Cu II Complexes and Coordination Polymers with Pyridine or Pyrazine Amides and Amino Benzamides—Structures and EPR Patterns

: Isonicotine amide, picoline amide, pyrazine 2-amide, 2- and 4-amino benzamides and various Cu II salts were used to target Cu II complexes of these ligands alongside with 1D and 2D coordination polymers. Under the criterion of obtaining crystalline and single phased materials a number of new compounds were reliably reproduced. Remarkably, for some of these compounds the ideal Cu:ligand ratio of the starting materials turned out to be very di ﬀ erent from Cu:ligand ratio in the products. Crystal and molecular structures from single-crystal XRD were obtained for all new compounds; phase purity was checked using powder XRD. We observed exclusively the O amide and not the N H 2amide function binding to Cu II . In most of the cases; this occurred in chelates with the second pyridine, pyrazine or aminophenyl N function. µ - O , N ditopic bridging was frequently observed for the N = pyridine, pyrazine or aminophenyl functions, but not exclusively. The geometry around Cu II in these compounds was very often axially elongated octahedral or square pyramidal. X-band EPR spectra of powder samples revealed various spectral symmetry patterns ranging from axial over rhombic to inverse axial. Although the EPR spectra cannot be unequivocally correlated to the observed geometry of Cu II in the solid state structures, the EPR patterns can help to support assumed structures as shown for the compound [Cu(Ina) 2 Br 2 ] (Ina = isonicotine amide). As UV-vis absorption spectroscopy and magnetic measurement in the solid can also be roughly correlated to the surrounding of Cu II , we suggest the combination of EPR, UV-vis spectroscopy and magnetic measurements to elucidate possible structures of Cu II compounds with such ligands.


Introduction
Pyridine carboxamides, pyrazine carboxamides and amino-benzamides (Scheme 1) are interesting ditopic ligands for Cu II coordination chemistry . One reason is their use as versatile building blocks in coordination polymers and MOFs for various applications [1][2][3]8,9,[11][12][13]16,20,21,26,27]. Another important reason is the biological relevance of some of the ligands used in this study (Scheme 1) [4][5][6]17,18,24,33]. An interesting general aspect of these ligands is the preference of Cu II to the different (offered) donor atoms in the ligands. From the viewpoint of the HSAB principle the N atom of the heteroaromatic cores is softer than the amine function of 4-amino benzamide and both are softer than the O amide function of amides or corresponding carboxylates. From the viewpoint of Cu metalloenzymes the frequent binding of soft ligands such as histidine-N and cysteine-S confirms the

Synthesis of the Cu Complexes
In a first series of experiments Cu II salts were reacted with the ligands shown in Scheme 1 in a Cu:ligand ratio of 1:1 in EtOH. Single crystals of 18 compounds were obtained by slow evaporation of the solvent from the reaction mixtures (Table 1). The Cu:ligand ratios were found ranging from 1:1 to 1:4. Coligands to Cu II were the anions from the Cu sources: Cl − , Br − , NO3 − , BF4 − , Tfa − , EtOH and H2O. ClO4 − was not coordinating but found as a counter ion. None of the ligands was found deprotonated in the structures. However, pyrazine-2-carboxamide was converted into pyrazine Scheme 1. Protoligands (ligand precursor prior to deprotonation) with abbreviations used in this study. In red: acidic protons.
Herein we report on a study aiming to explore the binding preferences of isonicotinamide (Ina), picolinamide (Pia), pyrazine-2-carboxamide (Pya) and 2-and 4-amino-benzamides (2-and 4-Aba; Scheme 1) towards Cu II . We also added the versatile ligand thio-bisacetamide (Tba) to this study, as Tba represents the aliphatic amides and we expected that the ligand will form SˆO or SˆN chelates. The ligands were reacted with various Cu II salts in EtOH without addition of bases to avoid deprotonation of the ligands. The compounds produced were studied in the solid state by single crystal and powder X-ray diffraction, EPR, magnetic measurements and UV-vis absorption spectroscopy. Being aware of the problem that our so-called "combinatorial approach"-which means dissolving metal salts and ligands and crystallising materials out of the mixture-might lead to a plethora of different structures, we aimed to work out reliable procedures for the preparation of defined structures which also allow reproducing the materials. We succeeded in doing so in many cases, and powder X-ray diffraction (PXRD) was used to evaluate the preparation methods and to prove the phase purity of the compounds. This also means that non-crystalline materials and materials which obviously contained mixtures of compounds as could be seen from their colours, which were obtained from further reactions of the seven ligands and the Cu salts, were not further analysed. Interestingly, this comprises all trials using nicotinamide as ligand.
Special focus was also laid on EPR spectroscopy of these solids. Having so many new structures and EPR data in hand we were able to correlate details in the EPR spectra such as spectral symmetry and g values to the local environment of the Cu II centres. Magnetic and UV-vis absorption data of selected samples were also recorded.

