Introduction

Polymorphism has been one of integral part of solid state supramolecular chemistry and polymorphism phenomenon is the last and most challenging hurdle for the success of designed synthesis of materials [1]. Various forms of polymorphism, including concomitant [2], packing [3], and conformational [4] have been studied as interesting phenomena in the solid-state sciences. The development of novel polymorphs of potential and existing drugs has for some time been a method for modifying and improving their physical properties [5]. The control of the process of nucleation and/or crystal growth at the beginning of crystallization from solvents is potential way for modifications of novel polymorphs across a range of industries involving dye [6], food stuff [7], drugs [8], and explosives [9]. The control of morphology and polymorphism is essential to achieve optimized molecular configurations and physical properties and to understand the structure–property relationships and design of new materials [10].

N,N-Diethylnicotinamide (dena) is a toxic agent, but coordinated in the form of complexes it shows different biological activity [11–16]. The coordination of the dena ligand occurs via the pyridine ring nitrogen atom and the other possible donor atoms for coordination bonds are less preferred. There are 60 structures of metal complexes containing the dena moiety bonded to a metal atom via the pyridine nitrogen donor atom and only nine of those structures contain dena as a bridging ligand bonded to the metal atom by carbonyl oxygen donor atoms too [17–25]. The monodentate bonding mode of the dena ligand is even more dominant for carboxylatocopper(II) complexes and there are two main stoichiometries within this group of complexes with the dena ligand. The 1:1 stoichiometry is found in paddle–wheel dinuclear complexes type [Cu2(RCOO)4(dena)2] [12, 26–28]. The most frequent 1:2 stoichiometry can be found in monomeric complexes of Cu(RCOO)2(dena)2(H2O) x , where x = 0, [29, 30], x = 2 [18, 31–35], or x = 4 [36], and in all those complexes the dena molecules are monodentate N donor ligands. Recently, the first two polymeric complexes with bridging dena molecules, of the composition [Cu2(RCOO)4(dena)1] n , have been structurally characterized [17, 18].

In this article, we report on the preparation and spectral properties, of six copper(II) complexes containing {Cu(X-sal)2(dena)2(H2O)2} core moiety (where X = 4-, 5-MeO and 3-, 4-, 5-Me), together with spectral data of [Cu(3-MeOsal)2(dena)2(H2O)2]∙2H2O that structure has been already published [36], but according to its structure it belongs to this group. For four of presented new complexes their X-ray structures are reported too.

Experimental

Materials and methods

Analytical grade (Aldrich, or Sigma) chemicals were used without further purification. Carbon, hydrogen, and nitrogen analyses were carried out on a CHNSO FlashEATM 1112 Automatic Elemental Analyzer. The copper content was determined by electrolysis of water solution obtained by the sample mineralization with a mixture of sulfuric acid and potassium peroxodisulfate.

The infrared spectra (4,000–400 cm−1) were measured with a NICOLET 5700 FT-IR (Nicolet) spectrophotometer at room temperature using ATR technique. The electronic spectra (190–1,100 nm) of the complexes were measured in Nujol suspension with a SPECORD 200 (Carl Zeiss Jena) spectrophotometer at room temperature. EPR spectra of the powdered samples were recorded at room temperature with a spectrometer Brucker ESP 300 operating at X-band equipped with an ER 035 Bruker NMR gaussmeter and HP 5350B Helwett Packard microwave frequency counter.

Syntheses of 1a

3-Methyl-salicylic acid (336 mg, 2.0 mmol) was by rinsing added to an aqueous solution of copper(II) acetate (10 mL, 1.0 mmol) with diethylnicotinamide (0.17 cm3, 2.0 mmol) under stirring and total volume of reaction mixture about 30 mL was reached. The reaction mixture was stirred at ambient temperature until the reaction finished. The product which precipitated was filtered off and mother liquid was left to crystallize at ambient temperature. The crystals suitable for X-ray structure determination were separated and dried at ambient temperature.

Cu(3-Mesal)2(dena)2(H2O)2 (1a): Yield: 0,41 g; 55%. Anal Calc.: C, 56.57; H, 6.11; N, 7.39. Found: C, 56.42; H, 5.86; N, 7.36.

