Photoswitchable CuMoIV and CuMoIV cyanido-bridged molecules

The self-assembly of copper(ii) complexes with two Schiff base ligands: L1_O = N₃ and L2 = N₄ and octacyanidomolybdate(iv) ions yields two discrete molecules of odd nuclearity, namely pentametallic [Cu(L1_O)(py)]₄[Mo^IV(CN)₈]·14H₂O (1), Cu₄Mo and trimetallic [Cu(L2)]₂[Mo^IV(CN)₈]·9H₂O (2), Cu₂Mo. Both molecular systems have been characterised structurally and magnetically, revealing a photomagnetic effect. In the case of (1) a metal-to-metal charge transfer (MMCT) mechanism is proposed. The analysis of magnetic interactions in the photogenerated state of (1) assumes the formation of the metastable cluster CuCu^IMo^V where metal centres in Mo^V-CN-Cu^II linkages are ferromagnetically coupled with J₂ = 104(3) cm^-1. In (2) the increase in the magnetisation is due to the singlet-triplet transition on the Mo^IV centre leading to the formation of the metastable CuMo. The presence of the paramagnetic Mo (S = 1) centre linking the Cu^II (S = 1/2) centres allows for effective ferromagnetic interaction of 3 paramagnetic centres with coupling constant J₂ = 20.2(7) cm^-1.

Phototunable magnetism in copper octacyanomolybdate

We introduce copper molybdenum cyanides of general formula Cu₂[Mo(CN)₈]·nH₂O, which can serve as optofunctional magnetic devices. Their ground states generally stay paramagnetic down to temperatures of the K order but exhibit a spontaneous magnetization upon photoirradiation usually below a few tens of K. To interest us still further, such a ferromagnetic stateinduced by blue-laser irradiation is demagnetized step by step through further application of red or near-infrared laser pulses. We solve this intriguing photomagnetism. The ground-state properties are fully revealed by means of a group-theoretical technique. Taking account of experimental observations, we simulate applying pump laser pulses to a likely ground state and successfully reproduce both the magnetization and demagnetization dynamics. We monitor the photorelaxation process through angle-resolved photoemission spectroscopy. Electrons are fully itinerant in any of the photoinduced steady states, forming a striking contrast to the initial equilibrium state of atomic aspect. The fully demagnetized final steady state looks completely different from the initial paramagnetism but bears good analogy to one of the possible ground states available with the Coulomb repulsion on Cu sites suppressed.

Chiral (LH)2L2Cu3 trinuclear paramagnetic nodes in octacyanidometalate-bridged helical chains

Trinuclear chiral (LH)2L2Cu3 (LH = 1,3-diamino-2-propanol, bdapH) assemblies linked by octacyanidometalate(IV) form isostructural one-dimensional (1D) chains consisting of right- and left-handed helixes arranged in an alternate manner: [(bdapH)2(bdap)2Cu(II)3][M(IV)(CN)8]·H2O (M = Mo 1, W 2). Each chain displays helicity with a long pitch around 17.2 Å. The direction of the helix rotation is strictly connected with the conformation of the (LH)2L2Cu3 unit. Right-handed helixes are based on Δ-S,S-(LH)2L2Cu3, whereas left-handed ones contain Λ-R,R-(LH)2L2Cu3 units. Magnetic studies reveal antiferromagnetic interactions through alkoxo-bridges inside trinuclear Cu(II) nodes leading to an ST = 1/2 ground state for both assemblies.

Design of one-dimensional coordination networks from a macrocyclic {3d-4f} single-molecule magnet precursor linked by [W(CN)8]3- anions