Synthesis of the Cu Complexes
In a first series of experiments Cu II salts were reacted with the ligands shown in Scheme 1 in a Cu:ligand ratio of 1:1 in EtOH. Single crystals of 18 compounds were obtained by slow evaporation of the solvent from the reaction mixtures (Table 1). The Cu:ligand ratios were found ranging from 1:1 to 1:4. Coligands to Cu II were the anions from the Cu sources: Cl − , Br − , NO 3 2 Br 2 ] (5) through grinding with KBr. Unfortunately, the obtained crystals of this compound were of poor quality preventing a structure solution. In a previous report of (5) space group P2 1 /c (No. 14) was concluded from 24 reflections by powder XRD and the authors assumed a polymeric structure with a distorted octahedral coordination around Cu II [39]. From the new compound [Cu(Ina) 4 [16]. e Reported previously, [16]. f No valid structure refinement possible; previous assignment from powder XRD = P2 1 /c (No. 14), from [22]. g A refinement in the standard space group P2 1 /c was not successful. h The structure could not be fully refined: The nitrate anions around the N2 (coordinating) and N3 (non-coordinating) atoms show systematic disorder due to symmetric alternation. For the coordinating N2-nitrate there are two possible symmetric identical positions to bridge between the two Cu1 ions, both with an occupation of 0.5. This leads to two nitrate anions in very close proximity in the cell, but must be understood as alternating motif in consecutive cells. The non-coordinating nitrate N3 atom shows similar disorder (for details, see Tables S30 and S31).
In a further series of experiments, we tried to reproduce the obtained compounds and optimise their yields. Cl and Br turned out to be very strong ligands to Cu II compared with the amides and we avoided them in these experiments. Similar observations that Cu-halide bonding dominates the structures of heteroleptic halide pyridine-amide Cu II complexes were reported before [3,5,[25][26][27]38,40]. Using the same reaction protocol but varying the Cu:ligand ratio, 10 out of these 18 compounds could be reliably reproduced in good to excellent yields and high phase purity as confirmed through elemental analyses and powder XRD (Scheme 2). In turn, this means that the compounds 2, 4, 11, and 14 remained unreproducible. avoided them in these experiments. Similar observations that Cu-halide bonding dominates the structures of heteroleptic halide pyridine-amide Cu II complexes were reported before [3,5,[25][26][27]38,40]. Using the same reaction protocol but varying the Cu:ligand ratio, 10 out of these 18 compounds could be reliably reproduced in good to excellent yields and high phase purity as confirmed through elemental analyses and powder XRD (Scheme 2). In turn, this means that the compounds 2, 4, 11, and 14 remained unreproducible.

Scheme 2.
Results of reproduction and optimisation reactions with yields and purities decreasing along the colour series: . Yields were defined relative to the ligands (for details, see Experimental Section).
For other compounds, the optimum ratio lies more to the Cu side with the most remarkable example being [Cu(Ina)4(H2O)2](BF4)2 (1) for which a 2:1 = Cu:ligand ratio was best to observe phase pure material, while a 1:4 ratio prevails in the compound. The most important parameter for the assessment of the synthesis was the phase purity. The second important parameter was the yield. However, it is important to note, that yields were either calculated based on Cu or based on the ligand. For example, for compound (1) a 2:1 ratio in the starting material meant a high yield relative to the ligand (88%) but, of course, a very low yield relative to the starting Cu II precursor (22%).