Syntheses of 1b, 2–4

Appropriate methyl- or methoxy-salicylic acid (336 mg, 2.0 mmol for methoxysalicylic acid or 304 mg, 2.0 mmol for methylsalicylic acid) was under stirring added to the mixture of copper(II) acetate solution (1.0 mmol copper(II) acetate in 10 cm3 of water) with diethylnicotinamide (0.34 cm3, 2.0 mmol) and solvent added to obtain total volume of reaction mixture 200 cm3 for aqueous solutions or 30 cm3 for acetonitrile–water (1:1) ones. The reaction mixture was stirred at ambient temperature until the reaction finished. The products which precipitated (with exception of 3- and 5-methoxysalicylate, where no precipitation were observed) were filtered off and mother liquids were left to crystallize at ambient temperature. The crystals suitable for X-ray structure determination were separated and dried at ambient temperature.

Cu(3-Mesal)2(dena)2(H2O)2 (1b): Yield: 0,49 g; 65%. Anal Calc.: C, 56.57; H, 6.11; N, 7.39. Found: C, 56.34; H, 5.93; N, 7.12.

Cu(4-Mesal)2(dena)2(H2O)2 (2): Yield: 0,54 g; 71%. Anal Calc.: C, 56.57; H, 6.11; N, 7.39. Found: C, 56.24; H, 6.48; N, 7.44.

Cu(5-Mesal)2(dena)2(H2O)2 (3): Yield: 0,59 g; 77%. Anal Calc.: C, 56.57; H, 6.11; N, 7.39. Found: C, 57.07; H, 6.04; N, 7.36.

Cu(5-MeOsal)2(dena)2(H2O)2 (4): Anal Calc.: C, 54.71; H, 5.74; N, 7.26. Found: C, 54.72; H, 5.61; N, 7.06.

Cu(4-MeOsal)2(dena)2(H2O)2 (5): Yield: 0,45 g; 59%. Anal Calc.: C, 54.71; H, 5.74; N, 7.26. Found: C, 54.85; H, 6.06; N, 7.14.

X-ray crystallography

Crystal data and conditions of data collection and refinement are reported in Table 1. Data collection and cell refinement were carried out using Bruker-Nonius KappaCCD diffractometer [37, 38] at 150 K for (1a), Kuma KM-4 CCD diffractometer [39] at 100 K for (4, 5) or Siemens P4 diffractometer [40] at 293 K for (6) with graphite monochromated Mo Kα radiation. Data collection and cell refinement were carried out using Xcalibur PX CCD diffractometer [39] at 100 K for (1b) with graphite monochromated Cu Kα radiation. The diffraction intensities were corrected for Lorentz and polarization factors. The analytical absorption corrections [41] for (1b, 4 and 5 at 100 K) were made by using CrysAlis-RED [39]. The semi-empirical absorption corrections for 1a and 5 at 293 K were applied using the program SADABS [42] (multi-scan method) or the program XEMP [43] (psi-scan method). The structures were solved by direct methods using SHELXS-97 [44] or SIR-97 [45] and refined by the full-matrix least-squares procedure with SHELXL-97 [44]. Geometrical analyses were performed with SHELXL-97. The structures were drawn with XP in SHELXTL [44]. The remaining hydrogen atoms were positioned with O–H = 0.84 Å for hydroxyl and water atoms and C–H = 0.95, 0.98, and 0.99 Å for aromatic, methyl, and methylene hydrogen atoms, respectively, and constrained to ride on their parent atoms, with Uiso(H) = xUeq(C,O), where x = 1.5 for methyl, hydroxyl and water hydrogen atoms, and x = 1.2 for other hydrogen atoms. The positions of water hydrogen atoms were restrained by DFIX commands of SHELXL-97 and the refined positions have been constrained using AFIX 3 commands of SHELXL-97.

Table 1 Crystallographic data for compounds 1a, 1b, 4, and 5
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The powder samples 2 and 3 were measured with Bragg–Brentano diffractometer Philips PW 1730/1050, using ß-filtered Co Kα radiation, 40 kV/35 mA in the range of 3°–51° 2Θ, step 0.02°.

