www.elsevier.nl/locate/inoche Inorganic Chemistry Communications 3 (2000) 93–95
A dimer structure {[Cu(phen)2Cl][OH]P6H2O}2 constructed through C–H∆Cl hydrogen bondings and p–p interactions Bao-Qing Ma, Song Gao *, Tao Yi, Chun-Hua Yan, Guang-Xian Xu State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, PR China Received 14 January 2000
Abstract The first near regular trigonal bipyramid [Cu(phen)2Cl]q type compound has been synthesized, which possesses a dimer structure constituted through C–H∆Cl hydrogen bondings and p–p interactions between phen rings. q2000 Elsevier Science S.A. All rights reserved. Keywords: Crystal structures; Copper(II) complexes; Hydrogen bonding; p–p Stacking
The structural pathways of the five coordination CuN4X (XsCl, H2O; N4sphen, bipy) chromophore have been substantially investigated [1–3]. They can find application in predicting the electronic properties of corresponding complexes of known structures [4] and the structure of related complexes from a knowledge of their electronic properties, such as under pressure or after heating [5–7]. This kind of structure–property relationship is established on the basis of numerous structural data. Compared with [Cu(bipy)2Cl]q compounds, the structurally characterized [Cu(phen)2Cl]q compounds are relatively limited [1–3]. In this work, the structure of [Cu(phen)2Cl][OH]P6H2O, very similar to that of [Cu(bipy)2Cl][OH]P6H2O [8], will be reported. More interestingly, the mononuclear units of [Cu(phen)2Cl]q were connected via C–H∆Cl hydrogen bondings and p–p interactions giving rise to a dimer structure [Cu(phen)2Cl]2[OH]2P12H2O. Although the C–H∆X (XsO, Cl, N, etc.) interactions were confirmed from spectroscopic and crystallographic evidence [9,10], they have usually been ignored and even denied in the past [11]. Until recently, much attention was paid to weak hydrogen bondings in the field of structural chemistry and biology owing to their importance in crystal packing [12], molecular recognition [13,14], the stability of inclusion complexes [15–17], and the activity of biological macromolecules [18,19]. Numerous experiments have been performed and several reviews * Corresponding author. Tel.: q86 10 62754179; fax: q86 10 62751708; e-mail:
[email protected]
have been documented for C–H∆O interactions [20–22], whereas C–H∆Cl interactions are rarely studied [23]. Recently, Aakeroy et al. demonstrated the existence and universality of C–H∆Cl hydrogen bonding using a statistical analysis method on exacted data from the CSD [24]. The title compound provides a unique case of a dimeric unit formed through this kind of weak hydrogen bonding. To a hot solution of CuCl2P2H2O (1 mmol) in 20 ml water, phen (2 mmol) dissolved in 20 ml ethanol was added and heating was continued under stirring. 0.1 M NaOH was used to adjust the pH to 6. The resulting solution was filtered and the filtrate was allowed to stand at room temperature. After 2 weeks, blue prismatic single crystals were obtained. An X-ray diffraction analysis [25] revealed that the compound consists of one discrete [Cu(phen)2Cl] cation, one free OHy anion and six solvent water molecules. The Cu(II) is five coordinated by two chelated phen rings intersecting at 51.50(0.08)8 and one chloro atom. According to the law summarized by Hathaway and co-workers for this series of compounds [1–3], the t value of this compound is 0.91. Its geometry may be described as a near regular trigonal bipyramid (RTB). Most of the t values for the [Cu(phen)2Cl]q series of compounds studied previously fall in the range 0.81– 0.56 and the stereochemistries are best regarded as a square based pyramidal distortion. One exception with ts0.19 forms a trigonal bipyramidal distorted square based pyramidal stereochemistry. Unlike the [Cu(bipy)2Cl]q series, in which there are several examples possessing RTB geometry, no compounds having a near RTB geometry for this series
1387-7003/00/$ - see front matter q2000 Elsevier Science S.A. All rights reserved. PII S 1 3 8 7 - 7 0 0 3 ( 0 0 ) 0 0 0 1 6 - 2
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Fig. 1. Dimer structure [Cu(phen)2Cl]22q formed by C–H∆Cl hydrogen ˚ and angles (8): bondings and p–p interactions. Selected bond lengths (A) Cl(1)–Cu(1)s2.3330(19), Cu(1)–N(1)s1.975(5), Cu(1)–N(4)s 1.979(5), Cu(1)–N(3)s2.085(5), Cu(1)–N(2)s2.106(5), N(1)– Cu(1)–N(4)s176.2(2), N(1)–Cu(1)–N(3)s94.7(2), N(4)–Cu(1)– N(3)s81.8(2), N(1)–Cu(1)–N(2)s81.7(2), N(4)–Cu(1)–N(2)s 99.2(2), N(3)–Cu(1)–N(2)s122.97(18), N(1)–Cu(1)–Cl(1)s 90.94(16), N(4)–Cu(1)–Cl(1)s91.95(16), N(3)–Cu(1)–Cl(1)s 121.51(13), N(2)–Cu(1)–Cl(1)s115.46(14).
