PAPER www.rsc.org/dalton | Dalton Transactions Supramolecular ‘flat’ Mn 9 grid complexes—towards functional molecular platforms†‡ Victoria A. Milway, a S. M. Tareque Abedin, a Virginie Niel, a Timothy L. Kelly, a Louise N. Dawe, a Subrata K. Dey, a David W. Thompson, a David O. Miller, a Mohammad Sahabul Alam, b Paul M¨ uller b and Laurence K. Thompson* a Received 8th November 2005, Accepted 27th January 2006 First published as an Advance Article on the web 12th May 2006 DOI: 10.1039/b515801j Flat, quantum dot like arrays of closely spaced, electron rich metal centres are seen as attractive subunits for device capability at the molecular level. Mn(II) 9 grids, formed by self-assembly processes using ‘tritopic’ pyridine-2,6-dihydrazone ligands, provide easy and pre-programmable routes to such systems, and have been shown to exhibit a number of potentially useful physical properties, which could be utilized to generate bi-stable molecular based states. Their ability to form surface monolayers, which can be mapped by STM techniques, bodes well for their possible integration into nanometer scale electronic components of the future. This report highlights some new Mn(II) 9 grids, with functionalized ligand sites, that may provide suitable anchor points to surfaces and also be potential donor sites capable of further grid elaboration. Structures, magnetic properties, electrochemical properties, surface studies on HOPG (highly ordered pyrolytic graphite), including the imaging of individual metal ion sites in the grid using CITS (current imaging tunneling spectroscopy) are discussed, in addition to an analysis of the photophysics of a stable mixed oxidation state [Mn(III) 4 Mn(II) 5 ] grid. The grid physical properties as a whole are assessed in the light of reasonable approaches to the use of such molecules as nanometer scale devices. Introduction Molecular construction techniques for coordination complexes have evolved from the simple starting point of mixing solutions of a ligand and metal ion, and taking a chance on the outcome, to the point where some predictability can be built into the reaction by pre-programming of the ligand itself. This does not come about initially by design, but usually follows a sequence of events where rational observations on reaction outcomes reveal the reaction secrets. Self-assembly methods play a pivotal role in biological chemistry, where subtle intermolecular forces can lead to the organization of molecular precursors, in order to facilitate important chemical processes. It is in the spirit of this molecular pre-arrangement that self-assembly methods have found an important role in synthetic coordination chemistry, where rational approaches to the synthesis of desired products are required. The ligand can express the outcome of a reaction with a metal ion if it takes into account the coordination preferences a Department of Chemistry, Memorial University, St. John’s, Newfoundland, A1B 3X7, Canada. E-mail: lthomp@mun.ca; Fax: +1-709-737-3750 b Physikalisches Institut III, Universit¨ at Erlangen-N¨ urnberg, D-91058, Er- langen, Germany †Based on the presentation given at Dalton Discussion No. 9, 19–21st April 2006, Hulme Hall, Manchester, UK. ‡ Electronic supplementary information (ESI) available: Fig. S1 (structural representation of cation 4), Fig. S2 (magnetic data (l mol /T ) for complex 5), Fig. S3 (magnetic data (v mol /T , l mol /T ) for complex 7), Fig. S4 (M/H at 2 K for complex 7), Fig. S5 (p–p contacts in 10), Fig. S6 (extended p–p and NH 2 –NH 2 contacts in 10), Fig. S7 (UV data on 8, 9); Table S1 (Band I and II analysis for 9). See DOI: 10.1039/b515801j of the particular metal. Lehn et al . described this in terms of the ‘coordination algorithm’. 1 In essence one builds compartments or pockets into the ligand with desired donor arrangements, and places these pockets in strategic locations along the ligand backbone. Substituted pyrimidines (see for example Chart 1a) have been particularly successful in this context, 2,3 leading to the formation of ‘ditopic’ ligands, which self assemble to form tetra-nuclear [2 × 2] grid complexes with a variety of metal ions. 3 Extended ligand systems in this class have also produced grids with much higher nuclearity, with up to 16 metals in [4 × 4] arrays in the case of lead. 4 Property–structure relationships are critical in terms of the design of a ligand, and within a multi-metallic assembly remote positioning of paramagnetic metal ions does not encourage intramolecular spin communication or lead to novel electronic properties. Small bridging groups (e.g. oxygen), capable of prop- agating efficient spin exchange between metal ions are important in this context, and bring the metal ions into close proximity when strategically located in a ligand framework. Substituted amidrazone ligands like poap (ditopic) and 2poap (tritopic) and their variants (Chart 1b) are ideally suited for this purpose, and self-assemble in high yield in the presence of a variety of metal ions (e.g. Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II)) to produce tetra-nuclear [2 × 2] 5,6 and nona-nuclear [3 × 3] grids (Scheme 1) respectively. 7–17 The metal ions are held in close proximity within the grid framework by deprotonated hydrazone oxygen bridging atoms, with metal–metal separations of ∼4A ˚ . This leads to intramolecular exchange coupling with all copper(II) examples exhibiting ferromagnetic exchange and all others antiferromagnetic exchange. This journal is © The Royal Society of Chemistry 2006 Dalton Trans., 2006, 2835–2851 | 2835