Solid State Structural Variations in Copper(II) Complexes of Open

Article pubs.acs.org/crystal

Solid State Structural Variations in Copper(II) Complexes of OpenChain and Macrocyclic Malonamide-Derived Ligands Sergey P. Gavrish,† Yaroslaw D. Lampeka,*,† Philip Lightfoot,‡ Vladimir B. Arion,§ Bernhard K. Keppler,§ and Krzysztof Woźniak∥ †

L.V.Pisarzhevskii Institute of Physical Chemistry of the National Academy of Sciences of Ukraine, Prospekt Nauki 31, Kyiv 03028, Ukraine ‡ School of Chemistry, University of St Andrews, St Andrews KY16 9ST, U.K. § Institute of Inorganic Chemistry of University of Vienna, Währinger Strasse 42, 1090 Wien, Austria ∥ Chemistry Department, Warsaw University, ul. Pasteura 1, 02093 Warszawa, Poland S Supporting Information *

ABSTRACT: An analysis of the molecular structure of the copper(II) complexes with open-chain and macrocyclic malonamide-derived tetradentate ligands based on single crystal X-ray diffraction study of four copper(II) complexes [CuL 1 (H 2 O)]·4H 2 O, [CuL 2 (H 2 O)], [CuL 3 (H 2 O)], and [CuL4(H2O)] (H2L1 = 1,4,8,11-tetraazaundecane-5,7-dione, H2L2 = 13methyl-13-nitro-1,4,8,11-tetraazacyclotetradecane-5,7-dione, H2L3 = 1,4,8,11tetraazacyclotetradecane-5,7-dione, and H2L4 = 1,4,8,11-tetraazacyclotridecane-5,7-dione) as well as on published data regarding related compounds revealed that the violations of planarity of the metalamide fragments are due almost exclusively to the deviation of the copper(II) ion from the amide plane. Both the deviation of the copper(II) ion from the amide plane and the angle between amide planes in the 6-membered malonamide ring are strongly affected by substituents with minimal values observed in the complexes of unsubstituted ligands. The deviation of the copper(II) ion from the basal plane of donor atoms was shown to relate to the sum of bite angles around the copper(II) ion and roughly correlates to Cu−Lax distances when apical ligands are present. The crystals of the macrocyclic complexes CuL2 to CuL4 are built up from similar corrugated layers in which metal complex molecules are linked in a “head-to-tail” manner via NH···OC hydrogen bonds. In contrast, [CuL1(H2O)]·4H2O has a lamellar crystal structure in which the layers built up of [CuL1(H2O)] units alternate with sheets formed by water molecules.

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species called “molecular machines” with the metal ions movable between two coordination sites.12 On the other hand, the insertion of the substituents into the “tetraamine” part of dioxotetraazamacrocycles via traditional synthetic methods meets obvious obstacles and, to the best of our knowledge, no such compounds have been described. At the same time, Mannich-type metal-templated reactions of formaldehyde with nucleophiles have been extensively employed for the synthesis of substituted oxo-free macrocyclic polyamines.16,17 Previously we have shown that these reactions are applicable also for the synthesis of nickel(II) and copper(II) complexes of macrocyclic dioxotetraamines.18,19 In particular, the reaction of the complex of the open-chain ligand CuL1 with formaldehyde and nitroethane led to macrocyclic compound CuL2.18 A number of the copper(II) complexes of the C-substituted open-chain (CuL5,20 CuL6,7a CuL7,7b CuL8 (ref 10a)) and of the N-substituted macrocyclic 13-membered14 and 14-mem-

INTRODUCTION

The coordination chemistry of open-chain and macrocyclic dioxotetraamines has been intensively studied during the past decades.1,2 Ligands of this type effectively stabilize high oxidation states of the transition metals, e.g. nickel(III) and copper(III).3,4 Due to the presence of the structural features of both amines and peptides, such species have been used as biomimetic systems, specifically for the study of the superoxide dismutase activity of the copper complexes.5 Among ligands of this type, the malonamide-derived dioxotetraamines are the most widely studied1 because of preparative accessibility via one-pot aminolysis reactions of the malonic esters and wide possibilities of introducing substituents at the methylene group of the malonic esters (C-substitution). These functionalized compounds include species with redox active,6 fluorescent,7,8 lipophilic,9 as well as coordinating10,11 groups. Another method of modification of the ligand backbone offers the alkylation of the amine nitrogen atoms (N-substitution) in open-chain12 or macrocyclic13−15 dioxotetraamines with substituents bearing donor centers. When functional groups of such substituents are able to form chelate rings, this approach leads to interesting © 2012 American Chemical Society

