Wojciech Nitek

Double Switching of a Magnetic Coordination Framework through Intraskeletal Molecular Rearrangement

Molecular systems which undergo reversible structural transformations on application of external stimuli and show additional strongly intertwined physical phenomena are fundamental to the generation of nanoscale multifunctional molecular devices. Multifunctional molecular systems are recognized as potentially revolutionary magnetic, electric, and magneto-optical materials with possible applications in data storage/processing at the molecular level, as molecular switching devices in gas processing systems, and molecular sensors. In the field of porous molecular magnetic materials, the structural versatility of coordination chemistry has allowed the engineering of materials having novel topologies and remarkable properties. Magnetic coordination compounds with high magnetic ordering temperatures Tc exceeding the boiling point of liquid nitrogen are achievable in cyanidoor tetracyanoethylenebridged molecular solids. Incorporation of relatively large organic molecules into the structures of the former led to hybrid systems showing multifunctionality but usually with significantly lower Tc due to the lower ratio of bridging/ terminal CN ligands. Controlled dehydration of selected cyanido-bridged hybrids may result in substantial increase of Tc due to structural transformations involving terminal CN groups. However, there have been practically no reports on rational utilization of the terminal CN ligands and large organic molecules incorporated into the molecular framework to impart multifunctionality on these materials. Recently, we recognized the great potential of terminal CN groups and successfully exploited it in an Mn-imidazole– [Nb(CN)8] magnetic spongelike material to reversibly increase its critical temperature from 25 to 62 K. Here we present a cyanido-bridged molecular magnet in which the coordinated organic molecules and terminal CN ligands are appropriately arranged to provide a unique coexistence of molecule-specific porosity and doubly switchable high ordering temperature in one material. Orange platelike crystals of {[Mn(pydz)(H2O)2][Mn (H2O)2][Nb (CN)8]·2H2O}n (1; pydz = pyridazine, C4H4N2) were crystallized from an aqueous solution of MnCl2·4 H2O, pyridazine, and K4[Nb(CN)8]·2H2O (for details, see Supporting Information). Samples of 1 can be stored in a closed vessel for several months without decomposition. The structure of 1 was determined by single-crystal X-ray diffraction analysis (space group P21/c ; for details, see Supporting Information and CCDC 810685). The cyanido-bridged Mn2Nb skeleton of 1 (Figure 1a) consists of Mn2-NC-Nb square-grid motifs (in the bc plane) cross-linked at Nb centers by Mn1-NC-Nb ladders (along the a axis). Both Mn1 and Mn2 centers in 1 are octahedral (coordination number cn = 6), but their coordination spheres are different (Figure S2, top in the Supporting Information). Mn1 is coordinated by three nitrogen atoms of CN ligands (mer), one nitrogen atom of pyridazine (N11), and two aqua ligands in trans geometry. Mn1 belongs exclusively to the ladder motifs. The coordination sphere of Mn2, on the contrary, is purely inorganic and comprises four cyanido ligands in the equatorial plane and two aqua ligands in trans geometry. Mn2 belongs to the square-grid motifs. The only terminal CN ligand of the [Nb(CN)8] moiety (C4N4) is involved in a strong hydrogen bond with oxygen atom O11 of the aqua ligand coordinated to Mn1 (N4 Mn1 4.37 ). The noncoordinating nitrogen atom of the pyridazine ligand (N16) is involved in a hydrogen-bond to the aqua ligand (O22) of Mn2 (N16 Mn2 4.19 ; Figure 1a, bottom and Figure S3a in the Supporting Information). The local hydrogen-bonding system is completed by the H2O molecule of crystallization (O2) bound to O22 and N4. Such an arrangement is very promising from the point of view of topotactic reactivity of the terminal CN and pyridazine ligands. [*] Dr. D. Pinkowicz, Dr. R. Podgajny, Dr. B. Gaweł, Dr. W. Nitek, Prof. Dr. W. Łasocha, M. Oszajca, Prof. Dr. B. Sieklucka Faculty of Chemistry Jagiellonian University Ingardena 3, 30-060 Krak w (Poland) Fax: (+ 48)12-634-0515 E-mail: pinkowic@chemia.uj.edu.pl barbara.sieklucka@uj.edu.pl Homepage: http://www.chemia.uj.edu.pl/znmm/