Scheme 2.
Results of reproduction and optimisation reactions with yields and purities decreasing along the colour series: avoided them in these experiments. Similar observations that Cu-halide bonding dominates the structures of heteroleptic halide pyridine-amide Cu II complexes were reported before [3,5,[25][26][27]38,40]. Using the same reaction protocol but varying the Cu:ligand ratio, 10 out of these 18 compounds could be reliably reproduced in good to excellent yields and high phase purity as confirmed through elemental analyses and powder XRD (Scheme 2). In turn, this means that the compounds 2, 4, 11, and 14 remained unreproducible.

Scheme 2.
Results of reproduction and optimisation reactions with yields and purities decreasing along the colour series: . Yields were defined relative to the ligands (for details, see Experimental Section).
For other compounds, the optimum ratio lies more to the Cu side with the most remarkable example being [Cu(Ina)4(H2O)2](BF4)2 (1) for which a 2:1 = Cu:ligand ratio was best to observe phase pure material, while a 1:4 ratio prevails in the compound. The most important parameter for the assessment of the synthesis was the phase purity. The second important parameter was the yield. However, it is important to note, that yields were either calculated based on Cu or based on the ligand. For example, for compound (1) a 2:1 ratio in the starting material meant a high yield relative to the ligand (88%) but, of course, a very low yield relative to the starting Cu II precursor (22%).
IR spectroscopy allowed revealing some structural features of the compounds (data in the Experimental Section). The presence of BF4 − , ClO4 − , and NO3 − in the compounds as ligands or as counter anions is easily detectable through their characteristic vibrational modes. On the other hand, the data did not unequivocally allow determining whether these anions are ligands or counter ions. avoided them in these experiments. Similar observations that Cu-halide bonding dominates the structures of heteroleptic halide pyridine-amide Cu II complexes were reported before [3,5,[25][26][27]38,40]. Using the same reaction protocol but varying the Cu:ligand ratio, 10 out of these 18 compounds could be reliably reproduced in good to excellent yields and high phase purity as confirmed through elemental analyses and powder XRD (Scheme 2). In turn, this means that the compounds 2, 4, 11, and 14 remained unreproducible. For other compounds, the optimum ratio lies more to the Cu side with the most remarkable example being [Cu(Ina)4(H2O)2](BF4)2 (1) for which a 2:1 = Cu:ligand ratio was best to observe phase pure material, while a 1:4 ratio prevails in the compound. The most important parameter for the assessment of the synthesis was the phase purity. The second important parameter was the yield. However, it is important to note, that yields were either calculated based on Cu or based on the ligand. For example, for compound (1) a 2:1 ratio in the starting material meant a high yield relative to the ligand (88%) but, of course, a very low yield relative to the starting Cu II precursor (22%).
IR spectroscopy allowed revealing some structural features of the compounds (data in the Experimental Section). The presence of BF4 − , ClO4 − , and NO3 − in the compounds as ligands or as counter anions is easily detectable through their characteristic vibrational modes. On the other hand, the data did not unequivocally allow determining whether these anions are ligands or counter ions. avoided them in these experiments. Similar observations that Cu-halide bonding dominates the structures of heteroleptic halide pyridine-amide Cu II complexes were reported before [3,5,[25][26][27]38,40]. Using the same reaction protocol but varying the Cu:ligand ratio, 10 out of these 18 compounds could be reliably reproduced in good to excellent yields and high phase purity as confirmed through elemental analyses and powder XRD (Scheme 2). In turn, this means that the compounds 2, 4, 11, and 14 remained unreproducible. For other compounds, the optimum ratio lies more to the Cu side with the most remarkable example being [Cu(Ina)4(H2O)2](BF4)2 (1) for which a 2:1 = Cu:ligand ratio was best to observe phase pure material, while a 1:4 ratio prevails in the compound. The most important parameter for the assessment of the synthesis was the phase purity. The second important parameter was the yield. However, it is important to note, that yields were either calculated based on Cu or based on the ligand. For example, for compound (1) a 2:1 ratio in the starting material meant a high yield relative to the ligand (88%) but, of course, a very low yield relative to the starting Cu II precursor (22%).
IR spectroscopy allowed revealing some structural features of the compounds (data in the Experimental Section). The presence of BF4 − , ClO4 − , and NO3 − in the compounds as ligands or as counter anions is easily detectable through their characteristic vibrational modes. On the other hand, the data did not unequivocally allow determining whether these anions are ligands or counter ions. avoided them in these experiments. Similar observations that Cu-halide bonding dominates the structures of heteroleptic halide pyridine-amide Cu II complexes were reported before [3,5,[25][26][27]38,40]. Using the same reaction protocol but varying the Cu:ligand ratio, 10 out of these 18 compounds could be reliably reproduced in good to excellent yields and high phase purity as confirmed through elemental analyses and powder XRD (Scheme 2). In turn, this means that the compounds 2, 4, 11, and 14 remained unreproducible.