Received: April 23, 2012 Revised: July 19, 2012 Published: August 13, 2012 4388

dx.doi.org/10.1021/cg300554r | Cryst. Growth Des. 2012, 12, 4388−4396

Crystal Growth & Design

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Scheme 1. Structures of the Copper(II) Complexes of Malonamide-Derived Ligands

Table 1. Crystal Data and Structure Refinement for the Copper(II) Complexes of Malonamide-Derived Ligands empirical formula formula weight T (K) crystal system space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z Dcalc (g cm−3) μ (mm−1)] F(000) reflections collected/unique data/restraints/parameters GOF on F2 R1/wR2 [I > 2σ(I)] R1/wR2 (all data)

[CuL1(H2O)]·4H2O

[CuL2(H2O)]

[CuL3(H2O)]

[CuL4(H2O)]

C7H24CuN4O7 339.84 100(2) monoclinic P21/c 9.3425(3) 7.2460(2) 21.9747(8) 101.798(2) 1456.17(8) 4 1.550 1.533 716 35222/2883 2883/18/184 1.082 0.0670/0.1644 0.0677/0.1647

C11H21CuN5O5 366.87 293(1) orthorhombic Pnma 13.828(4) 9.634(3) 10.941(4) 90 1457.5(8) 4 1.672 1.531 764 1325/1202 1202/0/114 0.990 0.0523/0.1480 0.0570/0.1539

C10H20CuN4O3 307.84 293(2) orthorhombic Pnma 10.7428(11) 9.3864(10) 12.5692(13) 90 1267.4(2) 4 1.613 1.731 644 23001/1708 1708/0/88 1.179 0.0549/0.1048 0.1093/0.1442

C9H18CuN4O3 293.81 100(2) monoclinic P21 7.1509(14) 11.773(2) 7.1509(14) 101.66(3) 589.6(2) 2 1.655 1.856 306 2303/2303 2303/4/155 1.069 0.0211/0.0557 0.0212/0.0559

bered15 malonamide-derived dioxotetraamines, as well as of the dicopper(II) complexes of the C-”self”-substituted ligands (Cu2L9,21 Cu2L10,5b Cu2L18 (ref 22)), have been structurally characterized (for the ligand abbreviations, see Scheme 1). Depending on the structure of the ligands, different conformations of their chelate rings as well as degrees of distortion of the copper(II) coordination polyhedrons have been observed. As for the latter, in the majority of cases, the metal ion is displaced out of the plane of equatorial donor atoms toward the apical ligand, though no correlation between such displacement and copper(II)−apical ligand distance has been stated.

Surprisingly, no structural data have been reported to date for the copper(II) complexes of unsubstituted dioxotetraamines H2L1, H2L3, and H2L4the ancestors of the series of the openchain and the 13- and 14-membered macrocyclic ligands. Therefore, the present work is dedicated to the estimation of the molecular structures of the copper(II) complexes CuL1, CuL3, and CuL4, as well as of the product of formaldehyde/ nitroethane cyclization, CuL2. The results obtained and data published in the literature are analyzed in order to estimate the influence of the ligand on the structure of the copper(II) complexes in the solid state. The peculiarities of packing and hydrogen bond networks in the CuL1 to CuL4 are also discussed. 4389



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Figure 1. Perspective views of the complexes [CuL1(H2O)]·4H2O (a), [CuL2(H2O)] (b), [CuL3(H2O)] (c), and [CuL4(H2O)] (d). Thermal ellipsoids are drawn at the 30% probability level; hydrogen atoms at carbon and lattice water molecules in part a are not shown.

