A photochromic trinuclear dysprosium(iii) single-molecule magnet with two distinct relaxation processes

Multifunctional molecules responsive to light are highly desired as components for the construction of remotely controlled nanodevices. Here we present a DyIII single molecule magnet (SMM) comprising dithienylethene (dte) photochromic bridging ligands in the form of a pyridine (py) derivative: 1,2-bis((2-methyl-5-pyridyl)thie-3-yl)perfluorocyclo-pentene (dtepy). The title trinuclear compound {[DyIII(BHT)3]3(dtepy)2}·4C5H12 (1) was synthesized by combining the low-coordinate dysprosium complexes DyIII(BHT)3 (BHT = 2,6-di-tert-butyl-4-methylphenolate) with dtepy bridging ligands in the 'open' form using n-pentane as a completely inert solvent. The trinuclear molecule comprises two different DyIII centers due to its quasi-linear geometry: a central trigonal bipyramidal DyIII ion and two peripheral ones with an approximate trigonal pyramidal geometry. Thanks to that, 1 shows two types of SMM behavior which is slightly affected by the photoisomerization of the photochromic dtepy bridges. The impact of the photoisomerization on the magnetization dynamics was studied by means of alternating current (AC) magnetic susceptibility measurements for the 'open' and 'closed' forms of the molecules. The changes between the 'open' and 'closed' isomers were further investigated by IR and UV-vis spectroscopy, suggesting the co-existence of the ligand-related photochromism and single-molecule magnet behavior in 1. However, the powder X-ray diffraction studies indicate loss of structural order in the first photoisomerization step preventing in-depth studies.

Guest-induced pore breathing controls the spin state in a cyanido-bridged framework

Iron(ii) spin cross-over (SCO) compounds combine a thermally driven transition from the diamagnetic low-spin (LS) state to the paramagnetic high-spin (HS) state with a distinct change in the crystal lattice volume. Inversely, if the crystal lattice volume was modulated post-synthetically, the spin state of the compound could be tunable, resulting in the inverse effect for SCO. Herein, we demonstrate such a spin-state tuning in a breathing cyanido-bridged porous coordination polymer (PCP), where the volume change resulting from guest-induced gate-opening and -closing directly affects its spin state. We report the synthesis of a three-dimensional coordination framework {[FeII(4-CNpy)4]2[WIV(CN)8]·4H2O}n (1·4H2O; 4-CNpy = 4-cyanopyridine), which demonstrates a SCO phenomenon characterized by strong elastic frustration. This leads to a 48 K wide hysteresis loop above 140 K, but below this temperature results in a very gradual and incomplete SCO transition. 1·4H2O was activated under mild conditions, producing the nonporous {[FeII(4-CNpy)4]2[WIV(CN)8]}n (1) via a single-crystal-to-single-crystal process involving a 7.3% volume decrease, which shows complete and nonhysteretic SCO at T1/2 = 93 K. The low-temperature photoswitching behavior in 1 and 1·4H2O manifested the characteristic elasticity of the frameworks; 1 can be quantitatively converted into a metastable HS state after 638 nm light irradiation, while the photoactivation of 1·4H2O is only partial. Furthermore, nonporous 1 adsorbed CO2 molecules in a gated process, leading to {[FeII(4-CNpy)4]2[WIV(CN)8]·4CO2}n (1·4CO2), which resulted in a 15% volume increase and stabilization of the HS state in the whole temperature range down to 2 K. The demonstrated post-synthetic guest-exchange employing common gases is an efficient approach for tuning the spin state in breathing SCO-PCPs.

Approaching the free-ion limit in magnetically isotropic gadolinium(III) via borohydride ligands

Three new crystalline phases of the borohydride complex, [n-Bu4N][RE(BH4)4] (RE = Gd (1), Gd0.097Y0.903 (2) and Gd0.017Y0.983 (3)), were obtained in pure form and characterised using EPR spectroscopy and AC/DC...