The outcome of 1:1 reactions of the tetranuclear 3d-4f Single Molecule Magnet (SMM) [Cu3Tb(L(Pr))(NO3)2(H2O)]NO3 (1) with (TBA)3[W(CN)8] (TBA = tri-n-butyl ammonium cation, [(n-Bu)3N-H](+)) in dimethylformamide (DMF) is dependent on the crystallization method employed: liquid-liquid diffusion of the reagents together gives {[Cu3Tb(L(Pr))W(CN)8(DMF)4]·(DMF)}n (2) whereas diethyl ether vapor diffusion into the reaction solution gives {[Cu3Tb(L(Pr))W(CN)8(DMF)3(H2O)3]·(DMF)1.5·(H2O)0.5}n (3). Both compounds are obtained as black single crystals and feature one-dimensional (1D) coordination networks (chains) of [1](3+) macrocycles linked by [W(CN)8](3-) anions. The two assemblies differ from a structural point of view. Complex 2 has a stepped arrangement with the linkers bound to the opposite faces of the macrocycle, whereas 3 has a square-wave arrangement due to the linkers binding to the same face of the macrocycle. Both compounds display an antiferromagnetic ground state below 3.5 and 2.4 K with a metamagnetic and antiferromagnetic (T, H) phase diagram for 2 and 3, respectively. Remarkably the slow dynamics of the magnetization of the [1](3+) macrocycle units is preserved in 3 while this property is quenched in 2 because of stronger intra- and interchain magnetic interactions inducing a higher critical temperature.

Variation of Heterometallic Structural Motifs Based on [W(CN)8]3− Anions and MnII Ions as a Function of Synthetic Conditions

Reactions of [W(CN)(8)](3-/4-) anions with complexes of Mn(2+) ion with tridentate organic ligand 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) lead to a series of heterobimetallic complexes. The crystal structures of these compounds are derived from the same basic structural fragment, namely a W(2)Mn(2) square constructed of alternating cyanide-bridged W and Mn ions. In [Mn(II)(tptz)(OAc)(H(2)O)(2)](2){[Mn(II)(tptz)(MeOH)(1.58)(H(2)O)(0.42)](2)[W(V)(CN)(8)](2)}.5 MeOH.9.85 H(2)O (3), isolated molecular squares are co-crystallized with mononuclear cationic Mn(II) complexes. The structure of {[Mn(II)(tptz)(MeOH)](2)[W(IV)(CN)(8)].2 MeOH}(infinity) (4) is based on an infinite chain of vertex-sharing squares, while {[Mn(II) (2)(tptz)(2)(MeOH)(3)(OAc)][W(V)(CN)(8)].3.5 MeOH0.25 H(2)O}(infinity) (5) and {[Mn(II) (2)(tptz)(2)(MeOH)(3)W(V)(CN)(8)][Mn(II)(tptz)(MeOH)W(V)(CN)(8)].2 H(2).OMeOH}(8) (7) are derived from such an infinite chain by removing one of the W-C[triple bond]N-Mn linkages in each of the squares. The decanuclear cluster [Mn(II) (6)(tptz)(6)(MeOH)(4)(DMF)(2)W(V) (4)(CN)(32)].8.2 H(2)O.2.3 MeOH (6) is a truncated version of structure 4 and consists of three vertex-sharing W(2)Mn(2) squares. The structure of [Mn(II)(tptz)(MeOH)(NO(3))](2)[Mn(II)(tptz)(MeOH) (DMF)](2)[W(V)(CN)(8)](2).6 MeOH (8) consists of a hexanuclear cluster, in which the central W(2)Mn(2) square is extended by two Mn side-arms attached via CN(-) ligands to the W corners of the square. The magnetic behavior of these heterobimetallic complexes (except for 4) is dominated by antiferromagnetic coupling between Mn(II) and W(V) ions mediated by cyanide bridges. Compounds 3, 6, and 8 exhibit high spin ground states of S=4, 13, and 9, respectively, while 5 and 7 exhibit behavior typical of a ferrimagnetic chain with alternating spin centers. Complex 4 contains diamagnetic W(IV) centers but holds promise as a potential photomagnetic solid.

Two WV–MnIIIbimetallic assemblies built by octacyanotungstate(v) and MnIIISchiff bases: molecular structures and a spin-flop transition