For some of the compounds such as [Cu
For other compounds, the optimum ratio lies more to the Cu side with the most remarkable example being [Cu(Ina)4(H2O)2](BF4)2 (1) for which a 2:1 = Cu:ligand ratio was best to observe phase pure material, while a 1:4 ratio prevails in the compound. The most important parameter for the assessment of the synthesis was the phase purity. The second important parameter was the yield. However, it is important to note, that yields were either calculated based on Cu or based on the ligand. For example, for compound (1) a 2:1 ratio in the starting material meant a high yield relative to the ligand (88%) but, of course, a very low yield relative to the starting Cu II precursor (22%).
IR spectroscopy allowed revealing some structural features of the compounds (data in the Experimental Section). The presence of BF4 − , ClO4 − , and NO3 − in the compounds as ligands or as counter anions is easily detectable through their characteristic vibrational modes. On the other hand, the data did not unequivocally allow determining whether these anions are ligands or counter ions. For other compounds, the optimum ratio lies more to the Cu side with the most remarkable example being [Cu(Ina) 4 (H 2 O) 2 ](BF 4 ) 2 (1) for which a 2:1 = Cu:ligand ratio was best to observe phase pure material, while a 1:4 ratio prevails in the compound. The most important parameter for the assessment of the synthesis was the phase purity. The second important parameter was the yield. However, it is important to note, that yields were either calculated based on Cu or based on the ligand. For example, for compound (1) a 2:1 ratio in the starting material meant a high yield relative to the ligand (88%) but, of course, a very low yield relative to the starting Cu II precursor (22%).
IR spectroscopy allowed revealing some structural features of the compounds (data in the Experimental Section). The presence of BF 4 − , ClO 4 − , and NO 3 − in the compounds as ligands or as counter anions is easily detectable through their characteristic vibrational modes. On the other hand, the data did not unequivocally allow determining whether these anions are ligands or counter ions. Quite generally, the coordination to Cu leads to slight blue-shifts of characteristic ligand vibrations. However, there are exceptions like the compounds containing pyrazine 2-amide (Pya). The ν(C=O) resonances for the compounds were found markedly at lower energy compared with those of the uncoordinated ligand. Interestingly, the δ(NH 2 ) resonances of the amide ligands are usually red-shifted upon coordination and suffer from a marked loss of intensity. However, in none of our structures did the NH 2amide function act as coordinating (see next paragraph). Thus, IR spectroscopy does not allow the unequivocal assignment of structural details.

