Temperature and light induced bistability in a Co3[Os(CN)6]2 6 H2O Prussian blue analog.

To expand the field of new cyanide materials of the 5d elements, we incorporated the [Os(CN)(6)](3-) anion into PB architectures in combination with the Co(II) cation. Herein, we report the first example of a photomagnetic PB analog containing Os(III) ions. In a similar vein as the prototypical CoFe PB analogs, this compound exhibits a wide variety of properties including Charge Transfer Induced Spin Transition (CTIST), Temperature Induced Excited Spin State Trapping (TIESST), and magnetic ordering.

Cyanide lability and linkage isomerism of hexacyanochromate(III) induced by the Co(II) ion.

Reactions between the [M(III)(CN)(6)](3-) (M = Fe and Co) anions and the mononuclear complex [Co(II)(dppe)(2)(H(2)O)][BF(4)](2) result in the formation of two isostructural trinuclear clusters {[Co(II)(dppe)(2)](2)[M(III)(CN)(6)]}(BF(4)). Surprisingly, reactions of [Co(dppe)(2)(H(2)O)](BF(4))(2) and [Co(triphos)(CH(3)CN)(2)](BF(4))(2) with [Cr(CN)(6)](3-) yield the mononuclear complexes [Co(dppe)(2)(CN)](BF(4)) and [Co(triphos)(CN)(2)], respectively. In the former case, an unusual pentanuclear intermediate complex {[Co(II)(3)(dppe)(4)(MeCN)][Cr(III)(CN)(6)](2)} was isolated. The reaction was probed by solution IR spectroscopy, which revealed a gradual conversion of the nu(C[triple bond]N) stretches of the starting materials to those of the CN-bridged intermediate and eventually to the single nu(C[triple bond]N) stretch of the final mononuclear product. The loss of carbon-bound CN(-) ligands from [Cr(CN)(6)](3-) occurs on a sufficiently slow time-scale for observation of varying degrees of cyanide linkage isomerism in the trigonal bipyramidal complex {[Co(tmphen)(2)](3)[Cr(CN)(6)](2)}; the study was aided by the use of different Co(II) starting materials. Results obtained by a combination of X-ray crystallography, infrared spectroscopy, and magnetometry provide unequivocal evidence that the presence of certain Lewis acids (e.g., Co(II) in this work and Fe(II) ions and BPh(3) in previously reported studies) promote the process of cyanide linkage isomerism, which, in the case of Co(II) species, leads to facile labilization of cyanide ligands from the [Cr(CN)(6)](3-) anion.

Trigonal-bipyramidal metal cyanide complexes: a versatile platform for the systematic assessment of the magnetic properties of Prussian blue materials.

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.

Highly anisotropic exchange interactions in a trigonal bipyramidal cyanide-bridged Ni(II)3Os(III)2 cluster.

This article is a part of our efforts to control the magnetic anisotropy in cyanide-based exchange-coupled systems with the eventual goal to obtain single-molecule magnets with higher blocking temperatures. We give the theoretical interpretation of the magnetic properties of the new pentanuclear complex {[Ni(II)(tmphen)(2)](3)[Os(III)(CN)(6)](2)} x 6 CH(3)CN (Ni(II)(3)Os(III)(2) cluster). Because the system contains the heavy Os(III) ions, spin-orbit coupling considerably exceeds the contributions from the low-symmetry crystal field and exchange coupling. The magnetic properties of the Ni(II)(3)Os(III)(2) cluster are described in the framework of a highly anisotropic pseudo-spin Hamiltonian that corresponds to the limit of strong spin-orbital coupling and takes into account the complex molecular structure. The model provides a good fit to the experimental data and allows the conclusion that the trigonal axis of the bipyramidal Ni(II)(3)Os(III)(2) cluster is a hard axis of magnetization. This explains the fact that in contrast with the isostructural trigonal bipyramidal Mn(III)(2)Mn(II)(3) cluster, the Ni(II)(3)Os(III)(2) system does not exhibit the single-molecule magnetic behavior.

Trigonal bipyramidal magnetic molecules based on [Mo(III)(CN)(6)](3-).

The trigonal bipyramidal molecules [M(tmphen)(2)](3)[Mo(CN)(6)](2).(solvent) (M = Co, Ni; tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline) based on the [Mo(III)(CN)(6)](3-) unit were prepared by loss of a cyanide ligand from [Mo(III)(CN)(7)](4-) and found to exhibit ferromagnetic interactions between the M(II) and Mo(III) centers.

Use of a rhenium cyanide nanomagnet as a building block for new clusters and extended networks.

