Crystal structures of two CuII compounds: catena-poly[[chloridocopper(II)]-μ-N-[ethoxy(pyridin-2-yl)methylidene]-N′-[oxido(pyridin-3-yl)methylidene]hydrazine-κ4 N,N′,O:N′′] and di-μ-chlorido-1:4κ2 Cl:Cl-2:3κ2 Cl:Cl-dichlorido-2κCl,4κCl-bis[μ3-ethoxy(pyridin-2-yl)methanolato-1:2:3κ3 O:N,O:O;1:3:4κ3 O:O:N,O]bis[μ2-ethoxy(pyridin-2-yl)methanolato-1:2κ3 N,O:O;3:4κ3 N,O:O]tetracopper(II)

A linear polymeric CuII complex and a CuII open-cube complex were synthesized using the tridentate Schiff base ligand, {1-[1-(pyridyl)(2-ethoxyethylidene)]-2-[(pyridin-3-yl)carbonyl]}hydrazine and copper(II) acetate and their molecular and crystal structures determined.

Two Cu II complexes [Cu(C 14 H 13 N 4 O 2 )Cl] n , I, and [Cu 4 (C 8 H 10 NO 2 ) 4 Cl 4 ] n , II, have been synthesized. In the structure of the mononuclear complex I, each ligand is coordinated to two metal centers. The basal plane around the Cu II cation is formed by one chloride anion, one oxygen atom, one imino and one pyridine nitrogen atom. The apical position of the distorted square-pyramidal geometry is occupied by a pyridine nitrogen atom from a neighbouring unit, leading to infinite one-dimensional polymeric chains along the b-axis direction. Each chain is connected to adjacent chains by intermolecular C-HÁ Á ÁO and C-HÁ Á ÁCl interactions, leading to a three-dimensional network structure. The tetranuclear complex II lies about a crystallographic inversion centre and has one core in which two Cu II metal centers are mutually interconnected via two enolato oxygen atoms while the other two Cu II cations are linked by a chloride anion and an enolato oxygen. An open-cube structure is generated in which the two open-cube units, with seven vertices each, share a side composed of two Cu II ions bridged by two enolato oxygen atoms acting in a 3 -mode. The Cu II atoms in each of the two CuO 3 NCl units are connected by one 2 -O and two 3 -O atoms from deprotonated hydroxyl groups and one chloride anion to the three other Cu II centres. Each of the pentacoordinated Cu II cations has a distorted NO 3 Cl square-pyramidal environment. The Cu II atoms in each of the two CuO 2 NCl 2 units are connected by 2 -O and 3 -O atoms from deprotonated alcohol hydroxy groups and one chloride anion to two other Cu II ions. Each of the pentacoordinated Cu II cations has a distorted NO 2 Cl 2 square-pyramidal environment. In the crystal, a series of intramolecular C-HÁ Á ÁO and C-HÁ Á ÁCl hydrogen bonds are observed in each tetranuclear monomeric unit, which is connected to four tetranuclear monomeric units by intermolecular C-HÁ Á ÁO hydrogen bonds, thus forming a planar two-dimensional structure in the (101) plane.

Chemical context
Picolinic acid esters (Gonzá lez- Duarte et al., 1996Duarte et al., , 1998Hay & Clark, 1979;Luo et al., 2002;Paul et al., 1974) as well as ISSN 2056-9890 nicotinic acid hydrazide (Bharati et al., 2015;Galić et al., 2011;Nakanishi & Sato, 2017) are widely used in coordination chemistry for their ability to bind metals through the amino and/or the ester functional groups (Hay & Clark, 1979). Complexes formed by ethyl picolinate (EP) with various divalent metal thiocyanates (Paul et al., 1975), chlorides (Gonzá lez-Duarte et al., 1996) and perchlorates (Natun et al., 1995) have been prepared and characterized. Several modes of coordination are observed, depending on the conformation of the molecule. Ethyl picolinate acts as a bidentate ligand coordinating through the ring nitrogen and the carbonyl oxygen. The carboxylic ester function can coordinate in several ways, while the pyridine nitrogen atom can also coordinate in a unidentate fashion. The nicotinic acid hydrazide can coordinate through the hydrazino moiety as well as through the pyridine nitrogen atom (Lumme et al., 1984;Shahverdizadeh et al., 2011a,b). These facts make these ligands and their analogues very attractive and they have been used in several studies. Many polynuclear complexes of transition metals with various structures can be generated, depending on the disposition of the metal ions and the donor sites (N or O). Trimers (Zhang et al., 2009), square shapes (Aouaidjia et al., 2017), cyclic forms (Acevedo-Chá vez et al., 2002) and cubans (Shit et al., 2013) have been reported that have potential applications in the field of magnetism (Shit et al., 2013), catalysis (Okeke et al., 2018) and biomimetic synthesis (Wu et al., 2004). By extension, the introduction of an ethoxy-carbonyl group in the ortho position of the pyridine gives a ligand that can have a similar behavior to -amino acid esters. It has been shown that the presence of metal ions promotes the hydrolysis of the ester function of the picolinic ester (Xue et al., 2016). A condensation can then occur between nicotinic acid hydrazide and the hydrolysed picolinic ester, to generate two organic ligands with a large number of coordination sites in situ, in the presence of copper(II) ions. These ligands then coordinate to the copper(II) cations to yield the two complexes that are reported here.

