Trigonal-Bipyramidal Metal Cyanide Complexes: A Versatile Platform for the Systematic Assessment of the Magnetic Properties of Prussian Blue Materials

Abstract

Pentanuclear cyanide-bridged clusters of the general formula {[M(tmphen)(2)](3)[M'(CN)(6)](2)} (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) have been under investigation in our laboratories for a number of years. These related molecules are conveniently prepared by a building block approach that involves the reaction of mononuclear {M(tmphen)(2)X(2)}(0/2+) species (M = Cr, Mn, Fe, Co, Ni, Zn; X = anion, solvent) with [M'(CN)(6)](3-) anions (M' = Cr, Mn, Fe, Co, Os). The resulting trigonal-bipyramidal (TBP) clusters, consisting of M and M' centers in the equatorial and axial positions, respectively, exhibit diverse properties including those that had previously been observed only for Prussian blue extended phases; these properties include single-molecule magnetism, spin crossover, charge-transfer-induced spin transitions, cyanide linkage isomerism, and magnetic coupling through diamagnetic metal ions. Given that a series of clusters with identical axial cyanometallate units can be prepared, we have been able to establish trends in magnetic coupling for families of clusters with different equatorial metal ions. The crystal packing of the clusters, which involves supramolecular pi-stacking interactions, reveals the origin of the observed differences in the coordination environments and, in several cases, the physical properties of the metal ions in the equatorial sites. Recent work has focused on the use of these molecules as building blocks for magnetic chains and the incorporation of highly anisotropic 5d metal ions such as Os(III) into the TBP core. Such comprehensive studies of small clusters are valuable for understanding and modeling the magnetic behavior of more complicated cyanide materials.

Optical Activity and Dehydration-Driven Switching of Magnetic Properties in Enantiopure Cyanido-Bridged CoII3WV2 Trigonal Bipyramids

“…23 The CN − -bridged molecules adopt various discrete topologies controlled by a range of blocking ligands. 24 This includes trinuclear M 2 M′, 25,26 tetranuclear M 2 M′ 2 , 27,28 octanuclear M 4 M′ 4 , 29,30 pentanuclear M 3 M′ 2 , 31 and pentadecanuclear M 9 M′ 6 clusters. 32 −35 Among them, special attention is paid to trigonal-bipyramidal (TBP) M 3 M′ 2 clusters, realized by two axial polycyanidometallates forming bridges to three equatorial metal centers of octahedral geometry with four coordination sites blocked by chelating ligands.…”

“…32 −35 Among them, special attention is paid to trigonal-bipyramidal (TBP) M 3 M′ 2 clusters, realized by two axial polycyanidometallates forming bridges to three equatorial metal centers of octahedral geometry with four coordination sites blocked by chelating ligands. 31 The TBP clusters are usually obtained by the combination of [M III (CN) 6 ] 3− (M = Cr, Fe, Co, Mo, Os) ions and complexes of divalent 3d metal ions with diimine blocking ligands (e.g., tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline). 31,36 The few TBP molecules are built of tricyanidometallates, 37 39 The cyanido-bridged TBP-based crystalline solids exhibit a number of magnetic and optical functionalities, including both high-spin molecules, 40,41 single-molecule magnet (SMM) behavior, 37,42 thermal-induced and photoinduced SCO and CTIST phenomena, 43−45 and linkage isomerism.…”

An Unprecedented Charge Transfer Induced Spin Transition in an Fe–Os Cluster

“…These efforts led to the first documented case of CTIST 2 ] 2+ in acetonitrile leads to the formation of 1, which crystallizes in the centrosymmetric space group P2 1 /c as found for related TBP molecules (Figure 1). [16,17] The crystallographic data for 1 reveal that the average Fe À N(tmphen) bond length increases by 0.09-0.2 between 110 and 300 K, an indication that a change in the oxidation and/or spin states of these metal ions is occurring (Tables 1 and S1 in the Supporting Information). A large (ca.…”

“…[18] We have observed such a SCO transition for two of the three equatorial (2) site. This difference may be due to weak intra-and intermolecular interactions, [16] most likely related to the packing of the clusters into dimer units. In the dimers, there are p contacts between the tmphen ligands of Fe (1) [19,20] Therefore, the X-ray data indicate that the metal core in 1 is {(LS-Fe II ) 3 Figure 2).…”

Synthesis, structure and magnetic properties of two new coordination polymers with carboxylate-substituted benzoimidazole ligands

“…Recently, heterocyclic carboxylic acids were used as building blocks in constructing metal organic coordination polymers [4][5][6][7] . The investigation of magneto-structural correlations in coordination polymers has become a hot topic in the past decades [8][9][10][11][12] . The selection of bridging ligands is very important since it has a great effect on the magnetic properties of coordination polymers.…”