Self-Assembly of a CsCl-like 3D Supramolecular Network from [Zn6(HL)6(H2L)6]6+ Metallamacrocycles and (H2O)20 Clusters (H2L ) 4-(2-Pyridyl)-6-(4-pyridyl)-2-aminopyrimidine) Yingnan Chi,†,‡ Kunlin Huang,§ Shaowen Zhang,† Fengyun Cui,†,‡ Yanqing Xu,†,‡ and Changwen Hu*,†,‡
CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 12 2449–2453
The Institute for Chemical Physics and Department of Chemistry, Beijing Institute of Technology, Beijing 100081, State Key Labarotory of Explosion Science and Technology, Beijing Institute of Technology, Beijing 100081, and College of Chemistry, Chongqing Normal UniVersity, Chongqing 400047, People’s Republic of China ReceiVed NoVember 4, 2006; ReVised Manuscript ReceiVed September 11, 2007
ABSTRACT: The reaction of Zn(NO3)2 · 6H2O with multifunctional ligand 4-(2-pyridyl)-6-(4-pyridyl)-2-aminopyrimidine (H2L) leads to a circular hexanuclear zinc complex [Zn6(HL)6(H2L)6](NO3)6 · 26H2O (1), confirmed by single-crystal X-ray diffraction. In the [Zn6(HL)6(H2L)6]6+ cation, six zinc centers are arranged in a chairlike conformation and 12 ligands fulfill bridging and terminal functions, respectively. The particular interest of complex 1 is the formation of a unique water cluster (H2O)26 composed of a clathrate (H2O)20 core and six dangling water molecules, and the clathrate (H2O)20 core is structurally similar to the famous “Bucky water” (H2O)20. Furthermore, the water molecules and the nitrate ions are assembled into an interesting negative three-dimensional (3D) framework through hydrogen bonds, and the [Zn6(HL)6(H2L)6]6+ cations just locate in the cavities of the anionic 3D network. To gain insight into the stability of (H2O)20 observed in complex 1, we isolate the water cluster from its environments and compare its stability with “Bucky water” (H2O)20 by a theoretical calculation method. Complex 1 displays room temperature photoluminescence. Introduction The self-assembly process driven by some weak interactions, such as hydrogen bonding (H-bond), π-π stacking, electrostatic and Van der Waals forces, and hydrophobic and hydrophilic interactions, is crucial in the biological world.1 Following the lead of nature, self-assembly in coordination chemistry has become one of the most efficient and widely utilized approaches to construct supramolecular architectures, which exhibit potential applications in catalysis, storage, delivery, molecular magnets, and recognition.2 Currently, various structural motifs, such as grids, racks, ladders, molecular polygons, and polyhedra, have been obtained by self-assembly.3 Among them, metallamacrocycles have attracted a significant amount of attention because of their aesthetically appealing structures and the insight that they give into understanding the self-assembly processes.4 Directional coordination bonds have been utilized to construct metallamacrocycles and to allow the self-assembly process to arrange in a predetermined fashion. For example, four-coordinated Pd(II) or Pt(II) ions fit for the assemblies of molecular squares5 and sixcoordinated Co(II/III), Fe(II/III), Mn(II/III), or Cu(II) ions are used to construct hexanuclear metallamacrocycles.6 In contrast to the metallamacrocycles constructed from the above-mentioned metal ions, the multinuclear Zn(II) rings are relatively rare.7 However, multinuclear zinc systems are important structural motifs and have been implicated in biological systems,8 so the synthesis of multinuclear Zn(II) structures is of great significance. In the past decade, water clusters have become an active research field and have been investigated experimentally and * To whom correspondence should be addressed. Tel: +86-10-68912667. Fax: +86-10-68914780. E-mail:
[email protected]. † The Institute for Chemical Physics and Department of Chemistry, Beijing Institute of Technology. ‡ State Key Labarotory of Explosion Science and Technology, Beijing Institute of Technology. § Chongqing Normal University.
Scheme 1. Two Different Coordination Modes of the H2L Ligand and the Obtained Hexanuclear Zinc Structure
theoretically.9 The studies of water clusters in different environments help us to understand the roles of water clusters in stabilizing and functionalizing some supramolecular species in aqueous solutions.10 Interestingly, in the investigation of water clusters in organic or metal-organic solid-state structures, we found that the discrete (H2O)26 cluster is rarely reported in contrast to the frequently observed water clusters such as (H2O)n (n ) 2-6, 8, 10-12, 14, and 16).11–21 The 4-(2-pyridyl)-6-(4-pyridyl)-2-aminopyrimidines (H2L) (Scheme 1) are five-dentate, multifunctional ligands and were first designed and synthesized in our group.22 In the ligand, the existence of both hydrogen-bonding donors (amino group) and acceptors (aromatic N atoms) lays the foundation for the formation of H-bond supramolecular architectures. During the reaction of Zn(NO3)2 · 6H2O with an H2L ligand, a circular hexanuclear zinc complex [Zn6(HL)6(H2L)6](NO3)6 · 26H2O (1) is prepared under hydrothermal conditions and is characterized by IR, X-ray powder diffraction (XPRD), and single-crystal X-ray diffraction. Interestingly, a novel water cluster (H2O)26 composed of clathrate (H2O)20 and six dangling water molecules is formed in the crystal lattice. Furthermore, the discrete hexanuclear zinc ring [Zn6(HL)6(H2L)6]6+, water clusters, and nitrate counteranions are assembled into a
10.1021/cg0607809 CCC: $37.00 2007 American Chemical Society Published on Web 11/03/2007
2450 Crystal Growth & Design, Vol. 7, No. 12, 2007
Chi et al.
Table 1. Crystallographic Data for Complex 1a formula Fw a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) space group crystal system reflns. collected a
R3j
unique reflns. Dcalcd volume µ F(000) Z crystal size (nm3) temperature (K) gof
0.953
rhombohedral
R1 [I > 2δ(I)]
0.0777
24089
ωR2 (all data)
0.2830
C28H29.67N11O7.33Zn 4217.98 16.931(4) 16.931(4) 16.931(4) 95.340(4) 95.340(4) 95.340(4)
5559 1.463 4786.4(19) 0.834 2180 6 0.25 × 0.21 × 0.18 298
R1 ) Σ||F0| - |Fc||/Σ|F0| and wR2 ) Σ w(F02 - FC2)2]/Σ[w(F02)2]1/2.
novel CsCl-like 3D supramolecular structure via electrostatic and H-bond interactions.
Table 2. Hydrogen Bonds in 1a D-H · · · A N3-H3A · · · N3 (1#) N3-H3A · · · N8 N3-H3B · · · N3 (2#) N8-H8 · · · N3 (1#) N8-H8 · · · N1 (1#) O4-H29 · · · N5 (3#) O4-H30 · · · O7 O5-H31 · · · O4 (4#) O6-H32 · · · O4 O6-H33 · · · O8 O7-H34 · · · O4 O7-H35 · · · O6 (5#) O8-H36 · · · O3 (6#) O8-H37 · · · O1
D-H (Å) H · · · A (Å) D · · · A (Å)