Two W(V)-Mn(III) bimetallic compounds, [Mn(Cl-salmen)(H(2)O)2]{[Mn(5-Clsalmen)(H(2)O)]2[W(CN)8].2H(2)O (1.2H(2)O) [5-Clsalmen = N,N'-(1-methylethylene)bis(5-chlorosalicylideneiminato) dianion], which contains trinuclear Mn(2)W and isolated Mn(III) moieties, and [Mn(3-MeOsalcy)(H(2)O)2]3[W(CN)(8)].2H(2)O (2.2H(2)O) [3-MeOsalcy = N,N'-(trans-1,2-cyclohexanediylethylene)bis(3-methoxysalicylideneiminato) dianion] molecules were prepared in redox processes and characterized using X-ray analysis and magnetic measurements. Compound 1 is composed of the {[Mn(5-Clsalmen)(H(2)O)]2[W(CN)8]}- trimer, in which two CN groups among eight in [W(CN)8](3-) bridge W(5+) and two Mn(3+) ions and the remaining CN ligands are hydrogen-bonded to water molecules or unbound, and the [Mn(Cl-salmen)(H(2)O)2]+ cation. Subsequently, two water molecules of the isolated cation are subject to hydrogen bonds. For 2, there are no covalent bonds among the subunits and six serial stacks of [Mn(3-MeOsalcy)(H(2)O)2]+ units are all hydrogen-bonded. The many hydrogen bonds found in both complexes eventually lead to three-dimensional networks. The magnetic studies for 1 reveal that antiferromagnetic interactions (J = -5.4 cm(-1)) between W(V) and Mn(III) centers within the trimer are transmitted via the bridging CN groups. Intermolecular antiferromagnetic couplings (zJ' = -0.2 cm(-1)) are also observed. The static and dynamic magnetic data of 1 demonstrate the existence of a field-induced spin-flop transition occurring among the clusters and monomeric molecules.

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

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.

Cobalt(ii) octacyanotungstate(v) organic–inorganic hybrid ferromagnetic materials with pyrazine and 4,4′-bipyridine

Two new ferromagnetic organic-inorganic hybrid materials [Co(II)3(H2O)6(pyz)3[W(V)(CN)8]2].3.5H2O (1) and [Co(II)3(H2O)4(4,4'-bpy)3[W(V)(CN)8]2].1.5(4,4'-bpy).6H2O (2) have been synthesised and characterised. The structure of the compounds have been investigated combining EXAFS (extended X-ray absorption fine structure), ES-MS (electrospray mass spectrometry), IR (infrared spectroscopy), UV-VIS electronic spectroscopy and TGA (thermogravimetric analysis) coupled with QMS (quadrupole mass spectrometer) experiments. The studies reveal that both compounds consist of Co(II)-NC-W(V) and Co(II)-L-Co(II) linkages (L = pyrazine (1) or 4,4-bipyridine (2)). Both networks are created by cyano-bridged Co(II)3W(V)2 chains joined by organic linkers into a 2D architecture. A difference of cobalt coordination numbers in both compounds derived from EXAFS study is consistent with the ES-MS conclusion. The ac magnetic characterisation exhibits the transition to the ferromagnetic phase at T(C) = 26 K (1) and to the spin glass-like phase at T(G) = 16 K (2). The frequency dependent chi'(T) and chi''(T) signals indicate the presence of some disorder in spin alignment below ordering temperatures. Both networks are also characterised a by magnetic hysteresis loop of coercive field H(c) = 750 Oe (1) and 1200 Oe (2) at T = 4.2 K.

Electrochemical Synthesis, Crystal Structure, and Photomagnetic Properties of a Three-Dimensional Cyano-Bridged Copper−Molybdenum Complex

A single crystal of Cs(I)2Cu(II)7[Mo(IV)CN8]4.6H2O was electrochemically prepared on a Pt wire electrode with a constant potential of +500 mV vs Ag/AgCl electrode. X-ray single-crystal structural analysis showed that this compound consists of a three-dimensional cyano-bridged Cu-Mo bimetallic assembly with a tetragonal structure of I4/mmm. The coordination geometry of Mo(IV) is bicapped trigonal prism, and that of Cu(II) is five-coordinate of square pyramidal or four-coordinate of square planar. This compound was also prepared as a 0.2-3.0 microm thick film on a SnO2-coated glass in the same electrochemical manner. When the sample, which shows paramagnetism due to Cu(II) (S = 1/2), was irradiated with 450-500 nm light at 5 K, spontaneous magnetization with a Curie temperature of 23 K was observed. This photoinduced change was recovered by a thermal treatment. In the infrared (IR) and electron spin resonance (ESR) spectra after light irradiation, variations in the stretching IR peak of CN bridged to Mo(IV) and the paramagnetic ESR peak of Cu(II) were observed, respectively. The data indicate that this photomagnetism is caused by the electron transfer from Mo(IV) to Cu(II) and the ferromagnetic ordering between Cu(II) (S = 1/2) and Mo(V) (S = 1/2).