Crystal Structures from Single Crystal XRD
The compounds listed in Table 1 could be obtained as single crystals suitable for single-crystal XRD directly from the reaction mixtures. Amongst the structures we found the 1D coordination polymers 2 ( Figure  The ν(C=O) resonances for the compounds were found markedly at lower energy compared with those of the uncoordinated ligand. Interestingly, the δ(NH2) resonances of the amide ligands are usually red-shifted upon coordination and suffer from a marked loss of intensity. However, in none of our structures did the NH2amide function act as coordinating (see next paragraph). Thus, IR spectroscopy does not allow the unequivocal assignment of structural details.

Crystal Structures from Single Crystal XRD
The compounds listed in Table 1 could be obtained as single crystals suitable for single-crystal XRD directly from the reaction mixtures. Amongst the structures we found the 1D coordination polymers 2 (Figure 1    usually red-shifted upon coordination and suffer from a marked loss of intensity. However, in none of our structures did the NH2amide function act as coordinating (see next paragraph). Thus, IR spectroscopy does not allow the unequivocal assignment of structural details.

Crystal Structures from Single Crystal XRD
The compounds listed in Table 1 could be obtained as single crystals suitable for single-crystal XRD directly from the reaction mixtures. Amongst the structures we found the 1D coordination polymers 2 (Figure 1 (Figure 4 and Figure S11) with two HIna + cations occupying the axial positions with the C1=C2 bond of the pyridine ring (Figure 4, left). Although, the Cu· · · C=C centroid distance is rather long (3.360(1) Å) we consider this as a bonding contribution.
In the compounds 1, 3, 4, and 7 containing the Ina ligand and 11 which contains the 4-NH 3 protonated 4-HAba + ligand isolated Cu II complexes were found. In their structures weak intermolecular forces as hydrogen bridges and π-π stacking are observed. Importantly, such forces were found in all compounds and we cannot neglect their role on the geometry around Cu II which is decisive for the physical properties. Nevertheless, these non-covalent forces will not be further discussed, as we wanted to focus on the spectral consequences of the geometry around the Cu centre and not its origin.
The predominant coordination unit around Cu II in most of the compounds reported herein is of the frequently observed tetragonally distorted octahedral type (OE in Table 2) [33,37,[41][42][43][44][45][46][47][48]. The short equatorial positions are dominated through the N pyridine, pyrazine and aminophenyl functions. O amide occurs in this plane only in chelates with these N functions, NH 2amide -Cu binding was not observed. The Cu II -ligand bonds in the equatorial plane lie in the range of 1.93 to 2.08 Å and are comparable with previously reported complexes of these ligands [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][38][39][40][41][42][43][44][45][46]. Remarkably, the shortest Cu-ligand bonds were of the Cu-O amide type and were found for the chelating Pia, Pya, and 2-Aba ligands, but also for terminating binding of the 4-Aba ligands including the 4-HAba + cation.    For the labelling of the structures as OE in Table 2, two axial ligands must be present in a distance elongated to about 10-20% compared to the same ligand in an equatorial position [42]. Further observed cases were square pyramidal structures (Spy in Table 2), two structures containing one long axial and one even longer axial Cu-ligand bond (Spy+1) and the peculiar case of two very long distances to Cu II as in (HIna) 2  the sixth ligand is not only elongated but also displaced from the ideal position showing an "axial" angle of about 170 • . Nevertheless, we assign this to Spy+1. In 14 ( Figure S30) the coordination around Cu II showed a severely and multiply distorted octahedron (OD).
Non-chelated O amide binding to Cu II was found in the axial (weak) positions only in one compound (2) and no NH 2amide coordination, in line with the observation that amide functions in amino acids do not represent an important class of ligands in metalloproteins [34][35][36] and the poor non-biologic coordination chemistry of amides and Cu [33,35,37]. Indeed, searching the CCDC database, gave only the Cu II complex [Cu(L) 2 (OH) 2 ] containing two chelating pyrazine-2,3-dicarboxamide ligands with Cu-NH 2amide bonds [49]. Further frequent ligands in the axial positions of our structures were weak ligands as NO 3 − , EtOH, H 2 O, BF 4 − , and the peculiar SiF 6 2− (Figure 4). Nevertheless, the non-chelating

