PAPER www.rsc.org/dalton | Dalton Transactions Systematic investigation on the coordination chemistry of a sulfonated monoazo dye: Ligand-dominated d- and f-block derivatives† Jian L¨ u, a Shui-Ying Gao, a Jing-Xiang Lin, a Lin-Xi Shi, a Rong Cao* a and Stuart R. Batten b Received 26th August 2008, Accepted 26th November 2008 First published as an Advance Article on the web 28th January 2009 DOI: 10.1039/b814774d Ten coordination compounds based on a sulfonated monoazo dye, formulated as M(H 2 O) 2 (4,4¢-abs) 2 (M = Mn 3a, Co 3b, Cu 3c, Zn 3d, Cd 3e and Pb 3f; 4,4¢-abs = 4-aminoazobenzene-4¢-sulfonic anion), Ag(4,4¢-abs) (4), [Ln(H 2 O)(phen) 2 (4,4¢-abs) 3 ]·3H 2 O (Ln = Gd 5a, Tb 5b, and Ho 5c; phen = 1,10-phenanthroline), as well as the parent ligand L (1) [(4,4¢-Habs) 2 ·4H 2 O] and precursor NaL·HL (2) [Na(4,4¢-abs)(4,4¢-Habs)] were successfully isolated. Structural analyses revealed that the structures of compounds 3a–3f, 4, and 5a–5c vary according to the coordination geometries of the metal ions, and vary from double-strand chain structures (3a–3f) to a 3-D pillared-layer framework (4) to mononuclear complexes (5a–5c). The double-strand chain structures of 3a–3f are isostructural, and are built on octahedral metal centers and double bridging 4,4¢-abs ligands coordinating via terminal N- and O-donors. The silver-containing compound 4 displays a pillared-layer structure constructed from 4.8 2 silver sulfonate nets pillared by the linear backbones of 4,4¢-abs ligands. Compounds 5a–5c, which are also isostructural, possess mononuclear structures consisting of a metal cation, three 4,4¢-abs anions, two auxiliary phen ligands, one aqua ligand and three non-coordinated water molecules. Evidence on two series of isostructural compounds indicates that structures of d- and f-block metal derivatives are dominated by the coordination mode of the ligands. The surface chemistry of compound 5c has been investigated based on the LBL (layer-by-layer) technique. The as-synthesized multilayer films with different composite components exhibit different surface behaviours. Introduction Crystal engineering, a vigorous technique receiving widespread interest from chemists and material scientists, has becoming a flourishing research area in respect to the design of coordination polymers (CPs) by means of effective control over the self-assembly processes. 1–3 With the development of crystal engineering, ra- tional design of coordination polymers on a fundamental level is now possible by means of the elaborate choice of metals and organic ligands, 4 although prediction of the precise solid- state structure remains a long-term challenge owing to some unpredictable elements. 5 Factors such as reaction conditions (pressure, temperature, pH, or light), solvents, template molecules, and auxiliary ligands have been proven to have a great influence on framework structures. 6 Furthermore, previous research on the possible correlation between structure and function, 7, 8 which is greatly advanced through the concept of secondary building units (SBUs), 1–4, 7,8 made it promising and attractive to realize desired functional materials by tuning the crystal structures. As a result, considerable current research effort has been intensively focused on the deliberate use of functional ligands or metals which a State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fujian, Fuzhou 350002, China. E-mail: rcao@fjirsm.ac.cn; Fax: (+86) 591-8379-6710 b School of Chemistry, Monash University, Clayton, Victoria 3800, Australia † Electronic supplementary information (ESI) available: Table of H-bonds, UV-vis spectra, XRPD, AFM images, and crystallographic data. CCDC reference numbers 682495–682505. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b814774d will generate practical materials with potential applications in a number of chosen fields. 9 Azo dyes, an important class of elements in pigment indus- tries, have recently been put forward in coordination chemistry as a burgeoning research target in view of the fact that the physical properties of pigments rest not solely with their molec- ular structures but also significantly with their intermolecular interactions, 10–12 and the structural importance of these interac- tions is of considerable interest in the area of crystal engineering. In this regard, investigations probing into the packing patterns of their coordination compounds and exploration of the structural motifs of azo colorant derivatives are of great significance. Recently, some metal complex dyes have found applications in high-technology realm 12 and the structures of those complexes were identified by analytical and spectroscopic methods. 13 It should be noted that most commercially available pigments are designed to be highly insoluble and, as a consequence, are inappropriate to form high quality single crystals suitable for X-ray diffraction. 11 Therefore, there is a dearth of crystallographic information about their detailed coordination behavior at present. However, sulfonated azo dyes, which represent a subclass of colorants modified with RSO 3 - groups to become more soluble and less toxic, 11 are promising candidates to isolate crystalline solids. Furthermore, RSO 3 - groups are long known as excellent candidates to construct supramolecular compounds thanks to their noticeable abilities in forming coordinative and hydrogen bonds. 14 Hence sulfonated azo dyes might be feasible choices for connecting crystallographic coordination chemistry and colorant chemicals. 1944 | Dalton Trans., 2009, 1944–1953 This journal is © The Royal Society of Chemistry 2009