have been found. The title compound shows the first RTB ˚ case for the phen series. The Cu–Cl bond length is 2.3330 A, significantly longer than those found in other [Cu(phen)2Cl]q compounds and close to the values observed in RTB bipy compounds. The out-of-plane Cu1–N1 and Cu1–N4 bond ˚ respectively, shorter than lengths are 1.9754 and 1.9788 A, the in-plane Cu1–N2 and Cu1–N3 bond distances (2.0854 ˚ respectively). These observations are consisand 2.1058 A, tent with its near RTB stereochemistry. A striking feature of this compound resides in its binuclear structure formed through C–H∆Cl hydrogen bonding and p–p interactions as depicted in Fig. 1. The H atoms of the phen ring have been activated by the positive charge on the mononuclear cation unit [Cu(phen)2Cl]q and the donation electron trend of phen on the metal ion due to coordination of the N atoms. At a suitable distance and hindrance, it has a tendency to yield weak hydrogen bonding with neighboring O or X atoms. In this case, the Cl atom of a neighboring molecule functions as the hydrogen bonding donor. Thus, two mononuclear units are connected by two symmetry equivalent C–H∆Cl hydrogen bondings leading to a dimer structure. Does the C–H∆Cl hydrogen bonding really exist?
In fact, this has been contested on weak interactions such as C–H∆X (O, Cl, N, p). However recently, a wave of interest in weak hydrogen bonding has emerged in different fields and it is now widely accepted. Strong evidence for the formation of C–H∆Cl hydrogen bonding was provided in a recent paper [24]. A statistical analysis based on CSD suggests that the C–H∆Cl contact is within the range 2.7–3.0 ˚ In this case, the C–H∆Cl distance is 2.772 A, ˚ falling into A. this range. Furthermore, the C–H«Cl bond angle of 157.38 has pronounced directionality. These facts clearly indicate that the C–H∆Cl interactions possess features of hydrogen bonding. Meanwhile, two phen rings are parallel to each other and cause significant p–p stacking. The center-to-center and interplanar distances between the two phen planes are 3.931 ˚ respectively [26]. The two kinds of interacand 3.4376 A, tions mutually strengthen and solidify the dimer moiety. One of the phen rings in the [Cu(phen)2Cl]q cation participates in the formation of the dimer unit via p–p interactions. The remaining one also produces p–p interactions between dimers as shown in Fig. 2. The center-to-center and ˚ respectively. interplanar distances are 3.675 and 3.4216 A, Thus, the binuclear [Cu(phen)2Cl]22q units are linked to each other in 3D space. The crystal lattice water molecules and hydroxyl groups are involved in the hydrogen bonding network, making the system stable. In summary, with the current interests in crystal engineering and supramolecular chemistry, there is now a new insight into weak hydrogen bonding interactions. The title compound offers a good example of C–H∆Cl hydrogen bonding. The dimer structure constructed through C–H∆Cl hydrogen bonding and p–p interactions is also unique. In addition, it is the first case of a near regular trigonal bipyramid for the [Cu(phen)2Cl]q series of compounds. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No. 29771001 and 29831010), the National Key Project for Fundamental
Fig. 2. The packing diagram of [Cu(phen)2Cl]22q units (water molecules are omitted for clarity).
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Research and Founder Corporation Group Foundation of Peking University.
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