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

Abstract

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 Fe(III) core to Fe(II) generates complexes that feature heteropolycations in which ferrocyanide is encapsulated by the Cu(II) 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 P2(1)/c (#14) with a = 14.8674(10), b = 25.9587(10), c = 27.5617(10) A, beta = 100.8300(10) degrees, 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) A, alpha = 110.750(3), beta = 90.206(2), gamma = 112.754(3) degrees, 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.

Hexacyanometalate Molecular Chemistry: Di‐, Tri‐, Tetra‐, Hexa‐ and Heptanuclear Heterobimetallic Complexes; Control of Nuclearity and Structural Anisotropy

“…[18] Despite our endeavors, until now we have not isolated single crystals suitable for X-ray crystallography.…”

Two-dimensional coordination compounds based on Fe(II) and Co(III) hexacyanometallates with Cu(II)(dien) groups: Structures and magnetic properties

“…The fit could be improved by slightly increasing the g-value, but the increase is within the experimental error. More examples are known of diamagnetic hexacyanometallate bridges where the Cu-N bond involves the Cu(II) d z 2 orbital, e.g., Cu(II)-NC-Fe(II) [18] or Cu(II)-NC-Co(III) [6d]. For such bridges weak antiferromagnetic couplings are reported, e.g., Cu(II)-NCFe(II) with J = À0.73 cm À1 [6f] or Cu(II)-NC-Co(III) with J = À0.82 cm À1 [6d] and J = À0.81 cm À1 [6f], which are comparable to our value of 2J = À0.79 cm À1 for 1.…”

Structure and magnetism of heptanuclear complex constructed by the encapsulation of octacyanotungstate(IV) with copper(II) cations of tripodal ligands

“…The geometry of copper ions could be best described as a distorted trigonal bipyramid with the equatorial N atoms from three pyridinate rings of TPA ligands and axial N atoms containing aliphatic N atom and cyano N atom. The values of N(py)\Cu\N(cyano) angles are much larger than the ones of N(py)\Cu\N(amine) because of the steric effect caused by the five-membered chelate rings [11]. Further, the whole bimetallic heptanuclear cation is surrounded by eight perchlorate anions, which are located in the cavity of the adjacent cations.…”