An unprecedented copper(i,ii)–octacyanotungstate(v) 2-D network: crystal structure and magnetism of [CuII(tren)]{CuI[WV(CN)8]}·1.5H2O

A novel two-dimensional cyanide-bridged polymer [CuII(tren)]{CuI[W(V)(CN)8]} . 1.5H2O (tren = tris(2-aminoethyl)amine) formed via the simultaneous in situ metal-ligand redox reaction of [Cu(tren)(OH2)]2+ and self-assembly with [W(V)(CN)8]3- consists of a {CuI[W(V)(CN)8]} square grid built of CuI centres of tetrahedral geometry coordinatively saturated by CN bridges and [W(V)(CN)8]3- capped by [CuII(tren)]2+ moieties; it exhibits ferromagnetic coupling J1 = +5.8(1) cm(-1) within the CuII-W(V) dinuclear subunits and weak antiferromagnetic coupling J2 = -0.03(1) cm(-1) between them through diamagnetic CuI spacers.

Cyano-bridged gadolinium(iii)-tungstate(v) bimetallic assembly with a one-dimensional chain structure

In this paper, we report the crystal structure and magnetic properties of the cyano-bridged gadolinium-tungstate bimetallic assembly, GdIII(DMF)6[WV(CN)8](DMF =N,N-dimethylformamide). X-Ray single crystal analysis shows that this compound crystallizes in the monoclinic system of space group P2(1)/c with cell constants a= 16.40(2)A, b= 11.08(1)A, c= 21.18(2)A, beta= 91.09(8) degrees, and Z= 4. The crystal consists of one-dimensional linear chains, in which [GdIII(DMF)6]3+ and [WV(CN)8]3- ions are linked in an alternating fashion. The magnetic data show that this compound is a paramagnet with an antiferromagnetic coupling of -0.58 cm-1 between GdIII(S= 7/2) and WV(S= 1/2).

Crystal Structures and Magnetic Properties of Two Low-Dimensional Materials Constructed from [MnIII(salen)H2O]+ and [M(CN)8]3-/4- (M = Mo or W) Precursors

The syntheses, X-ray structures, and magnetic behaviors of two new cyano-bridged assemblies, the molecular [Mn(III)(salen)H2O]3[W(V)(CN)8].H2O (1) and one-dimensional [Mn(salen)(H2O)2]2[[Mn(salen)(H2O)][Mn(salen)]2[Mo(CN)(8)]].0.5ClO4.0.5OH.4.5H2O (2), are presented. Compound 1 crystallizes in the monoclinic system, has space group P2(1)/c, and has unit cell constants a = 13.7210(2) A, b = 20.6840(4) A, c = 20.6370(2) A, and Z = 4. Compound 2 crystallizes in the triclinic system, has space group P, and has unit cell dimensions a = 18.428(4) A, b = 18.521(3) A, c = 18.567(4) A, and Z = 2. The structure of 1 consists of the asymmetric V-shaped Mn-NC-W-NC-Mn-O(phenolate)-Mn molecules, where W(V) coordinates with [Mn(salen)H2O] and singly phenolate-bridged [Mn(salen)H2O]2 moieties through the neighboring cyano bridges. The [W(V)(CN)8]3- ion displays distorted square-antiprism geometry. The structure of 2 consists of the cyano-bridged [Mn3(III)Mo(IV)]n- repeating units linked by double phenolate bridges into one-dimensional zigzag chains. The Mn(III) centers are bound to Mo(IV) of square-antiprism geometry through the neighboring cyano bridges. The magnetic studies of 1 reveal the antiferromagnetic intramolecular interactions through the CN and phenolate bridges and the relatively weak intermolecular interactions. Compound 1 becomes antiferromagnetically ordered below TN = 4.6 K. The presence of the magnetic anisotropy is documented with the MH measurements carried out for both polycrystalline and single-crystal samples. At T = 1.9 K, the spin-flop transition is observed in the field of 18 kOe applied parallel to the bc plane, which is the easy plane of magnetization. Field dependence of magnetization of 1 shows field-induced metamagnetic behavior from the antiferromagnetic ground state of ST = 3/2 to the state of ST = 5/2. The magnetic properties of 2 indicate a weak antiferromagnetic interaction between Mn(III) centers in double-phenolate-bridged [Mn(III)(salen)]2 dinuclear subunits and a very weak ferromagnetic interaction between them through the diamagnetic [Mo(IV)(CN)8]4- spacer.