Co–NC–W and Fe–NC–W Electron‐Transfer Channels for Thermal Bistability in Trimetallic {Fe6Co3[W(CN)8]6} Cyanido‐Bridged Cluster

The design and construction of switchable materials attracts tremendous interest owing to the potential in information storing and processing or molecular sensing. The archetypal examples involve a diversity of Fe-, 6] Feor Cobased spin-crossover (SCO) compounds, Co-catecholate/semiquinone systems, 11] as well as d-d bimetallic and sd-d trimetallic cyanide-bridged systems revealing chargetransfer-induced spin transitions (CTIST). Some of these compounds, for example Prussian blue analogues, are particularly promising from the point of view of photoswitching between nonmagnetic and magnetized (that is, TB, TC) states, owing to magnetic coupling through molecular bridges in discrete species 15] and extended networks. 18] Such bistability also emerged in the magnetochemistry of octacyanidometalates, exploiting metal-to-metal electron transfer in CoL[W(CN)8] 3 (L = pyrimidine, 4-methylpyridine) or canonical SCO in FeL[Nb(CN)8] 4 extended networks (L = 4-pyridinealdoxime). A magnetic hysteresis loop with a coercivity of 1–3 T were observed in an optically excited low-temperature metastable phase. As a continuing effort to obtain innovative bistable systems, we explored the simultaneous embedding of Co and Fe cations into one octacyanido-bridged coordination skeleton. We have engineered and isolated the novel trimetallic {Co3Fe II 6[W (CN)8]6(MeOH)24}·x MeOH (1) material built of nanosized (ca. 20 ) pentadecanuclear six-capped body-centered cubic Co3Fe6W6 clusters with MeOH molecules of crystallization (see the Supporting Information). The {M9M’ V 6(CN)48(L)24}·n solv compound family (M = Mn, Co, Ni; M’= Mo, W; L = blocking ligands; Figure 1) reveal high-

Nature of Magnetic Interactions in 3D {[MII(pyrazole)4]2[NbIV(CN)8]·4H2O}n (M = Mn, Fe, Co, Ni) Molecular Magnets

The self-assembly of [Nb(IV)(CN)(8)](4-) with different 3d metal centers in an aqueous solution and an excess of pyrazole resulted in the formation of four 3D isostructural compounds {[M(II)(pyrazole)(4)](2)[Nb(IV)(CN)(8)].4H(2)O}(n), where M(II) = Mn, Fe, Co, and Ni for 1-4, respectively. All four assemblies crystallize in the same I4(1)/a space group and show identical cyanido-bridged structures decorated with pyrazole molecules coordinated to M(II) centers. All four compounds show also long-range magnetic ordering below 24, 8, 6, and 13 K, respectively. A thorough analysis of the structural and magnetic data utilizing the molecular field model has allowed for an estimation of the values of coupling constants J(M-Nb) attributed to the one type of M(II)-NC-Nb(IV) linkage existing in 1-4. The J(M-Nb) values increase monotonically from -6.8 for 1 through -3.1 for 2 and +3.5 for 3, to +8.1 cm(-1) for 4 and are strongly correlated with the number of unpaired electrons on the M(II) metal center. Average orbital contributions to the total exchange coupling constants J(M-Nb) have also been identified and calculated: antiferromagnetic J(AF) = -21.6 cm(-1) originating from the d(xy), d(xz), and d(yz) orbitals of M(II) and ferromagnetic J(F) = +15.4 cm(-1) originating from d(z(2)) and d(x(2)-y(2)) orbitals of M(II). Antiferromagnetic interaction is successively weakened in the 1-4 row with each additional electron on the t(2g) level, which results in a change of the sign of J(M-Nb) and the nature of long-range magnetic ordering from ferrimagnetic in 1 and 2 to ferromagnetic in 3 and 4.