X-Band EPR Spectroscopy and Magnetic Measurements
X-Band EPR spectra of the microcrystalline materials were recorded at 298 and 110 K, Figures 5  and 6 show representative examples, Table 3 lists essential parameters.
For the labelling of the structures as OE in Table 2, two axial ligands must be present in a distance elongated to about 10-20% compared to the same ligand in an equatorial position [42]. Further observed cases were square pyramidal structures (Spy in Table 2), two structures containing one long axial and one even longer axial Cu-ligand bond (Spy+1) and the peculiar case of two very long distances to Cu II as in (HIna)2[CuCl4] (6) (Figure 4, left) called square planar +2 (SQ+2). In compound 10 ( Figure S19) the sixth ligand is not only elongated but also displaced from the ideal position showing an "axial" angle of about 170°. Nevertheless, we assign this to Spy+1. In 14 ( Figure S30) the coordination around Cu II showed a severely and multiply distorted octahedron (OD).
Non-chelated Oamide binding to Cu II was found in the axial (weak) positions only in one compound (2) and no NH2amide coordination, in line with the observation that amide functions in amino acids do not represent an important class of ligands in metalloproteins [34][35][36] and the poor non-biologic coordination chemistry of amides and Cu [33,35,37]. Indeed, searching the CCDC database, gave only the Cu II complex [Cu(L)2(OH)2] containing two chelating pyrazine-2,3dicarboxamide ligands with Cu-NH2amide bonds [49]. Further frequent ligands in the axial positions of our structures were weak ligands as NO3 − , EtOH, H2O, BF4 − , and the peculiar SiF6 2− (Figure 4). Nevertheless, the non-chelating N4pyrazine function of the Pyc − ligand (in 12) was found in the axial position. Importantly, the axial non-chelating Oamide (in 2) and N4pyrazine binding (in 12) both represent structures with µ-O,N ditopic bridging. The axial position is occupied by the thio-bisacetamide (Tba) S atoms in compound 18 in line with the preferences of Cu II to N over S coordination [33,34,50].

X-Band EPR Spectroscopy and Magnetic Measurements
X-Band EPR spectra of the microcrystalline materials were recorded at 298 and 110 K, Figures 5  and 6 show representative examples, Table 3 lists essential parameters.       EPR spectra of axial, rhombic and isotropic geometry were observed and, having full structural information from XRD, will be correlated to the local environment of the Cu II centres in the following.
An isotropic broad spectrum with g values around 2.15 was observed for [Cu(Pyc)(Tfa)](12) containing a square pyramidally coordinated Cu II (group III). An isotropic spectrum was also found for the structurally ill-defined [Cu(Ina) 2 Br 2 ] (5). Our findings for 5 are in line with the reported spectrum and g values for this compound by Atac et al. [22], while for the [Cu(Ina) 2 Cl 2 ] derivative this group reports a rhombic spectrum. From our EPR results we conclude a square pyramidal coordination for Cu II in [Cu(Ina) 2 Br 2 ] (5).
A rather uncommon inverse axial EPR spectrum was observed for [Cu 2 (Aba) 2

(H 2 O) 3 (NO 3 ) 3 ](NO 3 ) (14)
. This type of symmetry is frequently observed for either axially compressed octahedral structures, {dz 2 } 1 ground states, or both, in contrast to the predominant {dx 2 -y 2 } 1 and axially elongated octahedral coordination [38,48,54,55]. However, this structure represents several marked distortions from octahedral geometry, but not a compression. So, we can conclude a {dz 2 } 1 electronic ground state for the two Cu II centres in this compound.