Derivatives of the single molecule magnet (SMM) {[Re(triphos)(CN)(3)](4)[MnCl](4)} (Re(4)Mn(4)) {[Re(triphos)(CN)(3)](4)[Mn(CH(3)CN)](4)}(ClO(4))(4) (2) and {[Re(triphos)(CN)(3)](4)[Mn(ClO(4))](3)[Mn(CH(3)OH)(CH(3)O)]} (3), were prepared by reacting [Et(4)N][Re(triphos)(CN)(3)] (1) with Mn(ClO(4))(2)·6H(2)O. Reaction of sodium dicyanamide, NaN(CN)(2), with compound 2 in CH(2)Cl(2) results in the product {[Re(triphos)(CN)(3)](4)[Mn(N(CN)(2))](4)} (4), in which each Mn(II) site is terminated by a dicyanamide ligand. A similar reaction of compound 3 in CH(2)Cl(2)-MeOH solution with LiTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) leads to the formation of {[Re(triphos)(CN)(3)](4)[Mn(TCNQ-TCNQ)(3)(Mn(HTCNQ)(CH(3)O))]} (5) whose structure is best described as a chain of dimers of Re(4)Mn(4) cubes bridged by sigma-bonded (TCNQ(2))(2-) linkers with one capping HTCNQ ligand.

Molecules based on M(v) (M=Mo, W) and Ni(II) ions: a new class of trigonal bipyramidal cluster and confirmation of SMM behavior for the pentadecanuclear molecule {NiII[NiII(tmphen)(MeOH)]6[Ni(H2O)3]2[micro-CN]30[WV(CN)3]6}.

The preparation, single crystal X-ray crystallography, and magnetic properties are reported for four new clusters based on [M'V(CN)8]3- octacyanometallates (M'=Mo, W). Reactions of [M'V(CN)8]3- with mononuclear NiII ions in the presence of the tmphen blocking ligand (tmphen=3,4,7,8-tetramethyl-1,10-phenanthroline) in a 2:3:6 ratio, respectively, lead to the formation of the trigonal bipyramidal clusters [NiII(tmphen)2]3[M'V(CN)8]2. Analogous reactions with the same starting materials performed in a 2:3:2 ratio, respectively, produce pentadecanuclear clusters of the type {NiII[NiII(tmphen)(MeOH)]6[Ni(H2O)3]2[micro-CN]30[WV(CN)3]6}. The W2Ni3 (1) and Mo2Ni3(2) pentanuclear clusters and the W6Ni9 (3) and Mo6Ni9 (4) pentadecanuclear molecules are isostructural to each other and crystallize in the space groups P2(1)/c and R3 respectively. Magnetic measurements indicate that the ground states for the trigonal bipyamidal clusters are S=4 as a consequence of ferromagnetic coupling with JW-Ni=9.5 cm(-1), JMo-Ni=10 cm(-1). The pentadecanuclear clusters exhibit ferromagnetic coupling as well, which leads to S=12 ground states (JW-Ni=12 cm(-1), JMo-Ni=12.2 cm(-1)). Reduced magnetization studies on the W-Ni analogues support the conclusion that they exhibit a negative axial anisotropy term; the fits give D values of -0.24 cm(-1) for the W2Ni3 cluster and D=-0.04 cm(-1)for the W6Ni9 cluster. AC susceptibility measurements indicate the beginning of an out-of-phase signal for the W2Ni3 and the W6Ni9 compounds, but detailed low temperature studies on small crystals by the microSQUID technique indicate that only the pentadecanuclear cluster exhibits hysteresis in accord with SMM behavior. Neither Mo cluster reveals any evidence for slow paramagnetic relaxation at low temperatures.

Hexacyanoosmate(III) chemistry: preparation and magnetic properties of a pentanuclear cluster and a Prussian blue analogue with Ni(II).

The hexacyanoosmate(III) anion was used to prepare a pentanuclear cyanide bridged molecular cluster with ligand-protected Ni(II) ions as well as the corresponding Prussian blue phase from a reaction with aqueous Ni(II) ions.

Photocytotoxicity of a new Rh2(II,II) complex: increase in cytotoxicity upon irradiation similar to that of PDT agent hematoporphyrin.

A new type of heteroleptic dirhodium complex cis-[Rh(2)(mu-O2CCH3)2-(bpy)(dppz)]2+ (3) was synthesized and its potential as a photodynamic therapy (PDT) agent was investigated. Although 27% hypochromicity of the absorption of 3 in the near-UV and visible regions is observed in the presence of duplex DNA, relative viscosity measurements reveal that the complex does not intercalate between the DNA bases. The DNA photocleavage with visible light by 3 proceeds via both oxygen dependent and independent mechanisms, and it is more efficient than that of related complexes. The increase in the cytotoxicity of 3 towards human skin cells is similar to that of hematoporphyrin, a key ingredient in a PDT drug currently in use. This feature makes this complex a useful candidate for further PDT studies.