Natural and magnetic optical activity of 2-D chiral cyanido-bridged MnII–NbIV molecular ferrimagnets

Unique two dimensional enantiopure cyanido-bridged {[Mn(II)(R-mpm)2]2[Nb(IV)(CN)8]}·4H2O and {[Mn(II)(S-mpm)2]2[Nb(IV)(CN)8]}·4H2O (-S) (mpm = α-methyl-2-pyridine-methanol) ferrimagnets with TC = 23.5 K were synthesized and characterized. They reveal natural optical activity (NOA) due to the chiral crystal structure, and magnetic optical activity (MOA) in the presence of an external magnetic field, with the strong enhancement in the magnetically ordered phase below TC.

Spacer-dependent structural and physicochemical diversity in copper(II) complexes with salicyloyl hydrazones: a monomer and soluble polymers.

Complexation of copper(II) with a series of heterodonor chelating Schiff bases (LL) of salicylic acid hydrazide and aliphatic or cycloaliphatic ketones affords soluble one-dimensional (1D) metallopolymers containing Schiff bases as bridging ligands. Single-crystal X-ray diffraction results reveal nanometer-sized metallopolymeric wires [Cu(μ-LL)(2)](n) with off-axis linkers and a zigzag geometry. Octahedrally coordinated copper centers, exhibiting a Jahn-Teller distortion, are doubly bridged by two Schiff-base molecules in the μ(2)-η(1),η(2) coordination mode. The use of dibutylketone with long alkyl chains as a component for Schiff base formation leads to a distorted square planar monomeric copper(II) complex [Cu(LL)(2)], as evidenced by its X-ray crystal structure. The compounds are characterized by elemental analyses and IR and UV-vis spectroscopy, as well as magnetic susceptibility and cyclic voltammetry measurements. Electrochemical studies on the complexes reveal an existence of polymeric and monomeric forms in solution and the dependence of Cu(II)/Cu(I) reduction potentials on alkyl groups of salicyloyl hydrazone ligands. Polymeric complexes form conducting films on Pt electrodes upon multicycle potential sweeps.

W-Knotted Chain {[CuII(dien)]4[WV(CN)8]}5+∞: Synthesis, Crystal Structure, Magnetism, and Theory

The self-assembly of [Cu(II)(dien)(H(2)O)(2)](2+) and [W(V)(CN)(8)](3-) in aqueous solution leads to the formation (H(3)O){[Cu(II)(dien)](4)[W(V)(CN)(8)]}[W(V)(CN)(8)](2)·6.5H(2)O (1). The crystal structure of 1 consists of an unprecedented {[Cu(II)(dien)](4)[W(V)(CN)(8)]}(5+)(∞) chain of (2,8) topology, nonbridging [W(CN)(8)](3-) anions, and crystallization water molecules. The analysis of magnetic behavior of 1 was performed by the density functional theory (DFT) method and magnetic susceptibility measurements. The DFT broken symmetry approach gave two J(CuW) coupling constants: J(ax) = +2.9 cm(-1) assigned to long and strongly bent W-CN-Cu linkage, and the J(eq) = +1.5 cm(-1) assigned to short and less bent W-CN-Cu linkage, located at the axial and the equatorial positions of square pyramidal Cu(II) centers, respectively, in the hexanuclear {W(2)Cu(4)} chain subunit. The dominance of weak-to-moderate ferromagnetic coupling within the chain was confirmed by magnetic calculations. Zero-field susceptibility of the full chain segment {WCu(4)}(n) was calculated by a semiclassical analytical approach assuming that only one W(V) out of five ½ spins of the chain unit WCu(4) is treated as a classical commuting variable. The calculation of the field dependence of the magnetization was performed separately by replacing the same spin with the Ising variable and applying the standard transfer matrix technique. The intermolecular coupling between the chain segments and off-chain [W(CN)(8)](3-) entities was resolved using the mean-field approximation set to be of antiferromagnetic character. The magnetic coupling parameters are compared with those of other low dimensional {Cu(II)-[M(V)(CN)(8)]} systems.