sorption Spectroscopy in the Solid and in Solution
ll microcrystalline materials show colours corresponding to absorptions in the visible reg absorption spectroscopy on selected samples (Table 5) reveals low-wavelengths absorpti g from 640 to 780 nm (15,600 to 12,820 cm −1 ) which were assigned to the typical Cu II d 9 syst rison of the three Pya-containing species reveals that the highest absorption energy ed for [Cu(Pya)2](BF4)2 (9) with a tetrahedrally elongated (OE) structure, followed a)2(H2O)(NO3)](NO3) (10) having an SPy+1 configuration with the sixth ligand marke ted, while [Cu(Pya)(NO3)2] (11) exhibits a maximum red-shifted by 2810 cm −1 in line with pyramidal (SPy) coordination. The long-wavelength absorption observed c)(Tfa)](12) is rather high in energy in view of the only five coordinating atoms. Thi ly due to the Tfaligand with a very short Cu-O distance indicative for its binding streng (Ina)2Br2] we found approximately the same absorption maximum as reported [22] in keep e assumption that we have obtained the same structure.

Absorption Spectroscopy in the Solid and in Solution
All microcrystalline materials show colours corresponding to absorptions in the visible region. UV-vis absorption spectroscopy on selected samples (Table 5) reveals low-wavelengths absorptions ranging from 640 to 780 nm (15,600 to 12,820 cm −1 ) which were assigned to the typical Cu II d 9 system. Comparison of the three Pya-containing species reveals that the highest absorption energy is recorded for [Cu(Pya) 2 ](BF 4 ) 2 (9) with a tetrahedrally elongated (OE) structure, followed by [Cu(Pya) 2 (H 2 O)(NO 3 )](NO 3 ) (10) having an SPy+1 configuration with the sixth ligand markedly elongated, while [Cu(Pya)(NO 3 ) 2 ] (11) exhibits a maximum red-shifted by 2810 cm −1 in line with its square pyramidal (SPy) coordination. The long-wavelength absorption observed for [Cu(Pyc)(Tfa)] (12) is rather high in energy in view of the only five coordinating atoms. This is probably due to the Tfaligand with a very short Cu-O distance indicative for its binding strength. For [Cu(Ina) 2 Br 2 ] we found approximately the same absorption maximum as reported [22] in keeping with the assumption that we have obtained the same structure.
A view of a collection of similar structures (  [24], elongated octahedral coordination can be reasonably assumed from the UV-vis data, while the structure of [Cu(clof) 2 (Ina) 2 ] probably represents a square pyramid.

Methods and Instrumentation
1 H and 13 C NMR spectra were recorded in DMSO-d 6 using a Bruker Avance II 300 spectrometer (Bruker, Rheinhausen, Germany). Elemental analyses were carried out using a HEKAtech CHNS EuroEA 3000 Analyzer (Hekatech, Wegberg, Germany). IR spectra were recorded using KBr or polyethylene pellets using an IFS/66v/S or an Alpha-T spectrometers (Bruker, Rheinhausen, Germany). UV-vis absorption spectra were measured on transparent KBr pellets using a Shimadzu UV-3600 photo spectrometer (Shimadzu Europe, Duisburg, Germany). EPR spectra were recorded in the X-band on a Bruker System ELEXSYS 500E equipped with a Bruker Variable Temperature Unit ER 4131VT (500 to 100 K) (Bruker, Rheinhausen, Germany). The g values were calibrated using a dpph sample. The magnetic measurements were carried out on finely ground samples using a MPMS XL7 (Quantum Design, Darmstadt, Germany) instrument measuring from 2 to 300 K at a magnetic field of 1 T.

Powder X-ray Diffraction (PXRD)
Data collection was carried out with a Huber G670 diffractometer (Huber, Rimsting, Germany) equipped with a Ge(111) monochromator using Cu-Kα1 radiation with λ = 1.5405 Å and an image plate detector. The samples were measured as flat samples between two almost X-ray transparent foils. The foil gives rise to two broad reflections at 2θ ≈ 21.5 • and 2θ ≈ 23.7 • . PXRD data were visualised with the WinXPOW software package (STOE & Cie., 2012, Darmstadt, Germany) [62], which was also used to calculate line diagrams based on single crystal data. Gnuplot4.6 was used for the visualisation of PXRD patterns [63].