Results and discussion

The preferential ability of dena ligand to act as pyridine nitrogen donor has its consequence in domination of Cu(RCOO)2(dena)2(H2O) x (where x = 0, [29, 30], x = 2 [18, 31–35] or x = 4 [36]) stoichiometry. The observation of the green [Cu2(2-NO2bz)4(dena)1] n (2-NO2bz = 2-nitrobenzoate) polymeric complex formation at the beginning of the reactant reaction followed by its slow transformation into the blue [Cu(2-NO2bz)2(dena)2(H2O)2] in reaction mixture [18] was the reason why the preparation of the presented complexes were done also at different conditions (different dilution of reaction mixture, different solvents and temperature too). The most interesting feature of the realized experiments was observation of some new types of obtained products. As the first it should be mentioned the observation that despite the condition of synthesis changing the complex [Cu(3-MeOsal)2(dena)2(H2O)2]∙2H2O (6) [32] is the only product obtainable independently on the reaction conditions. The second note concerning the syntheses to be mentioned is that despite the great effort the X-ray suitable crystals of complexes [Cu(4-Mesal)2(dena)2(H2O)2] (2), and [Cu(5-Mesal)2(dena)2(H2O)2] (3) were not obtained thus only analytical and spectral characterization is presented bellow. The third and the last note to be given is that the complex [Cu(3-Mesal)2(dena)2(H2O)2] gives two different polymorphic forms 1a or 1b as the consequence of changing the course of synthesis (see “Experimental” section for details).

The principal structural features of complexes 1a, 1b, 4, and 5 are illustrated in Fig. 1. Selected bond distances, angles, and torsion angles of complexes 1a, 1b, 4, and 5 are given in Table 2. The structures of complexes 1a, 1b, 4, and 5 consist of centrosymmetric molecules with an elongated tetragonal–bipyramidal coordination polyhedron around the copper(II) atom. The coordination spheres of the all copper(II) atom are in the trans-equatorial planes formed by two carboxylate anions [3-methylsalicylate (1), 5-methoxysalicylate (4) or 4-methoxysalicylate (5)] bonded via O1 atoms [the Cu–O1 lengths are in the range 1.977(2)–1.988(2) Å] and two nitrogen donor atoms of pyridine rings of N,N-diethylnicotinamide [the Cu–N1 lengths are in the range 2.004(2)–2.020(2) Å]. The two axial positions of tetragonal–bipyramidal coordination environments are occupied by the two water molecules [the Cu–O1W distances are in the range 2.406(2)–2.458(2) Å], thus T parameter values [46] exhibit also very narrow values range [T = 0.81–0.83] suggesting very small and similar pattern of coordination polyhedron deformation. The water molecules of all complexes under study are due to the intramolecular hydrogen bonds [O1W–H1W···O2 with O1W···O2 distances in the region 2.702(4)–2.764(3) Å] (Table 3) slightly shifted from precise apical positions and the O1–Cu–O1W angles are in the region 90.97(8)–96.02(9)° and six-membered metalocycles are formed by those bonds. The hydroxyl and carboxylate groups of salicylate anions create additional six-membered intramolecular rings S(6) [47] through intramolecular hydrogen bonds O3–H3O···O2 with O3···O2 distances in the range 2.518(4)–2.562(3) Å. Similar coordination environment about copper atom has been observed in crystal structure of complex [Cu(3-MeOsal)2(dena)2(H2O)2]∙2H2O (6) [36] (Table 2) and other [Cu(RCOO)2(dena)2(H2O)2] complexes [18, 31–35].

Fig. 1
figure 1

Perspective view of [Cu(X-sal)2(dena)2(H2O)2], with the atom numbering scheme. The all thermal ellipsoids are drawn at the 30% probability level: a polymorph-I of complex [Cu(3-Mesal)2(dena)2(H2O)2] (1a); b polymorph-II of complex [Cu(3-Mesal)2(dena)2(H2O)2] (1b); c complex [Cu(5-MeOsal)2(dena)2(H2O)2] (4); d complex [Cu(4-MeOsal)2(dena)2(H2O)2] (5)