Table 2. Selected Interatomic Distances (Å) and Angles (deg) for the Copper(II) Complexes of Malonamide-Derived Ligands

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Cu−Namide Cu−Namine Cu−O(H2O) (C−O)amide (C−N)amide Namide−Cu−Namide Namide−Cu−Namine Namine−Cu−Namine Namide−C−C−Namine

[CuL1(H2O)]·4H2O

[CuL2(H2O)]

[CuL3(H2O)]

[CuL4(H2O)]

1.944(5); 1.950(5) 2.010(5); 2.011(5) 2.466(5) 1.273(7); 1.274(7) 1.300(7); 1.302(7) 94.6(2) 83.9(2); 84.0(2) 96.7(2) 41.4(7); 42.4(7)

1.932(3) 2.042(3) 2.560(4) 1.254(4) 1.325(4) 95.5(2) 84.8(2) 94.6(2) 45.5(4)

1.938(3) 2.026(3) 2.496(5) 1.260(4) 1.310(5) 95.3(2) 84.7(2) 94.3(2) 45.1(5)

1.922(3); 1.925(3) 2.022(3); 2.023(3) 2.339(2) 1.261(5); 1.267(5) 1.304(5); 1.307(5) 95.5(1) 85.6(1); 86.3(1) 86.1(1) 47.8(4); 48.8(4)

eters [λ(Mo Kα) = 0.71073 Å, graphite monochromator). The structures were solved by direct methods25 and refined on F2 by fullmatrix least-squares techniques using the SHELXTL software package.26 All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were placed in calculated positions, or their positions were determined from difference Fourier maps and refined isotropically. One of the two hydrogen atoms in two crystalline water molecules (O(2) and O(3)) in [CuL1(H2O)]·4H2O is disordered over two positions. Two remaining crystalline water molecules in this compound are disordered over two positions with occupancy factor 0.5, and their protons were not localized. A summary of the crystallographic data and structure determination parameters is provided in Table 1.

EXPERIMENTAL SECTION 1 23

3

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Syntheses. The ligands H2L , H2L , and H2L (ref 24) and the copper(II) complexes CuL1,23 CuL2,18 and CuL3 (ref 4) were prepared according to the literature procedures. The complex CuL4·2.5H2O was isolated as follows. Cu(OH)2 (60 mg, 0.61 mmol) was added to a solution of H2L4 (100 mg, 0.47 mmol) in methanol (15 mL) and water (3 mL), and the suspension was stirred at room temperature for 15 h. Unreacted copper hydroxide was filtered off and the filtrate evaporated to dryness by rotary evaporation. The residue was dissolved in methanol (2 mL), and acetonitrile (12 mL) was added. The solution was filtered and concentrated on a rotary evaporator to a volume of ca. 5 mL. The resulting blue-violet solid was filtered off, washed with acetonitrile and acetone, and dried on air. Yield 78 mg (52% based on ligand). Anal. Calcd for C9H21N4O4.5Cu: C, 33.69; H, 6.60; N, 17.46. Found: C, 33.18; H, 6.40; N, 17.54. Single crystals of the complexes suitable for X-ray analysis were grown by diffusion of acetonitrile into aqueous solutions of complexes (CuL1 and CuL4) or by diffusion of acetone into aqueous solution of CuL2 or into solution of CuL3 in ethylene glycol containing minimal amount of water. X-ray Data Collection and Structure Determination. X-ray diffraction measurements were performed on Bruker X8 APEXII CCD ([CuL1(H2O)]·4H2O, [CuL4(H2O)]), Rigaku AFC7S ([CuL2(H2O)]) and Kuma KM4CCD ([CuL3(H2O)]) diffractom-

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RESULTS AND DISCUSSION Molecular Structure of the Complexes. The copper(II) ion in all compounds studied has a similar (4 + 1) squarepyramidal environment, with the basal plane formed by two deprotonated amide atoms and two amine donor atoms of the ligand and the water molecule occupying the apical position. Perspective views of the [CuL(H2O)] coordination unit with the atom numbering scheme employed are shown in Figure 1. 4390



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Despite similar lengths of the Cu−N bonds, the conformations of the malonamide chelate ring in the complexes under consideration display pronounced differences. The analysis shows that in all copper(II) complexes the coplanarity of the five atoms of the amide fragment CNC(O) C is retained to a good degree of accuracy (the rms deviations of these atoms from their mean plane do not exceed 0.04 Å). Such planes (further referred to as amide planes) for two amide groups form an angle γ (Figure 2); that is, the malonamide chelate rings on the whole can be considered as being folded.