General
Picolinamide and nicotinamide were synthesised from their (commercially available) carboxylic acids (details in the Supplementary Materials), all other chemicals were used as supplied. Water-free reactions were carried out under inert gas conditions and performed using Schlenk techniques. Solvents were dried using an MBRAUN MB SPS-800 (MBRAUN, Garching, Germany) solvent purification system.

Synthesis of the Cu II Compounds-General Method
The following compounds were synthesised through dissolving suitable Cu II salts in EtOH, heating these solutions to 70 • C and then slowly adding the ligands to the mixture. Upon standing and slow evaporation of the solvent at ambient temperatures in the fume hood, the materials were obtained in yields from 39 to 75% referring to the Cu II starting material and from 30 to 90% referring to the ligand.
[Cu(Ina) 4   (2) with KBr in a mortar. The compound was previously reported [39] but no details as to the Cu:ligand ratio were provided.

Conclusions
New Cu II complexes and coordination polymers of isonicotineamide (Ina) and picolinamide (Pia), pyrazine 2-amide (Pya), 2-and 4-amino benzamides (2-Aba and 4-Aba) ligands were synthesised from various Cu II sources. Under the criterion of crystallinity and phase purity we were able to reliably reproduce many of the materials in reasonable yields. Crystal and molecular structures from single-crystal XRD were obtained for all new compounds; phase purity was checked using powder XRD. For the optimisation of the reaction protocols, the Cu:ligand stoichiometry of the starting materials was varied and we observed marked deviations of the Cu:ligand ratio in products compared with the starting materials. For three compounds containing the pyridine amides Ina and Pia, high Cu loadings of 2:1 were necessary to obtain phase pure compounds with Cu:ligand ratios of 1:4 and 1:2. In contrast to this, for the amino benzamide 4-Aba the optimum ratio of starting materials was 1:3 or 1:2 to obtain compounds with a Cu:ligand ratio of 1:2. In the structures, we exclusively observed O amide and not NH 2amide binding to Cu II , in most of the cases supported by chelating of the second N binding function (pyridine, pyrazine, or aminophenyl) on the ligands. The ditopic ligands Ina, Pya, and 4-Aba frequently bridge µ-O,N between Cu II centres forming 1D or 2D coordination polymers. Again, no NH 2amide binding occurred. However, the same ligands were also found in terminal non-bridging modes. Nitrate, NO 3 − , is often competing with amide ligand binding and might be one important reason for the saturation of Cu II preventing the µ-O,N bridging and formation of polymers. The coordination surrounding Cu II in these structures is dominated by the ubiquitous axial elongated octahedral geometry (OE). The second important coordination polyhedron is the square pyramid (SPy). The occurrence of these two polyhedra cannot be correlated with the polymeric or non-polymeric character of the compounds. The strong pyridine, pyrazine, or aminophenyl-N functions dominate the equatorial binding plane. O amide occurs in this plane only in chelates with these N functions. Non-chelated O amide binding to Cu II was found in the axial (weak) position as expected, alongside with other weak ligands such as NO 3 − , EtOH, H 2 O, BF 4 − , and the peculiar SiF 6 2− . X-band EPR spectra of powder samples revealed various spectral symmetry patterns ranging from axial over rhombic to inverse axial. Although the EPR spectra cannot be unequivocally correlated to the observed geometry of Cu II in the solid state structures, the EPR patterns can help to support assumed structures as shown for the compound [Cu(Ina) 2 Br 2 ] (Ina = isonicotine amide). As UV-vis absorption spectroscopy and magnetic measurements in the solid can also be reasonably correlated with the surrounding of Cu II , we suggest the combination of EPR, UV-vis spectroscopy, and magnetic measurements to elucidate or support possible structures of Cu II compounds with such ligands if no unequivocal structural information is available.
As we can reliably reproduce some of the presented materials here, we will study the biological properties, for example, the antiproliferative activity of selected compounds, in the near future. Funding: General funding is gratefully acknowledged to the University of Cologne. A.K. acknowledges the German Academic Exchange Service (DAAD)-KD_0001052598-2 for a short-time guest lectureship and the Shiraz University, Iran, for support.