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Table 2 Selected bond distances (Å) and bond angles (°) for 1a, 1b, 4, 5, and 6
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Table 3 Selected parameters of hydrogen bonds (Å, °) for 1a, 1b, 4, and 5
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All presented structures 1a, 1b, 4, and 5 exhibit similar orientation of pyridine ring in relation to equatorial plane of their coordination polyhedra and dihedral angle between pyridine ring plane and coordination polyhedron N1–O1–Cu–O1′–N1′ equatorial plane is within very narrow interval of 38.9–42.5° [39.06 for 1a, 37.01 for 1b, 42.52 for 4, 38.86 for 5 at 100 K, or 38.07 for 5 at 293 K]. The carboxamide groups N2–C14–O4 are also turned away from the pyridine ring plane by 45.4–70.5° [50.07 for 1a, 55.81 for 1b, 45.35 for 4, 66.48 for 5 at 100 K, 70.51 for 5 at 293 K, or 58.28 for 6] and the carboxamide groups are nearly perpendicular (68.8–89.3°) to coordination polyhedron equatorial plane [71.50 for 1a, 73.57 for 1b, 68.79 for 4, 88.10 for 5 at 100 K, or 89.30 for 5 at 293 K]. The most interesting feature of such carboxamide plane orientation is that there are two possible orientations of the O4–C14 or N2–C14 bonds. One of them is roughly perpendicular to coordination polyhedron z-axis (Scheme 1), it could be called as equatorial orientation, and the other one is nearly parallel with z-axis, so called axial orientation, similarly as it is used for the cyclohexane hydrogen atom positions. The 1a and 4 (Fig. 1a, c) exhibit C14=O4 bond oriented perpendicularly to Cu–OH2 bonds in equatorial C14=O4 bond orientation, while in complexes 1b and 5 (Fig. 1b, d) the C14=O4 bonds are oriented about alongside the z-axis (axial C14=O4 bond). This is interesting especially for the pair of complexes 1a and 1b, which are two isomers of the same composition [Cu(3-Mesal)2(dena)2(H2O)2] so it can be concluded that 1a and 1b exist as two conformation polymorphs [48], which are simultaneously supramolecular isomers [49–51] too.

Scheme 1
scheme 1

Schematic drawing of two possible orientation of the carboxamide group in relation to part of coordination polyhedron

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Exactly the N,N-diethylcarboxamide groups of N,N-diethylnicotinamide ligand two orientations, could be expressed by torsion angles C9–C10–C14–N4 and C9–C10–C14–O4 (Table 2). The polymorph 1a of complex [Cu(3-Mesal)2(dena)2(H2O)2] (Fig. 1a) and complex [Cu(5-MeOsal)2(dena)2(H2O)2] (4) (Fig. 1b) have equatorial C=O bond of the N,N-diethylcarboxamide group orientations thus C9–C10–C14–N4 torsion angle are −52.9(4) and −46.9(3)°, respectively, and C9–C10–C14–O4 torsion angles are 126.4(3) and 131.5(2)°, respectively. On the other hand the other polymorph 1b of the complex [Cu(3-Mesal)2(dena)2(H2O)2] (Fig. 1b) and complex [Cu(4-MeOsal)2(dena)2(H2O)2] (5) (Fig. 1d) have the C=O bond in axial orientation and the C9–C10–C14–N4 torsion angle are −124.7(3)° and −117.1(3)°, respectively, and C9–C10–C14–O4 torsion angles are 52.0(4)° and 63.3(4)°, respectively (the torsion angles of 5 at room temperature are given only in Table 2). The other differences among orientations of ethyl groups of N,N-diethylnicotinamide ligands are too observed in torsion angles C14–N2–C15–C16 and C14–N2–C17–C18 (Table 2). On the other hand more understandable exact parameter to evaluate position of C14=O4 bond in relation to coordination polyhedron is quasi-torsion angle defined by O1W–Cu···C14–O4 atoms that is 20.20 for 1a, 4.45 for 1b, 13.39 for 4, and 5.77° for 5.

Supramolecular isomerism of the polymorphs is determined by this orientations of C14=O4 relative to polyhedron z-axis. The molecules of polymorph 1a (Fig. 2a) and complex 4 are linked by intermolecular hydrogen bonds between hydrogen atoms of water ligands and carboxamide oxygen atoms of N,N-diethylnicotinamide ligands of adjacent molecules O1W–H2W···O4ii [Symmetry code: (ii) x + 1, y, z] with O1W···O4ii interatomic distance of 2.811(3) and 2.751(2) Å, respectively (Table 3) through \( R_{2}^{2} \)(16) rings [47], and π–π stacking interactions [52] between two symmetrically adjacent pyridine rings N1/C9–C13 [Symmetry code: (iv) −x, −y + 1, −z + 1] of N,N-diethylnicotinamide molecules (Fig. 2a), [centroid···centroid distances are 3.87 and 3.65 Å, respectively] into chain in direction [100] (Fig. 2a). The distances between two π–π stacked planes are exactly 3.55 and 3.58 Å, respectively, and the Cu···Cu distances within the chains are 8.637 and 8.347 Å for complex 1a and 4, respectively.