Selected geometric parameters of the complexes are collected in Table 2. The complexes of the 14-membered macrocyclic ligands CuL2 and CuL3 possess a mirror plane with coplanar N4 donor atoms. The complex CuL1 exhibits a close to mirror symmetry with a very small (0.003 Å) deviation of the nitrogen atoms from the mean N4-plane. The copper(II) ions are displaced out of this plane toward the apically coordinated water molecule by 0.123 (CuL1), 0.072 (CuL2), and 0.139 Å (CuL3). These features resemble those for the majority of the five-coordinated copper(II) complexes of the open-chain and 14-membered macrocyclic ligands described in the literature, which are characterized by rather small distortions of the donor atom plane (rms deviation < 0.08 Å). Apical water ligands, when present, are located at similar distances (2.460 and 2.564 Å for Cu2L9 and Cu2L10, respectively; cf. with the data quoted in Table 2), while the distances to strongly coordinating pyridine (CuL8) or quinoline (CuL12) pendants are much shorter (2.350 and 2.263 Å, respectively). In the only six-coordinated complex CuL13, two quinoline donors are located at both sides of the macrocycle plane with relatively long Cu−N distances (2.686 and 2.800 Å), with the copper(II) ion lying almost exactly in the plane of equatorial donors. At the same time, in a number of complexes (CuL5, CuL6, CuL7, CuL11) apical ligands are absent, and these compounds are four-coordinated. As well as in other complexes of the 13-membered macrocyclic ligands, the coordinated amine nitrogen atoms in CuL4 possess opposite chirality (R,S) and its structure is characterized by a Flack parameter of 0.08(2). The coordination polyhedra in this case are less symmetric and reveal much larger deviations of the nitrogen atoms from their mean plane (rms values 0.117−0.161 Å; 0.119 Å for CuL4). The copper−apical ligand distances in the complexes of the 13membered macrocycles are always shorter (2.204−2.340 Å), and the displacement of the copper(II) ion from the N4-plane toward the apical ligand is much larger (0.353−0.405 Å; 0.353 Å for CuL4). As one can see, the structure of the equatorial ligand in the complexes under consideration exerts a rather small influence on the Cu−Namine bond lengths (Table 2), and this is supported by the analysis of the literature data (cf. the ranges of Cu−Namine distances 2.034−2.084, 2.026−2.105, and 1.995− 2.046 Å for complexes of 14-membered, 13-membered, and open-chain ligands, respectively). Longer Cu−Namine bonds for the nitro-derivative CuL2 as compared to CuL3 can probably be explained by a strong electron-withdrawing effect of the substituent (the presence of the nitro group increases the CuIII/IIL redox potential by ca. 140 mV).18 Replacement of the hydrogen atom of the amide group by the metal ion leads to the enhanced electron delocalization within the amide fragment, which is reflected in lengthening of (C−O)amide and shortening of (C−N)amide distances as compared to uncoordinated ligands (cf. the data quoted in Table 2 with 1.230 and 1.335, and 1.224 and 1.331 Å for metalfree H2L3 (ref 27) and H2L4,28 respectively). Coordination bonds between the metal ion and negatively charged nitrogen atoms of the deprotonated amide groups (Cu−Namide) are considerably shorter than Cu−Namine ones and slightly decrease in the following series: CuL1 > CuL2, CuL3 > CuL4 (Table 2). Such a tendency is in agreement with the general trend of shortening of Cu−N distances in passage from open-chain ligand via 14-membered to 13-membered macrocycles (see Table S1 in the Supporting Information).

Figure 2. Definition of angular characteristics of the malonamide chelate ring.

