Extended Structures Constructed from Alkoxo-Bridged Binuclear

Extended Structures Constructed from Alkoxo-Bridged Binuclear Complexes as Nodes and Bis(4-pyridyl)ethylene as a Spacer Geanina Marin,† Violeta Tudor,† Victor Ch. Kravtsov,‡ Marc Schmidtmann,§ Yurii A. Simonov,‡ Achim Mu¨ller,§ and Marius Andruh*,†

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 1 279-282

Inorganic Chemistry Laboratory, Faculty of Chemistry, University of Bucharest, Strasse Dumbrava Rosie no. 23, 020464 Bucharest, Romania, Institute of Applied Physics, Academy of Sciences of Moldova, Academy Strasse 5, 2028-Chisinau, R. Moldova, and Fakulta¨ t fu¨ r Chemie der Universita¨ t Bielefeld, Postfach 10 01 31, D-33501 Bielefeld, Germany Received February 27, 2004;

Revised Manuscript Received June 29, 2004

ABSTRACT: Two new polynuclear complexes have been obtained by connecting alkoxo-bridged binuclear copper(II) complexes with bis(4-pyridyl)ethylene (bpe): [Cu2(Hdea)2(bpe)]‚(bpe)‚(ClO4)2 (1) and [Cu2(mea)2(bpe)2](ClO4)2 (2) (Hdea ) mono-deprotonated diethanolamine and mea ) deprotonated monoethanolamine). The structure of 1 consists of infinite chains that have resulted by connecting the bis(alkoxo)-bridged centrosymmetrical [Cu2(dea)2]2+ nodes with bis(4-pyridyl)ethylene rods. The Cu‚‚‚Cu separations within the chain are 2.984 and 13.308 Å. The noncoordinated bpe molecules bind the parallel coordination polymer chains through hydrogen bond interactions, resulting in infinite gridlike sheets. Compound 2 exhibits an interlocked 3-D structure, resulting from the inclined interpenetration of 2-D gridlike sheets. Each sheet is constructed from [Cu2(mea)2] nodes, interconnected by bpe spacers. Every mesh of every sheet contains parts of two others passing through it. The distance between the alkoxobridged copper(II) ions within the nodes is 3.020 Å, while the distances between the copper ions bridged by bpe ligands are 13.381 and 14.051 Å. Introduction The development of crystal engineering has stimulated the search for new building blocks able to generate extended structures with various dimensionalities. Apart from the aesthetic perspective, the interest in this chemistry is justified by the potential utility of these compounds as zeolite-like materials,1 catalysts,2 or magnetic materials.3 A widely used strategy in designing such systems consists of the employment of divergent ligands, which connect metallic centers (the so-called node and spacer approach). The spacers can be either symmetrical or unsymmetrical bridging ligands. The solid-state architecture (dimensionality, topology of the metallic centers) is determined by several factors: (i) metal-to-ligand stoichiometry, (ii) the stereochemical preference (coordination algorithm) of the assembling cations, (iii) the use of ancillary ligands attached to the metal ions or of additional bridging ligands, (iv) the intervention of the noncovalent interactions (hydrogen bonds, π-π stacking interactions), (v) the role of the anions (coordinated, bridging, uncoordinated), and (vi) the presence of the organic guest molecules.4 Taking the case of the 2-D gridlike architectures, these are currently constructed from exo-bidentate ligands and metal ions exhibiting square planar or octahedral stereochemistries, with a ligand-to-metal molar ratio of 2:1. Both linear molecules can act as bridging ligands,5 or only one of them, the other one * Corresponding author. E-mail: [email protected]. † University of Bucharest. ‡ Academy of Sciences of Moldova. § Universita ¨ t Bielefeld.

being uncoordinated. In the last case, the linear chains constructed from metallic centers and bridging ligands are interconnected through the uncoordinated linear molecules, which are most frequently involved in hydrogen bond interactions with the aqua ligands from neighboring chains.6 The most popular exo-bidentate ligands are bis(4-pyridyl)derivatives: 4,4′-bipyridil, bis(4-pyridyl)ethylene, bis(4-pyridyl)ethane, and trans-4,4′azo-pyridine. These systems are covered by some recent excellent reviews.7 Recently, we have shown that homo- and heterobinuclear complexes can be successfully used as nodes in designing extended structures. This represents an extension of the classical node and spacer approach. It also broadens the synthetic concept proposed by Cotton et al., which is based upon binuclear metal-metal bonded cationic species.8 We are currently using the following types of coordination compounds as nodes: (i) binuclear alkoxo-bridged copper(II) complexes,9 (ii) binuclear copper(II) complexes with macrocyclic compartmental ligands,10 and (iii) heterobinuclear 3d-4f complexes with compartmental side-off Schiff-base ligands.11 Following this synthetic approach, we were able to synthesize coordination polymers containing three different paramagnetic ions (3d-3d′-4f),11a as well as the first coordination compound containing three different spin carriers (2p-3d-4f).12 All these compounds have relevance in molecular magnetism. We now report here on two new coordination polymers that have been obtained by connecting alkoxo-bridged binuclear Cu(II) nodes with bis(4-pyridyl)ethylene (bpe): [Cu2(Hdea)2(bpe)]‚(bpe)‚(ClO4)2 (1) and [Cu2(mea)2(bpe)2](ClO4)2 (2) (Hdea ) mono-deprotonated diethanolamine and mea ) deprotonated monoethanolamine).

