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

A series of complexes containing [MLx]Cl2 (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. [ML2(μ-Cl)2Hg(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)Cl2(μ-Hg(CN)2)] (5)
is an alternating 1-D chain of Cu(terpy)Cl2 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)2Cl]2Hg(CN)2[Hg(CN)2Cl]2} (6), an alternating 1-D chain of [Hg(CN)2Cl]22- dimers that are N-bound
to Hg(CN)2 units that also bind to dangling [Cu(phen)2Cl]+ moieties. In [Cu(dien)Cl][Hg(CN)2Cl] (7), 1-D chloride
bridged [Hg(CN)2Cl]nn- double salt chains formed in situ during polymer formation are held in place by chloride
bridged [Cu(dien)Cl]22+ 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)2Cl][HgX2Cl] (8). N-cyano coordination and chloride bridging from Hg(CN)2 and chloride ligands in {[Ni(tren)]4[Hg(CN)2]8Cl6}HgCl4 (9) generate 1-D cationic columns of {[Ni(tren)]4[Hg(CN)2]8Cl6}n2n+ which hydrogen bond to
tetrahedral [HgCl4]2- moieties, increasing the structural dimensionality of this noncentrosymmetric complex. Factors
influencing the structural dimensionality and the induction of N-cyano bridging are discussed.