Magnetic interactions controlled by light in the family of Fe(II)-M(IV) (M = Mo, W, Nb) hybrid organic-inorganic frameworks

Three new hybrid organic-inorganic frameworks employing octacyanidometallates and 4,4'-bypiridine dioxide (4,4'-bpdo) as bridging molecules were prepared and characterized. The three-dimensional coordination frameworks {[Fe^II(μ-4,4'-bpdo)(H₂O)₂]₂[M^IV(CN)₈]·9H₂O}_n (Fe2Mo, Fe2W and Fe2Nb; M = Mo, W and Nb) are composed of cyanido-bridged chains, which are interconnected by the organic linkers. Magnetic measurements for Fe2Nb show a two-step transition to the antiferromagnetic state, which results from the cooperation of antiferromagnetic intra- and inter-chain interactions. Fe2Mo and Fe2W, on the other hand, behave as paramagnets at 2 K because of the diamagnetic character of the corresponding octacyanidometallate(IV) building units. However, after 450 nm light irradiation they show transition to the metastable high spin Mo^IV or W^IV states, respectively, with distinct ferromagnetic intrachain spin interactions, as opposed to the antiferromagnetic ones observed in the Fe2Nb framework.

Antagonist elastic interactions tuning spin crossover and LIESST behaviours in FeII trinuclear-based one-dimensional chains

A new 1-D spin SCO coordination polymer based on FeII trinuclear units covalently linked by a flexible coligand has been reported as an unusual platform and model system for experimental study on the origin of the step-like feature in 1-D systems.

Chiral porous CN-bridged coordination polymer mimicking MOF-74 and showing magnetization photoswitching

A chiral porous cyanide-bridged framework {[Mn^II(L)]₂[W^IV(CN)₈]·10H₂O}_n (1; L = 2,6-bis[1-(2-(N-methylamino)ethylimino)ethyl]-pyridine) showing a strong structural similarity to MOF-74 has been prepared and characterised. The crystallised water molecules can be easily removed below 60 °C, leading to a distinct crystal colour change and the activation of its photomagnetic properties - constituting the so called photomagnetic sponge behaviour of this system. The complete dehydration of 1 proceeds through a single-crystal-to-single-crystal transformation and the resulting anhydrous framework {[Mn^II(L)]₂[W^IV(CN)₈]}_n (1anh) was studied using single-crystal X-ray diffraction.

Large breathing effect induced by water sorption in a remarkably stable nonporous cyanide-bridged coordination polymer

While metal-organic frameworks (MOFs) are at the forefront of cutting-edge porous materials, extraordinary sorption properties can also be observed in Prussian Blue Analogs (PBAs) and related materials comprising extremely short bridging ligands. Herein, we present a bimetallic nonporous cyanide-bridged coordination polymer (CP) {[Mn(imH)]2[Mo(CN)8]} n (1Mn; imH = imidazole) that can efficiently and reversibly capture and release water molecules over tens of cycles without any fatigue despite being based on one of the shortest bridging ligands known - the cyanide. The sorption performance of {[Mn(imH)]2[Mo(CN)8]} n matches or even outperforms MOFs that are typically selected for water harvesting applications with perfect sorption reversibility and very low desorption temperatures. Water sorption in 1Mn is possible due to the breathing effect (accompanied by a dramatic cyanide-framework transformation) occurring in three well-defined steps between four different crystal phases studied structurally by X-ray diffraction structural analysis. Moreover, the capture of H2O by 1Mn switches the EPR signal intensity of the MnII centres, which has been demonstrated by in situ EPR measurements and enables monitoring of the hydration level of 1Mn by EPR. The sorption of water in 1Mn controls also its photomagnetic behavior at the cryogenic regime, thanks to the presence of the [MoIV(CN)8]4- photomagnetic chromophore in the structure. These observations demonstrate the extraordinary sorption potential of cyanide-bridged CPs and the possibility to merge it with the unique physical properties of this class of compounds arising from their bimetallic character (e.g. photomagnetism and long-range magnetic ordering).

Octacyanidometallates for multifunctional molecule-based materials

Octacyanidometallates have been successfully employed in the design of heterometallic coordination systems offering a spectacular range of desired physical properties with great potential for technological applications. The [M(CN)8]n- ions comprise a series of complexes of heavy transition metals in high oxidation states, including NbIV, MoIV/V, WIV/V, and ReV. Since the discovery of the pioneering bimetallic {MnII4[MIV(CN)8]2} and {MnII9[MV(CN)8]6} (M = Mo, W) molecules in 2000, octacyanidometallates were fruitfully explored as precursors for the construction of diverse d-d or d-f coordination clusters and frameworks which could be obtained in the crystalline form under mild synthetic conditions. The primary interest in [M(CN)8]n--based networks was focused on their application as molecule-based magnets exhibiting long-range magnetic ordering resulting from the efficient intermetallic exchange coupling mediated by cyanido bridges. However, in the last few years, octacyanidometallate-based materials proved to offer varied and remarkable functionalities, becoming efficient building blocks for the construction of molecular nanomagnets, magnetic coolers, spin transition materials, photomagnets, solvato-magnetic materials, including molecular magnetic sponges, luminescent magnets, chiral magnets and photomagnets, SHG-active magnetic materials, pyro- and ferroelectrics, ionic conductors as well as electrochemical containers. Some of these materials can be processed into the nanoscale opening the route towards the development of magnetic, optical and electronic devices. In this review, we summarise all important achievements in the field of octacyanidometallate-based functional materials, with the particular attention to the most recent advances, and present a thorough discussion on non-trivial structural and electronic features of [M(CN)8]n- ions, which are purposefully explored to introduce desired physical properties and their combinations towards advanced multifunctional materials.

Heterotrimetallic Cyanide-Bridged 3d-4d-5d Frameworks Based on a Photomagnetic Secondary Building Unit

The rational design of coordination frameworks combining more than two different metal ions using a self-assembly approach is challenging because it rarely offers sufficient control over the building blocks at the actual self-assembly stage. In this work, we present a successful two-step strategy toward heterotrimetallic coordination frameworks by employing a new bimetallic [(NC)₇Mo^IV-CN-Pt^IV(NH₃)₄-NC-Mo^IV(CN)₇]^4– secondary building unit (SBU). This anionic moiety has been isolated and characterized as a simple salt with an organic dppipH₂²⁺ cation (dppipH₂)₂[(NC)₇Mo^IV-CN-Pt^IV(NH₃)₄-NC-Mo^IV(CN)₇]·15H₂O (1) (dppip = 1,4-di(4-pyridinyl)piperazine). The salt presents a second-order phase transition related to cation conformational change around 250 K and a photomagnetic effect after irradiation with 450 nm light at 10 K. When combined with aqueous solutions of Mn^II or Cu^II complexes, it forms either a one-dimensional chain [Mn^II(dpop)][Mn^II(dpop)(H₂O)][(NC)₇Mo^IV-CN-Pt^IV(NH₃)₄-NC-Mo^IV(CN)₇]·36H₂O (2) (dpop = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene) or a photomagnetic two-dimensional honeycomb network [Cu^II(cyclam)]₂[(NC)₇Mo^IV-CN-Pt^IV(NH₃)₄-NC-Mo^IV(CN)₇]·40.89H₂O (3) (cyclam = 1,4,8,11-tetraazacyclotetradecane), both characterized by very large cavities in their structure filled with solvent molecules. Both 2 and 3 incorporate three different transition-metal ions and constitute a new family of 3d-4d-5d coordination frameworks. Moreover, compound 3 inherits the photomagnetic properties of the MoPtMo SBU.

A photomagnetic secondary building unit (SBU) Mo^IVPt^IVMo^IV was employed to design and synthesize new heterotrimetallic coordination polymers in a two-step approach, resulting in Mn^II₂Mo^IV₂Pt^IV coordination chains and Cu^II₂Mo^IV₂Pt^IV honeycomb coordination layers.

Magnetization Dynamics and Coherent Spin Manipulation of a Propeller Gd(III) Complex with the Smallest Helicene Ligand

A homoleptic gadolinium(III) complex with the smallest helicene-type ligand, 1,10-phenanthroline-N,N'-dioxide (phendo) [Gd(phendo)₄](NO₃)₃·xMeOH (phendo = 1,10-phenanthroline-N,N'-dioxide, MeOH = methanol), shows slow relaxation of the magnetization characteristic for Single Ion Magnets (SIM), despite negligible magnetic anisotropy, confirmed by ab initio calculations. Solid state dilution magnetic and EPR studies reveal that the magnetization dynamics of the [Gd(phendo)₄]³⁺ cation is controlled mainly by a Raman process. Pulsed EPR experiments demonstrate long phase memory times (up to 2.7 μs at 5 K), enabling the detection of Rabi oscillations at 20 K, which confirms coherent control of its spin state.

Photoinduced Mo-CN Bond Breakage in Octacyanomolybdate Leading to Spin Triplet Trapping

The photoinduced properties of the octacoordinated complex K₄ Mo^IV (CN)₈ ⋅2 H₂ O were studied by theoretical calculations, crystallography, and optical and magnetic measurements. The crystal structure recorded at 10 K after blue light irradiation reveals an heptacoordinated Mo(CN)₇ species originating from the light-induced cleavage of one Mo-CN bond, concomitant with the photoinduced formation of a paramagnetic signal. When this complex is heated to 70 K, it returns to its original diamagnetic ground state, demonstrating full reversibility. The photomagnetic properties show a partial conversion into a triplet state possessing significant magnetic anisotropy, which is in agreement with theoretical studies. Inspired by these results, we isolated the new compound [K(crypt-222)]₃ [Mo^IV (CN)₇ ]⋅3 CH₃ CN using a photochemical pathway, confirming that photodissociation leads to a stable heptacyanomolybdate(IV) species in solution.

Identical anomalous Raman relaxation exponent in a family of single ion magnets: towards reliable Raman relaxation determination?

The results described herein suggest that the exponent n for the temperature dependence of the Raman relaxation process in the series of solid-state diluted isostructural Ln^III SIMs should be identical.

Correlating magnetic anisotropy with [Mo(CN)7]4− geometry of MnII–MoIII magnetic frameworks

The magnetic coercivity of four new heptacyanomolybdate(iii)-based coordination polymers is correlated with the geometry of the [Mo^III(CN)₇]⁴⁻ anion and the cyanide bridging pattern of the framework.

A Photomagnetic Sponge: High-Temperature Light-Induced Ferrimagnet Controlled by Water Sorption

"Converting" light energy to magnetization is the attribute of molecule-based compounds called photomagnets and is inaccessible for conventional magnetic solids. The design and synthesis of such compounds, however, is a formidable challenge, and only a few examples are known, all with rather low magnetic ordering temperatures well below the boiling point of liquid nitrogen. Herein, a cyanide-bridged coordination polymer, {[Mn^II(imidazole)]₂[W^IV(CN)₈]} _n, exhibiting the highest light-induced magnetic ordering temperature ever observed and a magnetic hysteresis loop up to 90 K is reported. The photomagnetic effect results from the blue light excitation (450 nm) of the constituent octacyanotungstate(IV) moiety, which then couples magnetically with manganese(II), resulting in light-induced ferrimagnetic ordering. The reported coordination framework shows also outstanding water sorption properties that are strongly correlated with the photomagnetic functionality. The photoswitching observed in the anhydrous state is completely quenched by the reversible capture of water, with the fully hydrated phase becoming practically non-photomagnetic.

Octacyanidotungstate(IV) Coordination Chains Demonstrate a Light-Induced Excited Spin State Trapping Behavior and Magnetic Exchange Photoswitching

A huge increase in the magnetization of two coordination chains based on tetravalent octacyanidometalates (W^IV and Mo^IV ) is observed on irradiation with 436 nm light, while no such behavior is observed for the Nb^IV analogue. A photomagnetic response based solely on [W^IV (CN)₈ ]^4- is demonstrated for the first time. The observed behavior is attributed to the light-induced excited spin state trapping (LIESST) effect at the octacyanidometalate, and to the resulting magnetic exchange ON/OFF photoswitching between the Mn^II center and the photoinduced high-spin (S=1) W^IV or Mo^IV centers.

Systematic Study of Open-Shell Trigonal Pyramidal Transition-Metal Complexes with a Rigid-Ligand Scaffold

A family of distorted trigonal pyramidal transition-metal complexes [M^II (N₃ N)Li(THF)] (M=Mn, Fe, Co, Ni) have been studied as candidates for mononuclear single-molecule magnets. Magnetic anisotropy of the family depends on the electronic configuration of the central ion, with the Co analogue exhibiting pronounced SMM behavior.

Impact of immunosuppressive treatment on the cardiovascular system in patients after hand transplantation

BACKGROUND

Cardiovascular disease is a major cause of mortality in solid organ allograft recipients. Hand transplantation is not a lifesaving procedure, thus the effect of long-term immunosuppression on the cardiovascular system in these patients should be monitored. The aim of this study was to evaluate the morphology and function of heart and blood vessels in patients after hand transplantation.

METHODS

The study included 5 patients at ages 32 to 58 years, mean 39 years, who underwent hand transplantation between 2006 and 2010. Immunosuppressive treatment included basiliximab in induction and tacrolimus, mycophenolate mofetil, and prednisone. Cardiac status was assessed by echocardiography (according to the American Society of Echocardiography) and cardiac biomarkers. Blood vessels were estimated by carotid intima-media thickness, pulse wave velocity, and brachial artery flow-mediated dilatation (FMD). The examinations were performed at 28 to 79 (mean 43) months after transplantation.

RESULTS

Cardiovascular risk factors were observed in all patients after transplantation: 2 had insulin-dependent diabetes, 3 developed dyslipidemia and hypertension, 2 had chronic kidney disease stage 3. Concentric left ventricular hypertrophy was found in 1 and ventricular concentric remodeling in 4 patients. Impaired diastolic function (E/e' > 8) was observed in 2 patients. The index volume of the left atrium was higher in all patients. The cardiac biomarkers N-terminal pro-brain natriuretic peptide, C-reactive protein, and troponins were within normal range. Carotid intima-media thickness was higher in 1 patient and normal in 4 patients. Arterial stiffness measured by pulse wave velocity was not increased in all patients. Native brachial artery FMD response, an index of endothelium-dependent function, was abnormal in 2 patients, but in the transplanted extremity FMD was abnormal in 4 patients.

CONCLUSIONS

Pathologic changes in cardiac structures were found in all patients, but the arterial wall changes and endothelial dysfunction were observed in some patients. Patients after hand transplantation are at higher risk for cardiovascular disease.

[Homocysteine as a nonlipid factor in the pathogenesis of atherosclerosis]

Genetic abnormalities in two metabolic steps in homocysteine degradation: transsulfuration and remetylation can cause raised plasma homocysteine concentration. Homocysteine appeared to be an independent arteriosclerotic risk factor in the coronary, cerebral and peripheral circulation and elevated homocysteine levels have been found in chronic renal failure patients undergoing hemodialysis treatment and in transplant patients as well. Homocysteine has a direct toxic effect on endothelial cells, reduces normal activation of protein C by endothelial cells, increases the binding of Lp(a) to plasmin-modified fibrin, induces tissue factor procoagulant activity and inhibits the cofactor activity of thrombomodulin. Treatment with folic acid and piridoxine can lower the high level of homocysteine and should be associated with a clinical benefit.

[Treatment with human recombinant erythropoietin and nutritional status of patients on lon term dialysis]

In order to assess the effect of long term erythropoietin (EPO) therapy on the nutritional status of hemodialysed (HD) patients 2 groups of HD patients were studied: I-EPO treated for 72 +/- 8 mo, 12 patients, HD for 138 +/- 66 mo, II-control group, 14 patients with Ht 30%, HD for 121 +/- 35 mo. At the onset and after 6 years of follow up patients underwent the following examination: length, body weight, body mass index, body fat stores, arm muscle circumference and total serum protein, serum albumin, lymphocyte count, creatinine, urea, cholesterol and PTH. In EPO group mean BMI, body fat, arm muscle circumference, visceral protein and total lymphocyte count were not change. In control group the decrease in height, body weight, BMI, body fat stores, arm muscle circumference and albumin were observed. Elevation of PTH estimated in half of patients in EPO group and 75% of patients in control group could influence the nutritional status of hemodialysed patients.

CONCLUSION

1. Nutritional status of majority of hemodialysed patients was not change during six years EPO therapy. 2. Non EPO treated patients showed the decrease of anthropometric measurements and serum albumin.

[The effect of long term erythropoietin treatment on levels of free amino acids in patients with long term hemodialysis]

In order to assess the effect of erythropoietin (Epo) treatment on amino acids profile in hemodialysis patients (HD pts) 2 groups of pts were analyzed: I-12 pts HD for 146 +/- 71 months, Epo treated for 64 +/- 10 months, II-17 pts HD for 120 +/- 39 months, non Epo treated, mean Hb 11.5 +/- 1.2 g/dl. Controls consisted of 11 healthy individuals. Amino acids were estimated by HPLC OPA method. In group I blood levels of leucine (p < 0.03), valine (p < 0.002) were decreased and alanine (p < 0.05) was increased when compared to controls. In this group, blood levels of methionine, tyrosine and asparagine were elevated (p < 0.04) when compared to group II but they were lower (about 30%) then in controls. In group II pts showed reduced levels of valine (p < 0.008), leucine (p < 0.001), methionine (p < 0.0001), tyrosine (p < 0.003), asparagine (p < 0.04), whereas serine, glutamate and alanine (p < 0.04) were increased when compared to controls. Essential to nonessential amino acids ratios in group I, II and controls were as follows: 0.17; 0.12; 0.49 respectively. There were not substantial differences in amino acids in pts with elevated or normal PTH level in both HD groups. Long term EPO treatment only partially corrected changes in amino acids levels in pts with chronic renal failure.

Effect of parathyroid hormone on energy metabolism of skeletal muscle

Clinical states with primary or secondary hyperparathyroidism are associated with muscle dysfunction, suggesting that parathyroid hormone (PTH) may affect muscle metabolism. The present study examined the effect of 1-84 PTH and its amino-terminal fragment (1-34 PTH) on energy production, transfer, and utilization by skeletal muscle. Rats weighing 150 to 200 g were injected intraperitoneally with 1-84 or 1-34 PTH, 200 U/day, for 4 days, and control animals received vehicle only. The effect of the simultaneous administration of a calcium channel blocker, verapamil, was examined also. The muscle content of inorganic phosphorus, creatine phosphate, and adenine nucleotides were significantly (P less than 0.01) lower in the PTH-treated rats than in control animals. The hormone significantly reduced mitochondrial oxygen consumption without altering ADP:0 ratio, indicating reduced phosphorylation. Both 1-84 and 1-34 PTH produced significant (P less than 0.01) reduction in the activities of mitochondrial and myofibrillar CPK, and mitochondrial MgATPase. 1-84 PTH reduced the activity of myofibrillar CaATPase as well. There was a significant (P less than 0.01) increment in muscle uptake of 45Ca in the 1-84 PTH-treated rats. Verapamil abolished all the effects of PTH. Our data demonstrate that both 1-84 and 1-34 PTH impair energy production, transfer, and utilization. These biochemical derangements may, at least in part, underlie the myopathy observed in conditions associated with excess PTH.

Effect of parathyroid hormone on myocardial energy metabolism in the rat

This study examined the effect of parathyroid hormone (PTH) on myocardial energy production, transfer, and utilization. Rats (150 to 200 g) were injected with 1-84 PTH, 200 U/day i.p., or 1-34 PTH, 200 or 300 U/day i.p., for 4 days. Control animals received the vehicle only. The effect of the simultaneous administration of calcium channel blocker, verapamil, was also examined. Myocardial contents of Pi, ATP, and CP were significantly (P less than 0.01) lower in the 1-84 PTH-treated rats than in control animals. Both 1-84 PTH and 1-34 significantly (P less than 0.01) reduced mitochondrial oxygen consumption without altering ADP:O ratio indicating reduced phosphorylation. 1-84 and 1-34 PTH significantly (P less than 0.01) reduced the activities of mitochondrial and myofibrillar creatine phosphokinase and 1-84 PTH inhibited (P less than 0.01) the activities of mitochondrial Mg ATPase and those of myofibrillar Ca ATPase. There were significant (P less than 0.01) increments in myocardial 45Ca and in total calcium content in 1-84 PTH-treated rats. Verapamil abolished all the effects of 1-84 PTH. Similarly, inactivation of 1-84 PTH abolished its effects. Treatment with 1-84 PTH for 10 days was associated with a significant decrease in cardiac index and mean arterial pressure. Our data demonstrate that both 1-84 and 1-34 PTH impair energy production, transfer, and utilization. These biochemical derangements, if maintained, produce a decrease in cardiac index. It appears that the enhanced entry and the accumulation of calcium in the myocardium, either directly and/or indirectly, are responsible for the action of PTH on energy metabolism of the heart.