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Table 1. Crystallographic Data for 1 and 2 chemical formula formula weight crystal system space group unit cell dimensions A (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) Z T (K) cell volume (Å3) density, calculated (gm cm-3) µ (cm-3) λ (Å) goodness of fit final R R indices (all data)

1

2

C32H40Cl2Cu2N6O12 898.68 triclinic P1 h (no. 2)

C14H16ClCuN3O5 405.29 monoclinic P2(1)/c

8.6613(6) 10.5768(8) 11.0798(8) 81.366(10) 80.022(10) 69.272(10) 1 183(2) 930.59(12) 1.596

10.238(2) 11.749(2) 14.548(3) 90 95.35(3) 90 4 293(2) 1742.3(6) 1.545

1.356 0.71073 1.065 0.0552 0.0704

1.435 0.71073 0.826 0.0366 0.0749

Experimental Procedures Syntheses. The two complexes have been prepared as follows: [Cu2(Hdea)2(bpe)](bpe)(ClO4)2 1: an ethanolic solution (15 mL) of Cu(ClO4)2‚6H2O (3.4 mmol) was reacted with H2dea (10.2 mmol) dissolved in 15 mL of ethanol. To the resulted mixture an ethanolic solution (10 mL) of bpe (3.4 mmol) was added. The resulting suspension was filtered, and the filtrate was slowly evaporated. The evaporation of the blue solution led to green single crystals. IR data (KBr, cm-1): 554w, 625s, 833w, 1103vs, 1226w, 1306w, 1428w, 1609s, 2851m, 2929m, 3288s, 3454s. [Cu2(mea)2(bpe)2](ClO4)2 2: an ethanolic solution (15 mL) of Cu(ClO4)2‚6H2O (3.2 mmol) was reacted with Hmea (9.6 mmol) dissolved in 10 mL of ethanol. To the resulted blue solution, an ethanolic solution (5 mL) of bpe (3.2 mmol) has been added. Blue single crystals appeared after several days by slow evaporation of the solution. IR data (KBr, cm-1): 551m, 625m, 829m, 873w, 1080vs, 1107vs, 1422m, 1505w, 1557w, 1610s, 2836m, 2880m, 3131m, 3265m, 3332m, 3443s, 3508s. Caution. Perchlorate salts are potentially explosive and should be handled in small quantities. Crystals 1 and 2 were measured on a Bruker AXS SMART, and respectively, Bruker P4 single-crystal diffractometers, using graphite-monochromated MoKR radiation. The structures were solved by direct methods and refined by full-matrix least-squares techniques based on F2. The non-H atoms were refined with anisotropic displacement parameters. One branch of the Hdea ligand in 1 and the perchlorate anions in both structures were found to be disordered over two positions. Calculations were performed using the SHELX-97 crystallographic software package.13 The crystallographic data and other pertinent information are collected in Table 1.

Results and Discussion The following amino alcohols have been employed to generate binuclear alkoxo-bridegd species: diethanolamine (H2dea) and monoethanolamine (Hmea). In both cases, one OH group from the amino alcohol proligands is deprotonated, and the resulting alkoxo group bridges two copper ions affording the potential nodes for the construction of the coordination polymers. As a spacer, we used the rigid bis(4-pyridyl)ethylene (bpe) molecule. Supramolecular Gridlike Layer. The self-assembly process involving copper(II) ions, diethanolamine, and the bpe divergent ligand yields a 1-D coordination

Figure 1. View of the binuclear node in compound 1, along with the atom numbering scheme. Table 2. Selected Bond Distances (Å) and Angles (deg) for 1 distances Cu1 O2 Cu1 O2 Cu1 N1 Cu1 N2 Cu1 O1

angles 1.918(3) 1.922(3) 1.981(3) 2.008(3) 2.454(1)

N1 Cu1 O1 O1 Cu1 N2 N2 Cu1 O2 O2’ Cu1 O2 O2 Cu1 N1 N1 Cu1 O2 O2’ Cu1 O1 N1 Cu1 N2 O2’ Cu1 N2

91.73(13) 78.76(13) 84.30(13) 77.99(11) 98.38(12) 166.44(13) 99.96(11) 100.04(14) 161.55(13)