The values of the angle γ (see Table S1 in the Supporting Information) are among the smallest for complexes of unsubstituted ligands studied in the present work, i.e., 1.4° (CuL1), 17.4° (CuL2), 18.2° (CuL3), and 25.4° (CuL4). Particularly, in CuL1 the malonamide chelate ring in whole is characterized by an extremely flat geometry with the rms deviation of the ring atoms from their mean plane of only 0.03 Å and an abnormally large (124.9°), for a sp3-hybridized atom, value of the bond angle for the apical carbon atom (angle α, Figure 2), thus resembling the nickel(II) and palladium(II) analogues.29 It is noteworthy that the insertion of virtually any substituent at the apical methylene carbon leads to a folding of the ring by more than 40°, as compared to CuL1, which is usually accompanied by a decrease of α. Therewith, for the complexes CuL2 to CuL4 and CuL11, the values of α remain practically as large as those for CuL1, despite considerable nonplanarity of the malonamide ring. To ensure strict planarity of the metal-containing amide fragments CN(Cu)C(O)C, the copper(II) ion should be located on the intersection of two amide planes (see Figure 2), and this can be realized only for the “boat” (but not “chair”!) conformation of the 6-membered ring. Indeed, “boat” conformations are often encountered, in particular in all complexes of the 13-membered macrocycles. However, chairlike conformations can also be observed for complexes of the open-chain and 14-membered macrocyclic ligands, e.g. for CuL1 and CuL2. The deviation of the amide (peptide) groups from planarity is an important issue addressed in numerous works on organic amide/polypeptide chemistry,30 but it attracted relatively little attention in the realm of coordination chemistry.31 Since the original work of Winkler and Dunitz,32 a set of three angles (χC, χN, τ; see Figure S1 and Table S1 in the Supporting Information) is used for characterization of this phenomenon. Since the coplanarity of the CNC(O)C fragment in the copper(II) complexes is retained to a good degree of accuracy, we suggest to introduce for this purpose a single parameter, namely, the angle φ formed by the Cu−Namide vector to the amide plane (Figure 2), which can be expressed as a linear 4391



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combination of Dunitz parameters: φ = −0.12χC + 0.40χN + 0.82τ (see Figure S2 in the Supporting Information). In general, the largest violations of the amide planarity are observed for the complexes of open-chain ligands with the maximal φ reaching ca. 30° (CuL7). The complexes of the 14and 13-membered macrocycles on the whole are characterized by lower φ angles, and in each series this parameter is among the smallest in complexes of unsubstituted ligands CuL1, CuL3, and CuL4. Therewith, the trend of lengthening of the Cu− Namide bonds with the increasing φ is observed, thus indicating weakening of the Cu(II)−Namide interaction (see Figure S3 in the Supporting Information). Two factors should be mentioned when possible reasons of large distortions of the amide planarity are considered. First, the ideal “boat” conformation of the malonamide ring is not optimal for π-type copper(II)−amide nitrogen interactions (see Figure S4 in the Supporting Information), and this is confirmed by the dependence of Cu−Namide bond lengths on the parameter τMN characterizing π-orbital misalignment (Figure S5 in the Supporting Information). Second, the diamine moiety of the ligand can not adopt the required conformation without considerable strain, and this is reflected in the conformations of the lateral 5-membered chelate rings directly “fused” to the malonamide cycle. Both lateral 5-membered chelate rings in copper(II) complexes adopt either gauche (CuL2 and CuL3) or envelope (CuL1) conformations. At the same time, both gauche and envelope conformations of lateral chelate rings are present simultaneously in CuL4 and in the majority of other complexes of the 13-membered ligands. The Namide−C−C−Namine torsion angles in both gauche and envelope conformations of chelate rings in CuL1 to CuL4 (see Table 2) are smaller than the values of ca. 55° characteristic for the gauche conformation in the copper(II) complexes of the oxo-free analogues 2,3,2-tet33a and cyclam33b (2,3,2-tet = 1,9-diamino-3,7-diazanonane, cyclam = 1,4,8,11-tetraazacyclotetradecane). Without qualms, this fact reflects the strain related to the junction of the malonamide chelate ring with lateral metalocycles. The values of the bite angles Namide−Cu−Namine are similar for all compounds, demonstrating a trend of a small increase in the series of ligands: open-chain (ca. 84°) < 14-membered (ca. 85°) < 13membered (ca. 86° for both lateral and remote chelate rings). Additional 6-membered chelate rings in the complexes of the 14-membered macrocycles adopt a chair conformation with bite angles of ca. 94°, which are slightly smaller as compared to the case of CuL1. This means, in particular, that the transformation of the open-chain ligand into the 14-membered macrocycle brings about only a slight stress in the ligand molecule. Interestingly, despite differences in conformations and in the nature of donor atoms, the differences in the values of N−Cu−N bite angles in 6-membered trimethylenediamine and malonamide chelate rings are surprisingly small (Table 2). Some of the above-mentioned structural features of coordination polyhedra of the copper(II) ion can be rationalized on the basis of simple geometrical considerations concerning mainly the effect of bite angles, since the dependence of Cu−N bonds on the structure of an equatorial ligand appears to be not very significant. It can be shown (see Supplement 2 in the Supporting Information) that a lot of distorted structures of the ML4 polyhedron are possible for a given set of bite angles, including a symmetric one. Symmetric structures are observed in the complexes of the open-chain and 14-membered macrocyclic

ligands but are not realized in the complexes of 13-membered macrocycles because the retention of mirror symmetry in this case would require an energetically unfavorable eclipsed conformation of the central 5-membered chelate ring. On the other hand, it is evident that the deviation of the metal ion from the plane of donor atoms (δ) should be related to bite angles. According to our analysis (see Supplement 3 in the Supporting Information), the relationship between these parameters can be expressed by a simple equation, strict for symmetric polyhedra: δ = κ 360 − Σ

(1)

where κ = 0.066R, 1/R = (1/Ramide + 1/Ramine)/2, Ramide and Ramine are corresponding Cu−N distances (Å), and Σ is the sum of angles (deg) around the metal ion. As can be seen from Figure 3, the agreement between experimental and calculated

Figure 3. Dependence of the deviation (δ) of the copper(II) ion from the mean plane of N4 donor atoms on the sum of the bite angles (circles, complexes of the open-chain ligands; squares, complexes of the 14-membered macrocycles; triangles, complexes of the 13membered macrocycles). The data for CuL6 and CuL13 were omitted because for these complexes Σ > 360°. The curve conforms to eq 1 with κ equal to 0.131 Å, which corresponds to average (all compounds) Cu−Namide and Cu−Namine distances of 1.94 Å and of 2.04 Å, respectively.

data is good for complexes of the open-chain and 14-membered macrocyclic ligands, while deviation of the points corresponding to the complexes of 13-membered macrocycles is obviously related to violations of symmetry. Coordination of the apical ligand is usually considered as an important factor affecting the degree of pyramidality of tetragonal chromophores. Indeed, in all complexes under consideration, the copper(II) ion is displaced from the N4plane toward the apical ligand (if present) and a tendency of the reduction of this displacement with a lengthening of the Cu-axial donor distance is observed (Figure 4). However, a peculiarity of the copper(II) complexes of a given type is that Cu−Lap distances do not correlate to averaged Cu−N distances in the equatorial plane (see Figure S10 in the Supporting Information). Equation 1 can, in our opinion, explain why considerable values of δ are observed even in the absence of the apically coordinated ligand (e.g., 0.146 Å and 0.163 Å in CuL5 and CuL7, respectively). One can note that these δ values correspond to a region where the plot of δ vs (360 − Σ) is 4392



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However, different mutual orientation of hydrogen atoms of secondary amino groups and the apical water molecule results in a marked difference in dimensionality of the hydrogen bond networks. In CuL2 and CuL4 they are located on the same side of the macrocycle plane and H2O molecules provide additional intralayer links between complex molecules. As a result, 2D layers are held together only by van der Waals interactions (Figure 5a and c). In contrast, the H2O molecules in CuL3 are localized on another (relative to NH atoms) side of the macrocycle and they are involved in H-bonding between adjacent layers, thus forming a 3D network of hydrogen bonds (Figure 5b). The complex [CuL1(H2O)]·4H2O crystallizes with four additional water molecules (these are lost very quickly when the crystals are picked from solution; therefore, this compound was described originally as the monohydrate23). Its crystal structure is lamellar (Figure 6a), with metal complex layers built up of [CuL1(H2O)] units (Figure 6b) alternating with the sheets composed solely of water molecules. The contacts between the metal complex and water layers occur via H-bonds between amide oxygen atoms and hydrogen atoms of water molecules H2O(2w) and H2O(3w). Four crystalline water molecules form a honeycomb-like structure (Figure 6c) consisting of fused 6-membered water rings of two types A and B. All distances between neighboring oxygen atoms in the layer are in the range 2.70−2.75 Å, indicating their involvement in hydrogen bond formation (see Table S3 in the Supporting Information). Interestingly, the general topology of the water layer formed in this case is similar to that reported recently for the nickel(II) complex of the oxamide-derived ligand,19 with the main difference consisting in the chair-like vs boat-like conformation of hexagonal water rings in the present and former cases, respectively.