Photo-induced magnetic properties of the [CuII(bapa)]2[MoIV(CN)8]·7H2O molecular ribbon

A unique one-dimensional ribbon [Cu(bapa)]2[Mo(CN)8]·7H2O (1) (bapa = bis(3-aminopropyl)amine), consisting of {[Cu(bapa)]3[Mo(CN)8]2}2− trigonal bipyramids and {[Cu(bapa)]2[Mo(CN)8]2}4− rhombuses linked through [Cu(bapa)]2+, was obtained and its photomagnetic properties were investigated. After irradiation at selected wavelengths (405 and 532 nm) or with white light, a global increase of the magnetic moment was observed. The initial state of the compound can be fully recovered by heating the sample above the temperature of relaxation of 253 K. This work was completed with photoreversibility studies with red and IR light irradiation which confirm a partial light-induced reversibility of the photomagnetic effect in 1. Finally, the photomagnetic phenomenon in 1 is discussed in accordance with two processes: the spin crossover on Mo(IV) centres and the metal-to-metal charge transfer mechanism in the Cu(II)–Mo(IV) pair.

Larger pores and higher Tc: {[Ni(cyclam)]3[W(CN)8]2·solv}n – a new member of the largest family of pseudo-polymorphic isomers among octacyanometallate-based assemblies

A new crystalline pseudo-polymorphic form of the 2D microporous honeycomb-like magnetic network {[Ni(cyclam)]3[W(CN)8]2·solv}n was obtained from the reaction between methanol-soluble {Ni[Ni(MeOH)3]8[W(CN)8]6} clusters and the [Ni(cyclam)]2+ complex in an acetonitrile-rich solvent mixture. In comparison to the three earlier characterised pseudo-polymorphs, which all crystallised in the triclinic space group P, the new form shows higher symmetry of C2/m, greater porosity of ca. 40% solvent accessible volume, and the highest magnetic ordering temperature of 12 K. It undergoes an irreversible single-crystal-to-single-crystal transformation to the hexadecahydrate form that is stable in air at ambient temperature. A new synthetic pathway leading directly to methanol solvate of the same network, which was previously obtained by sorption of MeOH into the anhydrous form, is also reported.

Microwave-assisted construction of ferromagnetic coordination polymers of [W(V)(CN)8]3- with Cu(II)-pyrazole synthons.

The microwave-mediated self-assembly of [W(V)(CN)(8)](3-) with Cu(II) in the presence of pyrazole ligand resulted in the formation of three novel assemblies: Cu(II)(2)(Hpyr)(5)(H(2)O)[W(V)(CN)(8)](NO(3))·H(2)O (1), {Cu(II)(5)(Hpyr)(18)[W(V)(CN)(8)](4)}·[Cu(II)(Hpyr)(4)(H(2)O)(2)]·9H(2)O (2), and Cu(II)(4)(Hpyr)(10)(H(2)O)[W(V)(CN)(8)](2)(HCOO)(2)·4.5H(2)O (3) (Hpyr =1H-pyrazole). Single-crystal X-ray structure of 1 consists of cyanido-bridged 1-D chains of vertex-sharing squares topology. The structure of 2 reveals 2-D hybrid inorganic layer topology with large coordination spaces occupied by {Cu(Hpyr)(2)(H(2)O)(4)}(2+) ions. Compound 3 contains two types of cyanido-bridged 1-D chains of vertex-sharing squares linked together by formate ions in two directions forming hybrid inorganic-organic 3-D framework (I(1)O(2)). The magnetic measurements for 1-3 reveal a weak ferromagnetic coupling through Cu(II)-NC-W(V) bridges.

MOLECULAR GEOMETRY, CYP1A GENE INDUCTION AND CLASTOGENIC ACTIVITY OF CYCLOPENTA[c]PHENANTHRENE IN RAINBOW TROUT

Cyclopenta[c]phenanthrene (CP[c]Ph) is a PAH member that shows similarities to bay-and fjord region possessing PAHs. On the basis of X-ray measurements it was found that the molecule of this hydrocarbon is planar. In this case, intramolecular strains caused by repulsion between protons in the pseudo fjord-region are balanced by both the shortening of some bonds which acquire more double bond character, and by the enlargement of exocyclic angles within the pseudo fjord-region. The activity of CP[c]Ph was investigated in vivo in rainbow trout, Oncorhynchus mykiss. The CYP1A mRNA levels following 48h-treatment with CP[c]Ph or benzo[a]pyrene (B[a]P; positive control) were determined and compared with incidences of clastogenic changes observed in the peripheral blood erythrocytes. We have found that the ability to induce CYP1A by these PAH compounds is positively correlated with the incidences of clastogenic changes in rainbow trout erythrocytes.