Encapsulation of Cyanometalates by a Tris‐macrocyclic Ligand Tricopper(II) Complex: Syntheses, Structural Variation, and Magnetic Exchange Coupling Pathways

Abstract

The reaction of [M(CN)(6)](3-) (M = Cr(3+), Mn(3+), Fe(3+), Co(3+)) and [M(CN)(8)](4-/3-) (M = Mo(4+/5+), W(4+/5+)) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu(3)(L)](6+)) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu(3)(L)](6+) forms the isostructural host-guest complexes [[[Cu(3)(L)(OH(2))(2)][M(CN)(6)](2)][M(CN)(6)]][M(CN)(6)]30 H(2)O with one bridging, two partially encapsulated, and one isolated [M(CN)(6)](3-) unit. The octacyanometalates of Mo(4+/5+) and W(4+/5+) are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)(8)](4-) were obtained. The Mo(4+) and W(4+) complexes were crystallized in two different structural forms: [[Cu(3)(L)(OH(2))](2)[Mo(CN)(8)]](NO(3))(8)15 H(2)O with a structural motif that involves isolated spherical [[Cu(3)(L)(OH(2))](2)[M(CN)(8)]](8+) ions and a "string-of-pearls" type of structure [[[Cu(3)(L)](2)[M(CN)(8)]][M(CN)(8)]](NO(3))(4) 20 H(2)O, with [M(CN)(8)](4-) ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the CuCu pairs in the [Cu(3)(L)](6+) "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr(3+), exchange coupling of Mn(3+) and Fe(3+) is very small, and the octacoordinate Mo(4+) and W(4+) systems have a closed-shell ground state.

Tuning of Inter- versus Intrachain Magnetic Interactions in Cyano-Bridged NiII/MIII (M = Cr, Fe, Co) Chain Complexes

“…Experimental and theoretical studies show, however, that Jahn−Teller instabilities in cyanide complexes with T ground states are very weak. Indeed, it was possible to simulate the magnetic susceptibility of [Fe(CN) 6 ] 3- ( 2 T 2g , t 2g 5 ) and [Mn(CN) 6 ] 3- ( 3 T 1g , t 2g 4 ) using cubic symmetry . Unlike [Mn(CN) 6 ] 3- , however, the χ T value of [Fe(CN) 6 ] 3- shows a weak dependence on temperature and could be modeled reasonably well, using an s = 1/2 pseudo-pin approach, with an effective g value of about 3.00 (see Figure b).…”

Bispidine Coordination Chemistry

“…These studies were based on melamine-derived mono-, bis-, and tris-macrocyclic copper(II) and nickel(II) complexes and their host-guest compounds with cyanometalates (341)(342)(343)(344)(345). Magnetic exchange through the cyano bridge was shown to lead to multivarious effects and based on a thorough interpretation, there is the possibility to tune the magnetic properties of heterooligonuclear complexes (345,346).…”

DFT Studies on the Magnetic Exchange Across the Cyanide Bridge

“…Recently, we have prepared and characterized a series of oligonuclear cyanometalates . They include Cu II coordinated to four sp 3 -nitrogen atoms from a tetraazamacrocyclic ligand and M III (CN) 6 3- (M III = Cr III (d 3 ) and low-spin Mn III (d 4 ) and Fe III (d 5 ) complexes).…”