New Cyanometalate Building Units: Synthesis and Characterization of [Re(CN)₇]^3- and [Re(CN)₈]^3-

Abstract

Two new cyanorhenate complexes of potential utility in constructing magnetic and photomagnetic materials are reported. Reaction of (Bu4N)CN with [ReCl6]2- in acetonitrile affords yellow (Bu4N)3[Re(CN)7] (1), featuring the pentagonal bipyramidal complex [Re(CN)7]3-. The spectral and magnetic properties of 1 indicate that the complex has an S = 1/2 ground state with considerable anisotropy in the g tensor. In aqueous solution, 1 reacts with Mn2+ ions to generate the three-dimensional cyano-bridged solid [fac-Mn(H2O)3][cis-Mn(H2O)2][Re(CN)7].3H2O (2) containing diamagnetic [Re(CN)7]4-. Addition of KIO4 to the reaction solution, originally intended to prevent reduction of the rhenium during solid formation, instead yields white (Bu4N)3[Re(CN)8] (3). As crystallized in K3[Re(CN)8].2MeCN (4.2MeCN), the diamagnetic [Re(CN)8]3- complex adopts a nearly perfect square antiprismatic coordination geometry. In solution, this species behaves analogously to the isoelectronic [M(CN)8]4- (M = Mo, W) complexes, apparently converting to a dodecahedral geometry and photooxidizing under UV radiation to give paramagnetic [Re(CN)8]2-.

Synthesis and Redox‐Induced Structural Isomerization of the Pentagonal Bipyramidal Complexes [W(CN)5(CO)2]3− and [W(CN)5(CO)2]2−

“…[12] In both molecules, the two carbonyl groups were tentatively assigned to the axial sites on the basis of comparisons of thermal ellipsoids, W À C and W···O/N distances, and refinement residual factors. 3À [7] which show no differences between the axial and equatorial bonds within experimental error. For each molecule, the distortion away from a perfect pentagonal bipyramidal coordination of the W II center occurs amongst the cyanide ligands, one of which (the rightmost in Figure 1) is raised above the mean equatorial plane by approximately 108, and one of which (the foremost) is pushed below the plane by 7 ]·H 2 O, and were attributed to crystal packing effects.…”

“…This prediction is indeed borne out in the EPR spectrum of [Re (CN) 7 ] 3À , a species which, unfortunately, is highly unstable to reduction. [7,8] Although the diamagnetic complex [W(CN) 7 ] 5À has been claimed on the basis of spectroscopic data, [9] attempts to reproduce these results led only to mixtures containing [W(CN) 8 ]…”

Assembly of Mn(III) Schiff Base Complexes with Heptacyanorhenate (IV)

“…However, all attempts to prepare low-dimensional (LD) assemblies incorporating [Mn(acacen)] + and pentagonal bipyramidal (PB) geometry [Re(CN) 7 ] 3− failed. Highly magnetically anisotropic heptacyanorhenate(IV) is not commercially available, and may be prepared only as a tetrabutylammonium salt [26]. A combination of the latter with [Mn(acacen)]Cl-regardless of their ratio-led to the neutral 3D framework {[(Mn(acacen)) 3 Re(CN) 7 ]} n that displays nontrivial strongly anisotropic magnetic behavior [14].…”

The First Homoleptic Complex of Seven-Coordinated Osmium: Synthesis and Crystallographical Evidence of Pentagonal Bipyramidal Polyhedron of Heptacyanoosmate(IV)

“…Inspired by a successful ligand exchange preparation of (n-Bu 4 N) 3 [Re IV (CN) 7 ] performed by M.V. Bennett and J.R. Long [36], we have adapted this procedure for the synthesis of osmium cyanides starting from (n-Bu 4 N) 2 Os IV Cl 6 . Indeed, after the addition of the cyanide agent to a cold solution of (n-Bu 4 N) 2 Os IV Cl 6 in dry DMF followed by the heating of the reaction mixture at 100 • C for 16 h, a dark green-bluish solution was obtained (see Experimental Section).…”

“…Only cyanometallates(II) and (III) were structurally characterized to date despite the existence of higher oxidation states for osmium. Moreover, the homoleptic coordination compounds of Os with purely inorganic ligands comprise mainly hexaligated complexes, unlike its nearest neighbor of the 5d row, Re, which demonstrates coordination numbers from six to eight [33][34][35][36]. The recent isolation of heptacyanotungstate(IV) as a salt (n-Bu 4 N) 3 [W IV (CN) 7 ] (n-Bu 4 N = tetra-n-butylammonium) [37] has widened the family of rare heptacyanometallate anions.…”