Structural commentary
The condensation reaction of pyridine-2-carbaldehyde and nicotinic acid hydrazide in ethanol in the presence of copper acetate yields two different complexes whose ligands are respectively a hemiacetal [ethoxy(pyridine-2-yl)methanol] and a condensation product [({1-[1-ethoxy-1-(pyridin-2-yl)methylene]}-2-(oxonicotinyl))hydrazine]. It has been shown (Papaefstathiou et al., 2000;Boudalis et al., 2008;Mautner et al., 2010) that the presence of a metal can induce a nucleophilic attack of the ethanol molecule on the carbonyl group to give a hemiacetal. This reaction can also occur when a fragment such as a pyridyl nitrogen atom is present that is capable of inducing the polarization of the carbonyl function (Papaefstathiou et al., 2000). It is under these conditions that the complexes I and II were formed in situ.
In the crystal structure of the coordination polymer [CuCl(C 14 H 13 N 4 O 2 )] n , I, the repeat unit of which is shown in (Fig. 1), the Cu II center is pentacoordinated by one chloride atom, one enolate oxygen atom of the mono deprotonated organic ligand, one pyridine, one imino nitrogen atom, and by a pyridine nitrogen atom of a ligand from an adjacent complex An ORTEP view of the repeat unit of the coordination polymer I, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: (i) 3 2 À x, À 1 2 + y, 3 2 À z; (ii) molecule. This latter contact bridges the Cu II cations to form a one-dimensional coordination polymer along the b-axis direction (Fig. 2). Intermolecular C-HÁ Á ÁO and C-HÁ Á ÁCl hydrogen bonds, (Table 1), link the polymers into a threedimensional network (Fig. 3). The coordination environment can be best described as strongly distorted square pyramidal. The basal plane around the Cu II ion is formed by the Cl2 anion with a Cu1-Cl2 distance of 2.2707 (6) Å , an O16 atom with a Cu1-O16 distance of 1.9808 (15) Å and the N11 and N22 atoms from the same ligand with a Cu-N distances of 1.9437 (17) and 2.0444 (17) Å (Table 2). These bond lengths are similar to the values found in related complexes (Datta et al., 2011a,b;Da Silva et al., 2013). The apical position of the distorted square pyramid is occupied by one pyridine N3 atom of a neighbouring unit with a Cu-N distance of 2.2009 (17) Å . This distance is shorter than that found in similar compound (Roztocki et al., 2015). The ligand, which acts in a tridentate fashion, forms two five-membered rings upon coordination with the Cu II centre: OCNNCu and NCCNCu, with the N11 atom common to both. The five-membered chelate rings impose large distortions on the ideal angles of a regular square pyramid, with bite angles in the range 79.11 (7)-79.40 (7) , which are slightly smaller than those found in similar compounds (Roztocki et al., 2015). The transoid angles in the basal plane O16-Cu1-N22 and N11-Cu1-Cl2 deviate severely from linearity with values of 158.51 (7) and 146.17 (6) ( Table 2). These two largest angles around the Cu II ion give a parameter of 0.206, which is indicative of a distorted square-pyramidal environment around the Cu II ion (Addison et al., 1984). The polymer expansion of complex I, showing an infinite chain propagating along the b-axis direction. In this and subsequent figures, hydrogen bonds are drawn as dashed lines. Table 1 Hydrogen-bond geometry (Å , ) for I. Symmetry codes: (ii) Àx þ 3 2 ; y þ 1 2 ; Àz þ 3 2 ; (iii) Àx þ 1 2 ; y À 1 2 ; Àz þ 3 2 ; (iv) Àx þ 1; Ày þ 1; Àz þ 1.

Figure 3
A view of the crystal packing of complex I.

Figure 4
The structure of II with ellipsoids drawn at the 50% probability level. Unlabelled atoms are generated by the symmetry operation 1 À x, 1 À y, 1 À z.

Supramolecular features
The crystal structure of I is determined by a coordination synthon in which each ligand is coordinated to two metal centers, giving rise to infinite one-dimensional polymeric chains along the b-axis direction (Fig. 2). Adjacent chains are linked to one another by intermolecular C-HÁ Á ÁO and C-HÁ Á ÁCl hydrogen bonds (Table 1), leading to a three-dimensional network structure (Fig. 3). In the crystal structure of II, C18-H18Á Á ÁO23 hydrogen bonds link the complex molecules into chains along the bc diagonal (Fig. 6). Additional C18-H18Á Á ÁO23 contacts generate two-dimensional sheets of molecules also along the bc diagonal (Fig. 7). --stacking interactions occur between the two unique N10/C5-C9 and N21/C16-C20 pyridine rings with a centroid-to-centroid separation of 3.6800 (16) Å (symmetry operation 3 2 À x, À 1 2 + y, 3 2 À z). These contacts combine with the C-HÁ Á ÁO hydrogen bonds to stack the molecules in a three-dimensional network along the a-axis direction (Fig. 8).

Synthesis and crystallization
To a solution of 2-pyridine carbaldehyde (0.1070 g, 1 mmol) in 30 ml of ethanol was added a solution of nicotinic hydrazide (0.1371 g, 1 mmol) in 10 ml of ethanol. The mixture was stirred for 5 min. A solution of Cu(OOCH 3 ) 2 ÁH 2 O (0.1996 g, 1 mmol) in 5 ml of ethanol was added at room temperature. The initial yellow solution immediately turned deep blue and was stirred under reflux for 2 h. The mixture was filtered and the solution evaporated to near dryness. The solid was isolated by filtration and recrystallized from a minimum of ethanol. On standing for five days, two types of crystals suitable for X-ray analysis were formed, light-yellow blocks of I and light-green plates of II. Chains of molecules of II along the bc diagonal.

Figure 7
Two-dimensional sheet of molecules of II along the bc diagonal.

yl)methylidene]hydrazine-κ 4 N,N′,O:N′′] (I)
Crystal data [Cu(C 14  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.