Tuning the Structures of Mercury Cyanide-Based Coordination Polymers with Transition Metal Cations

Abstract

A series of complexes containing [ML x ]Cl 2 (M = Mn, Cu, Ni; L = 2,2‘-bipyridine (bipy), 1,10-phenanthroline (phen), 2,2‘:6‘,6‘ ‘-terpyridine (terpy), diethylenetriamine (dien), tris(2-aminoethyl)amine (tren); x = 1 or 2) and linear, neutral Hg(CN) 2 building blocks have been synthesized and structurally characterized. In general, the Lewis acidic Hg(CN) 2 moieties accept chloride ligands from the M(II) centers, in several cases increasing the structural dimensionality of the system as a result. [ML 2 (μ-Cl) 2 Hg(CN) 2 ] (M = Mn, Ni; L = bipy, phen) ( 1 − 4 ) are molecular complexes in which the chloride ligands bridge the M(II) and mercury(II) centers; π···π stacking between the aromatic rings from different molecules increases the structural dimensionality. [Cu(terpy)Cl 2 (μ-Hg(CN) 2 )] ( 5 ) is an alternating 1-D chain of Cu(terpy)Cl 2 and Hg(CN) 2 moieties in which the chloride ligands bridge to different mercury(II) centers. When two phen ligands are used with copper(II), an additional Hg(CN) 2 unit is incorporated to form {[Cu(phen) 2 Cl] 2 Hg(CN) 2 [Hg(CN) 2 Cl] 2 } ( 6 ), an alternating 1-D chain of [Hg(CN) 2 Cl] 2 2- dimers that are N-bound to Hg(CN) 2 units that also bind to dangling [Cu(phen) 2 Cl] + moieties. In [Cu(dien)Cl][Hg(CN) 2 Cl] ( 7 ), 1-D chloride bridged [Hg(CN) 2 Cl] n n - double salt chains formed in situ during polymer formation are held in place by chloride bridged [Cu(dien)Cl] 2 2+ cationic dimers to form a 2-D brick-wall layer motif. Two 1-D double salt chains, one cationic and one anionic, which hydrogen bond together to form neutral columns are generated in [Cu(tren)Hg(CN) 2 Cl][HgX 2 Cl] ( 8 ). N-cyano coordination and chloride bridging from Hg(CN) 2 and chloride ligands in {[Ni(tren)] 4 [Hg(CN) 2 ] 8 Cl 6 }HgCl 4 ( 9 ) generate 1-D cationic columns of {[Ni(tren)] 4 [Hg(CN) 2 ] 8 Cl 6 } n 2 n + which hydrogen bond to tetrahedral [HgCl 4 ] 2- moieties, increasing the structural dimensionality of this noncentrosymmetric complex. Factors influencing the structural dimensionality and the induction of N-cyano bridging are discussed.