Figure 4. Dependence of the deviation (δ) of the copper(II) ion from the mean plane of donor atoms (N4) on the copper(II) distance to the apical ligand (for symbols see Figure 3). Points corresponding to fourcoordinate compounds are arbitrarily placed at a Cu−Lap distance of 3.0 Å.

extremely steep, and thus, even minor variations in bite angles induced, for example, by packing effects in the solid state can lead to “pushing” the metal ion out of the plane of donor atoms. Crystal Structure of the Complexes. The crystals of the macrocyclic complexes CuL2 to CuL4 are built up of neutral [CuL(H2O)] units and possess a common packing motif in which these units are linked to four neighbors through NH···OC and HOH···OC hydrogen bonds (see Table S3 in the Supporting Information) forming corrugated layers (Figure 5).

Figure 5. Crystal structures of [CuL2(H2O)] (a), [CuL3(H2O)] (b), and [CuL4(H2O)] (c) as viewed down the b crystallographic axis (a, b) and [101] direction (c). 4393



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Figure 6. Crystal structure of [CuL1(H2O)]·4H2O as viewed down the b axis (a) and the structure of the metal complex (b) and water (c) layers as viewed down the c axis (for clarity, the midpoints between two oxygen atom positions with half-occupancy of the disordered water molecules O4w and O5w (o45w) and O6w and O7w (o67w) are shown; A and B are the symmetry equivalents of A and B related by inversion (−x, −y, −z) plus translations).

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violations of the correlation of δ to Cu−Lap distances observed in the absence of apical ligands. The crystal structures of the macrocyclic complexes [CuL(H2O)] (L = L2 − L4) are built up from similar corrugated layers in which complex molecules are linked in a “head-to-tail” manner via NH···OC hydrogen bonds. The interaction between such layers is determined by mutual orientation of the hydrogen atoms of secondary amino groups, and coordinated water molecule−van der Waals interactions only are operative when NH and H2O are on the same side of the macrocycle planes (CuL2, CuL4), while hydrogen bonds with coordinated water molecule are formed when NH and H2O are at opposite sides of the ligand (CuL3). In contrast, [CuL1(H2O)]·4H2O has a lamellar crystal structure in which the layers built up of [CuL1(H2O)] units alternate with the “honeycomb” sheets formed by water molecules.

CONCLUSIONS

The ligands discussed in this paper can be considered as hybrids of malonamide and polyamines; therefore, the formation of coordination bonds with the copper(II) ion requires a compromise between the retention of planarity of the metal-amide fragments and the stereochemical demands of the polyamine moiety of the ligand. The violations of planarity of the copper(II)-amide fragments are due almost exclusively to the deviation of the metal ion from the amide plane and can be described by a single parameter (angle φ). This parameter may be rather large (up to 30°), and the trend, though poorly expressed, exists of lengthening the Cu−Namide bonds with the increase of the amide nonplanarity. The malonamide chelate rings adopt either a “boat” or a “half-chair” conformation with the angle γ between the amide planes in the range 1.4−57.6°. The values of both φ and γ are strongly affected by substituents and are minimal in complexes of unsubstituted ligands. The variations of the Cu−Namide and Cu−Namine bond lengths tend to compensate each other, so that the averaged Cu−N distances in the equatorial plane remain fairly constant and independent of the presence of the apical ligand, though the deviation of the copper(II) ion from the basal plane of donor atoms (δ) roughly correlates to Cu−Lap distances when apical ligands are present. On the other hand, the value of δ is related to the sum of bite angles via a square-root relationship which is characterized by extreme steepness at small argument values. As a result, even minor variations in bite angles may have a profound effect on δ, and this may be responsible for the

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ASSOCIATED CONTENT

S Supporting Information *

Structural characteristics of the malonamide chelate rings in copper(II) complexes, relationships between different parameters characterizing copper(II) chromophores and their possible distortions, derivation of eq 1, and parameters of hydrogen bonds. This material is available free of charge via the Internet at http://pubs.acs.org. CCDC-831909 (for [CuL1(H2O)]·4H2O), -831910 (for [CuL2(H2O)]), -831911 (for [CuL3(H2O)]), and -831912 (for [CuL4(H2O)]) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge 4394



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REFERENCES

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Solid State Structural Variations in Copper(II) Complexes of Open

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