polymer constructed from centrosymmetric binuclear nodes, [Cu2(Hdea)2]2+, and linear spacers (Figure 1). There are also uncoordinated bpe molecules in the crystal. The Cu‚‚‚Cu separation within a node is 2.984 Å, while the distance between the copper(II) ions bridged by the bpe ligand is 13.308 Å. Each copper(II) ion within a node displays a slightly distorted square pyramidal geometry. The basal plane is formed by two alkoxo oxygen atoms, one amino nitrogen, and one nitrogen atom from the bpe ligand. The fifth coordination site is occupied by the oxygen atom from the OH group of the amino alcohol [2.454(3) Å]. Selected bond distances and angles are given in Table 2. The percentage of trigonal distortion from square pyramidal geometry is described by the parameter τ, defined as [(θ φ)/60]100, where θ and φ are the angles between the donor atoms forming the plane in a square pyramidal geometry.14 The value of the τ parameter for the coordination polyhedron of copper(II) in 1 is 7.67%. The binuclear nodes are interconnected through centrosymmetric bpe molecules resulting in infinite chains all running in a parallel direction. The uncoordinated bpe molecules bind parallel chains through weak hydrogen bond interactions established between the nitrogen atom and the C-H group from a bridging bpe molecule [N(3)‚‚‚H-C(5) ) 3.279 Å] and between a C-H group and the oxygen atom from the coordinated OH group [C(5)-H‚‚‚O(1) ) 3.415 Å]. Two-dimensional supramolecular layers with rhombic meshes are formed (Figure 2). The closest Cu‚‚‚Cu separation between such chains is 15.737 Å, and the mesh dimensions, which are determined as the distances between the centers of the adjacent binuclear nodes, are 15.584 and 15.866 Å, for nodes connected by coordination and hydrogen bonds, respectively. Such supramolecular nets are stacked in parallel mode with offset. New Example of Inclined 2-D Interpenetration. To obtain a system with a higher dimensionality, we have chosen an amino alcohol with a lower denticity, which leaves free more than one coordination site to the copper ion. Consequently, the copper(II) ion will be

Binuclear Complexes as Nodes

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Figure 2. Packing diagram in crystal 1, showing the supramolecular gridlike layer.

Figure 4. Two views showing the inclined interpenetration mode of the 2-D layers in crystal 2. Table 3. Selected Bond Distances (Å) and Angles (deg) for 2 distances Cu1 N2 Cu1 N3 Cu1 N1 Cu1 O1 Cu1 O1

Figure 3. Fragment of the 2-D coordination polymer in crystal 2, along with the atom numbering scheme.

available for the coordinative interaction with more than one spacer ligand. Indeed, the reaction between copper(II) perchlorate, monoethanolamine, and bpe leads to a 2-D gridlike coordination polymer with binuclear centrosymmetric nodes (Figure 3). The coordination geometry of each copper(II) ion is again square pyramidal. The basal positions are occupied by two oxygen atoms arising from the alkoxo bridges, one nitrogen from the amino group, and one nitrogen from the spacer. The Cu-N distances are slightly longer than the Cu-O ones. The apical position is occupied by the nitrogen atom arising from another spacer molecule [Cu(1)-N(3) ) 2.342 Å]. The value of the τ parameter is 14.63%. The distance between the copper atoms within a node is 3.020 Å. Selected bond distances and angles are gathered in Table 3. The [Cu2(mea)2]2+ cores are interconnected through bpe molecules, resulting in gridlike layers. The metric of the grid cell is determined by the distances between the centers of symmetry located in the middle of the

angles 1.990(2) 2.342(6) 2.016(2) 1.933(17) 1.921(7)

O1 Cu1 O1 O1 Cu1 N1 N1 Cu1 N3 N2 Cu1 N3 O1’ Cu1 N2 O1’ Cu1 N3 O1’ Cu1 N1 O1 Cu1 N2 O1 Cu1 N3 N2 Cu1 N1

76.85(9) 83.42(10) 94.18(12) 98.44(10) 96.54(9) 100.87(10) 156.24(11) 165.02(9) 96.02(9) 99.33(11)

copper nodes: 14.548 and 15.584 Å. The distances between the copper ions bridged by bpe ligands in the mesh are 13.381 and 14.051 Å. This difference in Cu‚‚ ‚Cu separations roughly corresponds to the double of the difference between the Cu-N distances for the coordination to copper(II) ion by bpe exo-ligands in the basal plane and in the apical position. The most interesting feature of the solid-state architecture of 2 consists of its interlocked 3-D structure, resulting from the inclined interpenetration of the gridlike sheets. Every mesh of every sheet contains parts of two others passing through it (Figure 4). We recall here that a similar 2-D gridlike coordination polymer has been obtained by reacting copper(II) perchlorate with 4,4′bipy, the amino alcohol being also bidentate (aminopropanol).9 This compound does not display interpenetration. The 2-D coordination networks stack parallel to one another generating channels. The absence of the solvent and of the uncoordinated organic molecules, as well as the superior length of bpe, in comparison with

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4,4′-bipy, favor the interpenetration observed with compound 2. In conclusion, we have illustrated with new examples that alkoxo-bridged copper(II) cationic species are quite versatile building blocks in constructing various solidstate architectures. The denticity of the amino alcohols can be used in tuning the dimensionality of the resulting coordination polymers.

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Acknowledgment. Financial support from the INTAS Program (Project 2000-00375) is gratefully acknowledged. We thank Prof. G. Bocelli, IMEM-CNR Parma, for the X-ray measurements for 2. Supporting Information Available: X-ray crystallographic files in CIF format deposited with the Cambridge Structural Database as files CCDC 232372, 232373, respectively, for crystals 1 and 2. This material is available free of charge via the Internet at http://pubs.acs.org.

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