Fig. 2
figure 2

Crystal packing of two supramolecular isomers of [Cu(3-Mesal)2(dena)2(H2O)2], the salicylate anions are omitted for clarity: a 1-D Supramolecular band chain of 1a through O–H···O hydrogen bonds in [100] axis, the π–π interactions between pyridine rings are inside supramolecular band chain; b 1-D Supramolecular band chain of 1b through O–H···O hydrogen bonds in [1ī0] axis. c The the π–π interactions between pyridine rings of 1b are between two supramolecular band chains

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The molecules of the other polymorph 1b (Fig. 2b) as well as complex 5 are too joined by intermolecular hydrogen bonds between hydrogen atoms of water ligands and amide oxygen atoms of N,N-diethylnicotinamide ligands of adjacent molecules through \( R_{2}^{2} \)(16) rings [47], but the orientation of pyridine rings do not allow π–π stacking interactions within the supramolecular the chains. The supramolecular chains are due to the different orientation of the C14=O4 oriented in direction [1ī0] (Fig. 2b) and the hydrogen bond O1W–H2W···O4iii [Symmetry code: (ii) x + 1, y, z] are O1W···O4iii interatomic distance of 2.808(3) and 2.835(3) Å, respectively (Table 3). The different chain orientation and their different packing of the 1a or 4 molecules result in different Cu···Cu distances within the bands are 9.612 and 9.918 Å for complex 1b and 5, respectively. The π–π stacking interactions [52] between two pyridine aromatic rings of N,N-diethylnicotinamide ligands of two neighboring [Symmetry code: (v) −x + 1, −y + 2, −z + 1] complex molecules are localized between two supramolecular chains (Fig. 2c). The centroid···centroid distances are 3.52 and 3.65 Å, respectively, and the distances between two planes of pyridine rings are exactly 3.55 and 3.58 Å, respectively. It could be concluded that this pair of complexes (1b and 5) and the previous pair (1a and 4) represents two supramolecular isomers that differ by the Cu···Cu distance within the chain, by orientation of the chains in crystal structure and finally in some differences in π–π stacking interactions.

The supramolecular chains with additional the π–π stacking interactions similar to the last couple of the supramolecular isomers have been observed in crystal structures of complexes [Cu(RCOO)2(dena)2(H2O)2], where RCOO is 2-chloronicotinate [34] or 4-nitrobenzoate [35], but if RCOO− anion is more bulky fenamate, the additional π–π stacking interactions have been not observed [31–33]. The crystal structure of complex [Cu(RCOO)2(dena)2(H2O)2], where RCOO− is 2-nitrobenzoate present alternative supramolecular organization of complex molecules in two-dimensional hydrogen bonds network, the molecules are linked through hydrogen bonds between water ligands and carboxamide oxygen atom of N,N-diethylnicotinamide molecules [18]. Finally, the crystal structure of complex [Cu(3-MeOsal)2(dena)2(H2O)2]∙2H2O (6) presents enriched hydrogen bonds network, where hydroxyl and methoxy groups of 3-methoxysalicylate anions are specifically acceptor of hydrogen bonds and uncoordinated additional water molecules are donors of hydrogen bonds [36], which are presented by creating ring R 21 (5) [47]. These changes are partially seen in similar orientation of pyridine ring in relation to equatorial plane of the coordination polyhedra, but the dihedral angle between pyridine ring plane and coordination polyhedron equatorial plane is significantly smaller, about 29°. The dihedral angle of carboxamide plane to pyridine ring one is about 73° for 6. It should be pointed out that C=O bond is axially oriented in relation to coordination polyhedron z axis.

