The Encapsulation of Ferrocyanide by Copper(II) Complexes of Tripodal Tetradentate Ligands. Novel H-Bonding Networks Incorporating Heptanuclear and Pentanuclear Heterometallic Assemblies

Substitution of the weakly binding aqua ligand in [Cu(tren)OH2]2+ and [Cu(tpa)OH2]2+ (tren = tris(2-aminoethyl)amine; tpa = tris(2-pyridylmethyl)amine) by a cyano ligand on ferricyanide results in the assembly of
heteropolynuclear cations around the cyanometalate core. In water, the reduction of the FeIII core to FeII generates
complexes that feature heteropolycations in which ferrocyanide is encapsulated by the CuII moieties:  [{Cu(tpa)CN}6Fe][ClO4]8·3H2O 1, [{Cu(tren)CN}6Fe][ClO4]8·10H2O 2, [{Cu(tren)CN}6Fe][Fe(CN)6]2[ClO4]2·15.8H2O 3,
and [{Cu(tren)CN}6Fe][{Cu(tren)CN}4Fe(CN)2][Fe(CN)6]4·6DMSO·21H2O 4. The formation of discrete molecules,
in preference to extended networks or polymeric structures, has been encouraged through the use of branched
tetradentate ligands in conjunction with copper(II), a metal center with the propensity to form five-coordinate
complexes. Complex 3 crystallizes in the monoclinic space group P21/c (#14) with a = 14.8674(10), b =
25.9587(10), c = 27.5617(10) Å, β = 100.8300(10) °, and Z = 4, and it is comprised of almost spherical
heptanuclear cations, [{Cu(tren)CN}6Fe]8+, whose charge is balanced by two ferricyanide and two perchlorate
counteranions. Complex 4 crystallizes in the triclinic space group P1 (# 1) with a = 14.8094(8), b = 17.3901(7),
c = 21.1565(11) Å, α = 110.750(3), β = 90.206(2), γ = 112.754(3) °, and Z = 1, and it is comprised of the
heptanuclear [{Cu(tren)CN}6Fe]8+ cation and pentanuclear [{Cu(tren)CN}4Fe(CN)2]4+ cation, whose terminal
cyano ligands are oriented trans to each other. The charge is balanced exclusively by ferricyanide counteranions.
In both complexes, H-bonding interactions between hydrogens on primary amines of the tren ligand, terminal
cyano groups of the ferricyanide counterions, and the solvent of crystallization generate intricate 3D H-bonding
networks.