the tips at d e + d i $ 2.6 Å in the plot, Fig. 11e, results from the C-HÁ Á Á(chelate) and short interatomic CÁ Á ÁH/HÁ Á ÁC contacts, Table 4. The presence of C-HÁ Á Á(chelate) interactions is also indicated by the short interatomic ZnÁ Á ÁH/HÁ Á ÁZn contacts summarized in Table 4. The presence of short interatomic CÁ Á ÁC contacts between symmetry-related methyl-C8 atoms is identified in the respective plot, Fig. 11f, as the pair of tips at d e + d i $1.7 Å . Finally, a cone-shaped distribution of points with a 3.8% contribution to the surface from SÁ Á ÁS contacts having a vertex at d e = d i $ 1.7 Å in the fingerprint plot, Fig. 11g, results from short interatomic contacts between S4 atoms, Table 4; the absence of analogous contacts in (I) results in a very low percentage contribution to its surface (see above).

Database survey
As alluded to in the Chemical context, the presence of hydroxyethyl groups in zinc dithiocarbamates leads to a higher degree of recognizable supramolecular aggregation owing to hydrogen bonding, usually of the type hydroxy-O-HÁ Á ÁO(hydroxy) but, sometimes also of the type hydroxy-O-HÁ Á ÁS(dithiocarbamate) (Tan et al., 2013;Jamaludin et al., 2016). The following is a brief overview of some previous structures with ethylhydroxydithiocarbamate ligands highlighting the important role of hydrogen bonding in the supramolecular aggregation. In the what might be termed the parent binary compound, i.e. {Zn[S 2 CN(CH 2 CH 2 OH) 2 ] 2 } 2 , the usual dimeric motif is evident but these self-assemble via strong hydrogen bonding into three-dimensional architectures in both of the polymorphs characterized thus far, with the difference between the structures being the topology of supramolecular layers, i.e. flattened (Manohar et al., 1998) and undulating (Benson et al., 2007). When one ethylhydroxy group is replaced by an ethyl group, as in {Zn[S 2 CN(Et)CH 2 CH 2 OH] 2 } 2 , the reduced hydrogen bonding leads to supramolecular chains (Benson et al., 2007). Bridging ligands lead to zero-dimensional aggregates, e.g. in   (Farrugia, 2012), QMol (Gans & Shalloway, 2001), DIAMOND (Brandenburg, 2006) and publCIF (Westrip, 2010).
hydrogen bonding of the type hydroxy-O-HÁ Á ÁO(hydroxy) links the molecules into inter-woven double chains (Poplaukhin & Tiekink, 2008). The interesting structural chemistry is complimented by observations that some of these compounds exhibit exciting, cell-specific, anti-cancer potential (Tan et al., 2015). The foregoing suggests this is a fertile area of research, well deserving of continuing attention.

(I) Bis(N,N-diethyldithiocarbamato-κ 2 S,S′)(3-hydroxypyridine-κN)zinc
Crystal data [Zn(C 5  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.73 e Å −3 Δρ min = −0.45 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq

(II) Bis[N-(2-hydroxyethyl)-N-methyldithiocarbamato-κ 2 S,S′](3-hydroxypyridine-κN)zinc
Crystal data [Zn(C 4  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.43 e Å −3 Δρ min = −0.60 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq  (8)