The infrared spectra were recorded for all complex series. The carboxylate stretching frequencies νas(COO−) and νs(COO−) for each of the complexes under study are in the regions at about 1,620 and 1,420 cm−1, respectively, and are given in Table 4. Differences between antisymmetric and symmetric stretches (Δν = νas − νs) are for all prepared complexes greater than Δν for the ionic form, that is consistent with bonding mode of carboxylate group [53, 54] proved by X-ray analysis. The differences in position of the ν(COO−) stretching frequencies of the individual complexes are very small and that is in good agreement with very small differences in bonding of the salicylate in copper(II) coordination sphere. Similarly, the characteristic frequencies of dena ligand (e.g. ν(CN) of pyridine ring) are due to very small differences in Cu–N1 distances found at the same positions for all studied complexes. More information could be found in the shape and intensity of bands in the region of 3,500–3,250 cm−1, which could be attributed to O–H vibrations of coordinated ligands typical for complexes of the stoichiometry [Cu(RCOO)2(dena)2(H2O)2]. Different shape of the spectra of complexes 1a and 1b (Fig. 3) led us to conclusion to study the X-ray structure of both complexes. It could be concluded that this spectra region could taken as the proof of existence of polymorphic form. Moreover, this region of O–H vibrations exhibits different pattern for complex [Cu(3-MeOsal)2(dena)2(H2O)2]·2H2O—there is also an additional sharp and stronger absorption band at 3,547 cm−1.

Table 4 Wavenumbers (cm−1) of the COO− stretches, solid-state electronic spectra (nm) and g values for the copper(II) complexes
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Fig. 3
figure 3

Comparison of infrared spectra of both polymorphs [Cu(3-Mesal)2(dena)2(H2O)2]

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The electronic spectra of the discussed complexes in solid showed a typical feature of tetragonal bipyramidal arrangement around Cu(II) [55]. The broad asymmetric ligand field band with a maximum in the range of 660–640 nm (Table 4) is attributed to d ← d transition and very small differences in shape and in the maximum position are in good agreement with above mentioned differences of CuN2O2O’2 chromophores. There are also intraligand charge transfer bands (250–300 nm) and LMCT band in the range of 300–350 nm.

The EPR spectra signals (Fig. 4) of powdered samples measured at room temperature reflect of the axial symmetry of the complexes. The simulation of spectra gave us the g-parameter values (Table 4) in the range of 2.07–2.08 for g⊥ and 2.31–2.33 for g ‖, respectively. The axial symmetry and obtained g values are consistent with tetragonal bipyramidal symmetry of copper(II) environment [56], as well as with above mentioned differences of CuN2O2O′2 chromophores. The obtained G parameter [57] values (Table 4) are in all mentioned complexes within the narrow range and they are close to G = 4 and that could be taken as consistent with small axial distortion of coordination polyhedra and with their small differences when comparing all studied complexes. So the EPR spectra of measured samples are very similar and do not allow differentiate conformational isomers one from the other.

Fig. 4
figure 4

EPR spectra of powdered sample of 2 (dark line measured at room temperature, and dashed line simulated)

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The above mentioned problems with using spectral methods for identification of the orientation of the C=O carboxamide bond relative to coordination polyhedron axis led us to analysis of crystallographic data and they clearly confirmed that both groups showing similar C=O bond orientation exhibit significantly different basic unit cell parameters. So the X-ray diffraction pattern of powdered samples 2 and 3 were compared with calculated X-ray diffraction pattern of complexes with known structure and that gave us the evidence that the samples of prepared complexes exhibit structures similar to complexes 1b, or 5. Finally indexing [58] of powder diffraction patterns and calculation of basic unit cell parameters (Table 5) clearly confirm this conclusion.

Table 5 Crystallographic data for compounds 2 and 3 from powder samples
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The melting point determination has shown that all studied complexes undergo some changes between 95 and 105 °C associated with small color intensification to darker blue color that could be attributed to the dehydration reactions [59, 60]. The further heating of samples up to 220 °C were not associated with any observable changes thus it could be concluded that dehydrated samples decompose over this temperature.

Conclusions

In this study, we present the results on structural and spectroscopic properties of a series of five new monomeric 3-, 4-, 5- methylsalicylatocopper(II), or 4- and 5-methoxysalicylatocopper(II) complexes with N,N-diethylnicotinamide as monodentate terminal ligand. This study has shown that N,N-diethylnicotinamide in these complexes prefer monomeric structure of formula [Cu(Me(O)sal)2(dena)2(H2O)2]. The complex molecules are linked to supramolecular chains through hydrogen bonds, which can exist in two alternative configurations. The [Cu(3-Mesal)2(dena)2(H2O)2] complex exist in both configuration forms and it present the example of conformation polymorphs and it could be taken as the supramolecular isomers existence.

Supplementary data

Crystallographic data (excluding structure factors) for the structure reported in this article have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC-773722–773726. Copies of the data can be obtained free of charge on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: (internat.) +44 1223/336033; e-mail:deposit@ccdc.cam.ac.uk].