Copper benzenedicarboxylate coordination polymers incorporating a long-spanning neutral co-ligand: Effect of anion inclusion and carboxylate pendant-arm length on topology and magnetism Lindsey L. Johnston a , Joseph H. Nettleman a , Maxwell A. Braverman a , Laura K. Sposato b , Ronald M. Supkowski b , Robert L. LaDuca a, * a Lyman Briggs College, Department of Chemistry, E-30 Holmes Hall, Michigan State University, East Lansing, MI 48825, USA b Department of Chemistry and Physics, King’s College, Wilkes-Barre, PA 18711, USA article info Article history: Available online 20 May 2009 Keywords: Copper Carboxylate Imine Coordination polymer Antiferromagnetism abstract Three divalent copper coordination polymers containing aromatic dicarboxylate ligands and the long- spanning tethering imine bis(4-pyridylmethyl)piperazine (bpmp) have been prepared and structurally characterized. The length of the dicarboxylate pendant arms, carboxylate binding mode, and the inclusion of anionic components play a synergistic role in structure direction in this system. {[Cu(ip)(bpm- p)(H 2 O)]5H 2 O} n (ip = isophthalate, 1) displays neutral (4,4) rectangular coordination polymer grids that stack in an ABCD repeat pattern. Use of the longer pendant arm dicarboxylate 1,3-phenylenediacetate (phda) resulted in {[Cu 2 (phda) 2 (bpmp)]H 2 O} n (2), a 3-D network coordination polymer with primitive cubic topology that features strongly antiferromagnetically coupled (J = 331(1) cm 1 ) {Cu 2 (CO 2 ) 4 } pad- dlewheel units. In the presence of excess nitrate ions, {[Cu(phda)(Hbpmp)](NO 3 )3H 2 O} n (3) was isolated instead of 2; 3 manifests cationic 2-D coordination polymer layers built from weakly antiferromagneti- cally coupled (J = 2.43(1) cm 1 ) {Cu 2 O 2 } dimers linked through phda and protonated bpmp ligands. The striking difference in magnetic properties is ascribed to the equatorial–equatorial versus axial–equa- torial bridging of copper coordination spheres in 2 and 3, respectively. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Investigation into the synthesis and design of coordination polymers remains an intense research focus because of their utility in various applications such as gas storage [1], small molecule sep- aration [2], ion-exchange [3], catalysis [4], luminescence [5] and non-linear optical devices [6]. Dicarboxylate ligands are among the most commonly used tethering ligands in coordination poly- mer synthesis, providing the necessary charge balance and scaf- folding for the formation of neutral frameworks. A wide variety of structural topologies can occur in these dicarboxylate-based phases, with different metal coordination environments and di- verse carboxylate binding and bridging modes. Although a plethora of divalent metal coordination polymers have been constructed using rigid aromatic dicarboxylates, aliphatic a,x-dicarboxylate li- gands have also proven advantageous because of their ability to adopt different conformations during self-assembly [7–8]. Less commonly studied are coordination polymers built from dicarbox- ylate ligands that possess both rigid aromatic and flexible aliphatic character, such as phenylenediacetate isomers [9–11]. The structural diversity and functional behavior of dicarboxyl- ate-containing coordination polymers has been developed further by the inclusion of neutral nitrogen-base co-ligands, such as the ri- gid-rod tether 4,4 0 -bipyridine (4,4 0 -bpy) [12–15]. One especially intriguing example is the interpenetrated three-dimensional (3- D) phase [Zn(terephthalate)(4,4 0 -bpy) 0.5 ] n , which possesses high thermal robustness and uniquely-shaped cavities that allow the chromatographic separation of linear and branched alkanes [15]. Recently our group has been investigating the preparation and characterization of dual-ligand coordination polymers containing the long-spanning, hydrogen-bonding capable diimine bis(4-pyri- dylmethyl)piperazine (bpmp, Scheme 1). Its greater girth and supramolecular points of contact, absent in 4,4 0 -bpy, have pro- moted the generation of coordination polymers with unique topol- ogies [16–19]. For instance, {[Cd(succinate)(bpmp)(CH 3 OH) 2H 2 O} n manifests a chiral coordination polymer layered structure with an unprecedented 6 5 8 topology, fostered by the length mis- match between the two ligands [16]. [Co 3 (oxybisbenzo- ate) 3 (bpmp) 2 ] n possesses a unique self-penetrated 8-connected topology built from the interlocking of three types of homochiral helical motifs, linked throughout by bpmp ligands [17]. In this con- tribution we report the synthesis and structural characterization of three copper aromatic meta-dicarboxylate coordination polymers 0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2009.05.022 * Corresponding author. Tel.: +1 5174322268. E-mail address: laduca@msu.edu (R.L. LaDuca). Polyhedron 29 (2010) 303–311 Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly