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The neutral holmium(III) oxalate octadecahydrate {[Ho 2 (ox) 3 (H 2 O) 6 ]·12H 2 O} n of mixed hexagonal/decagonal (6 3 ·10 3 ) 3D net topology shows important changes in the magnetocaloric efficiency upon dehydration/rehydration by heating and water vapor exposition to give the holmium(III) oxalate decahydrate {[Ho 2 (ox) 3 (H 2 O) 6 ]·4H 2 O} n of hexagonal (6 3 ) 2D net topology through the intermediacy of the elusive amorphous anhydrous compound {Ho 2 (ox) 3 } n .

We have prepared and characterized two Ru(III) compounds based on the 2,2'-biimidazole (H 2 biim) ligand, namely, a single complex of formula cis-[RuCl 2 (H 2 biim) 2 ]Cl·4H 2 O ( 1 ) and a racemic mixture of formula {cis-[RuCl 2 (H 2 biim) 2 ]Cl} 2 ·4H 2 O ( 2 ), which contains 50% of Ru(III) complex 1 . Both compounds crystallize in the monoclinic system with space groups C 2 and P 2 1 for 1 and 2 , respectively. These complexes exhibit the metal ion bonded to four nitrogen atoms from two H 2 biim molecules and two chloride ions, which balance part of the positive charges in a distorted octahedral geometry. Significant differences are observed in their crystal packing, which leads to the observation of differences in their respective magnetic behaviors. Despite having imidazole rings in both compounds, π-π stacking interactions occur only in the crystal structure of 2 , and the shortest intermolecular Ru···Ru separation in 2 is consequently shorter than that in 1 . Variable-temperature dc magnetic susceptibility measurements performed on polycrystalline samples of 1 and 2 reveal different magnetic behaviors at low temperatures: while 1 behaves pretty much as a magnetically isolated mononuclear Ru(III) complex with S = 1/2, 2 exhibits the behavior of an antiferromagnetically coupled system with S = 0 and a maximum in the magnetic susceptibility curve at approximately 3.0 K.

The ability of mononuclear first-row transition metal complexes as dynamic molecular systems to perform selective functions under the control of an external stimulus that appropriately tunes their properties may greatly impact several domains of molecular nanoscience and nanotechnology. This study focuses on two mononuclear octahedral cobalt(ii) complexes of formula {[Co II (HL) 2 ][Co II (HL)L]}(ClO 4 ) 3 ·9H 2 O (1) and [Co II L 2 ]·5H 2 O (2) [HL = 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine], isolated as a mixed protonated/hemiprotonated cationic salt or a deprotonated neutral species. This pair of pH isomers constitutes a remarkable example of a dynamic molecular system exhibiting reversible changes in luminescence, redox, and magnetic (spin crossover and spin dynamics) properties as a result of ligand deprotonation, either in solution or solid state. In this last case, the thermal-assisted spin transition coexists with the field-induced magnetisation blockage of "faster" or "slower" relaxing low-spin Co II ions in 1 or 2, respectively. In addition, pH-reversible control of the acid-base equilibrium among dicationic protonated, cationic hemiprotonated, and neutral deprotonated forms in solution enhances luminescence in the UV region. Besides, the reversibility of the one-electron oxidation of the paramagnetic low-spin Co II into the diamagnetic low-spin Co III ion is partially lost and completely restored by pH decreasing and increasing. The fine-tuning of the optical, redox, and magnetic properties in this novel class of pH-responsive, spin crossover molecular nanomagnets offers fascinating possibilities for advanced multifunctional and multiresponsive magnetic devices for molecular spintronics and quantum computing such as pH-effect spin quantum transformers., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Highly anisotropic single-molecule magnets (SMMs) have attracted much interest in the field of molecular magnetism because of their spin features and potential technological applications. Additionally, a great effort has been devoted to the functionalization of such molecule-based systems which are made with ligands containing functional groups suitable to connect SMMs to junction devices or to perform their grafting on surfaces of different substrates. We have synthesized and characterized two lipoic acid-functionalized and oxime-based Mn(III) compounds, of formula [Mn 6 (μ 3 -O) 2 (H 2 N-sao) 6 (lip) 2 (MeOH) 6 ][Mn 6 (μ 3 -O) 2 (H 2 N-sao) 6 (cnph) 2 (MeOH) 6 ]}·10MeOH ( 1 ) and [Mn 6 (μ 3 -O) 2 (H 2 N-sao) 6 (lip) 2 (EtOH) 6 ]·EtOH·2H 2 O ( 2 ) [H 2 N-saoH 2 = salicylamidoxime, lip = lipoate anion, cnph = 2-cyanophenolate anion]. Compound 1 crystallizes in the space group P ī of the triclinic system and 2 crystallizes in the space group C2/c of the monoclinic system. In the crystal, neighboring Mn 6 entities are linked using non-coordinating solvent molecules, which are H-bonded to N atoms of -NH 2 groups of amidoxime ligand. In addition, Hirshfeld surfaces of 1 and 2 were calculated to study the variety of intermolecular interactions and the different levels of importance that take place in their crystal lattice; this type of computed study is the first time performed on Mn 6 complexes. The study of the magnetic properties of 1 and 2 through dc magnetic susceptibility measurements reveals the coexistence of ferromagnetic and antiferromagnetic exchange couplings between the Mn(III) metal ions in both compounds, the latter being the predominant magnetic interaction. A spin S = 4 value of the ground state was obtained using isotropic simulations of the experimental magnetic susceptibility data for both 1 and 2 . Ac magnetic susceptibility measurements show features typical of slow relaxation of the magnetization in 1 and 2 , which indicate that SMM behavior takes place in both compounds.

The cobalt(II)-mediated self-assembly of the potentially tris(chelating) N , N '-2,2'-(4,4'-bithiazole)bis(oxamate) (dabtzox) ligand gives a new metal-organic supramolecular nanomagnet of formula K 6 Co 3 (dabtzox) 3 ·8H 2 O·MeOH ( 1 ) featuring a unique linear triple-stranded trinuclear structure of the helicate type.

A new series of cyanido-bridged {Fe III Ln III } 2 neutral molecular squares of general formula [Fe{HB(pz) 3 }(CN)(μ-CN) 2 Ln(NO 3 ) 2 (pyim)(Ph 3 PO)] 2 ·2CH 3 CN [Ln = Ce (1), Pr (2), Nd (3), Gd (4), Tb (5), Dy (6) and Er (7); {HB(pz) 3 } - = hydrotris(pyrazolyl)borate, pyim = 2-(1 H -imidazol-2-yl)pyridine and Ph 3 PO = triphenylphosphine oxide] were obtained by reacting the low-spin [Fe{HB(pz) 3 }(CN) 3 ] - species with the preformed [Ln III (pyim)(NO 3 ) 2 (pyim)(Ph 3 PO)] + complex anions (generated in situ by mixing the nitrate salt of each Ln(III) ion with pyim and Ph 3 PO molecules). Single-crystal X-ray diffraction studies show that 1-7 are isostructural compounds that crystallize in the triclinic P 1̄ space group. Their crystal structures consist of centrosymmetric cyanido-bridged {Fe III Ln III } 2 molecular squares where two [Fe{HB(pz) 3 }(CN) 3 ] - units adopt bis-monodentate coordination modes towards two [Ln III (pyim)(NO 3 ) 2 (pyim)(Ph 3 PO)] + moieties. The cis -oriented convergent sites from both low-spin Fe III and Ln III fragments form a quasi square-shaped molecule in which the 3d and 4f ions alternatively occupy the corners of the square. Both Fe III ions show a distorted octahedral surrounding ( C 3v symmetry), whereas the Ln III ions exhibit a distorted muffin-like geometry ( C s symmetry) in 1-7. The intramolecular Fe III ⋯Ln III distances across the two cyanido-bridges range from ca. 5.48/5.46 up to ca. 5.58/5.61 Å. The molecular squares in 1-7 are interlinked through hydrogen bonds, weak π⋯π stacking and very weak C-H⋯π type interactions into three-dimensional supramolecular networks. The analysis of the solid-state direct-current (dc) magnetic susceptibility data of 1-7 in the temperature range 1.9-300 K reveals the occurrence of weak intra- and intermolecular antiferromagnetic interactions. The small intramolecular antiferromagnetic couplings in 4 compare well with those previously reported for parent systems. Although the coexistence of the spin-orbit coupling (SOC) of the low-spin iron(III) and lanthanide(III) ions in the remaining compounds together with the ligand field effects mask the visualization and make difficult the evaluation of the possible magnetic interactions in them, we were able to do it through a SOC model applied on exact or effective Hamiltonians. Frequency-dependent alternating current magnetic susceptibility signals in the temperature range 2.0-9.0 K under zero and non-zero static fields were observed for 5-7 which indicate slow magnetic relaxation (SMM) behavior. The usual absence of χ '' M maxima moved us to estimate their energy barriers through ln( χ '' M / χ ' M ) vs. 1/ T plots, obtaining values from 25 to 40 cm -1 .

The coexistence of field-induced blockage of the magnetization and significant magnetocaloric effects in the low-temperature region occurs in a mononuclear holmium(III) diethylenetriamine- N , N , N ', N ″, N ″-pentaacetate complex, whose gadolinium(III) analogue is a commercial MRI contrast agent. Both properties make it a suitable candidate for cryogenic magnetic refrigeration, thus enlarging the variety of applications of this simple class of multifunctional molecular nanomagnets.

Photovoltaic panels can be colonized by a highly diverse microbial diversity, despite life-threatening conditions. Although they are distributed worldwide, the microorganisms living on their surfaces have never been profiled in tropical regions using 16S rRNA high-throughput sequencing and PICRUst metagenome prediction of functional content. In this work, we investigated photovoltaic panels from two cities in southeast Brazil, Sorocaba and Itatiba, using these bioinformatics approach. Results showed that, despite significant differences in microbial diversity (p < 0.001), the taxonomic profile was very similar for both photovoltaic panels, dominated mainly by Proteobacteria, Bacteroidota and lower amounts of Cyanobacteria phyla. A predominance of Hymenobacter and Methylobacterium-Methylorubrum was observed at the genus level. We identified a microbial common core composed of Hymenobacter, Deinococcus, Sphingomonas, Methylobacterium-Methylorubrum, Craurococcus-Caldovatus, Massilia, Noviherbaspirillum and 1174-901-12 sharing genera. Predicted metabolisms focused on specific genes associated to radiation and desiccation resistance and pigments, were detected in members of the common core and among the most abundant genera. Our results suggested that taxonomic and functional profiles investigated were consistent with the harsh environment that photovoltaic panels represent. Moreover, the presence of stress genes in the predicted functional content was a preliminary evidence that microbes living there are a possibly source of metabolites with biotechnological interest., (© The Author(s) 2021. Published by Oxford University Press on behalf of FEMS. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Two novel copper(II) complexes of formulas {[Cu(4-Hmpz) 4 ][Cu(4-Hmpz) 2 (µ 3 -ox- κ 2 O 1 , O 2 : κO 2' : κO 1' )(ClO 4 ) 2 ]} n ( 1 ) and {[Cu(3,4,5-Htmpz) 4 ] 2 [Cu(3,4,5-Htmpz) 2 (µ 3 -ox- κ 2 O 1 , O 2 : κO 2' : κO 1' )(H 2 O)(ClO 4 )] 2 [Cu 2 (3,4,5-Htmpz) 4 (µ-ox- κ 2 O 1 , O 2 : κ 2 O 2' , O 1' )]}(ClO 4 ) 4 ·6H 2 O ( 2 ) have been obtained by using 4-methyl-1 H -pyrazole (4-Hmpz) and 3,4,5-trimethyl-1 H -pyrazole (3,4,5-Htmpz) as terminal ligands and oxalate (ox) as the polyatomic inverse coordination center. The crystal structure of 1 consists of perchlorate counteranions and cationic copper(II) chains with alternating bis(pyrazole)(µ 3 - κ 2 O 1 , O 2 : κO 2' : κO 1' -oxalato)copper(II) and tetrakis(pyrazole)copper(II) fragments. The crystal structure of 2 is made up of perchlorate counteranions and cationic centrosymmetric hexanuclear complexes where an inner tetrakis(pyrazole)(µ- κ 2 O 1 , O 2 : κ 2 O 2' , O 1' -oxalato)dicopper(II) entity and two outer mononuclear tetrakis(pyrazole)copper(II) units are linked through two mononuclear aquabis(pyrazole)(µ 3 - κ 2 O 1 , O 2 : κO 2' : κO 1' -oxalato)copper(II) units. The magnetic properties of 1 and 2 were investigated in the temperature range 2.0-300 K. Very weak intrachain antiferromagnetic interactions between the copper(II) ions through the µ 3 -ox- κ 2 O 1 , O 2 : κO 2' : κO 1' center occur in 1 [ J = -0.42(1) cm -1 , the spin Hamiltonian being defined as H = - J∑ S 1,i · S 2,i +1 ], whereas very weak intramolecular ferromagnetic [ J = +0.28(2) cm -1 ] and strong antiferromagnetic [ J' = -348(2) cm -1 ] couplings coexist in 2 which are mediated by the µ 3 -ox- κ 2 O 1 , O 2 : κO 2' : κO 1' and µ-ox- κ 2 O 1 , O 2 : κ 2 O 2' , O 1' centers, respectively. The variation in the nature and magnitude of the magnetic coupling for this pair of oxalato-centered inverse copper(II) complexes is discussed in the light of their different structural features, and a comparison with related oxalato-centered inverse copper(II)-pyrazole systems from the literature is carried out.

The coexistence of field-induced slow magnetic relaxation and moderately large magnetocaloric efficiency in the supra-Kelvin temperature region occurs in the 2D compound [Gd(ox) 3 (H 2 O) 6 ] n ·4nH 2 O (1), a feature that can be exploited in the proof-of-concept design of a new class of slow-relaxing magnetic materials for cryogenic magnetic refrigeration.

Thermal-assisted spin crossover and field-induced slow magnetic relaxation coexist in the solid state for the mononuclear cobalt(ii) complex with the non-innocent 2,6-bis(N-4-methoxyphenylformimidoyl)pyridine ligand. One-electron oxidation of the paramagnetic low-spin Co II ion (S Co = 1/2) to the diamagnetic low-spin Co III ion (S Co = 0) leads to the electroswitching of the slow magnetic relaxation in acetonitrile solution.

We herein present the synthesis, spectroscopic analysis, description of the crystal structures and magnetic properties of four new complexes of the formula [{Cu(opba)(H 2 O) 1.2 }{Cu(dmphen)(SCN)} 2 ]·dmf (1), [{Cu(opba)} 2 {Cu(dmphen)Cl} 4 ]·1.5dmf·2.5dmso (2), [{Cu(opba)} 2 {Cu(dmphen)Br} 4 ]·dmf·2.3dmso (3) and [{Cu(opba)}{Cu(dmphen)(dca)} 2 ] n (4) [H 4 opba = N,N'-1,2-phenylenebis(oxamic acid), dmphen = 2,9-dimethyl-1,10-phenanthroline and dca = dicyanamide anion]. 1 is a neutral tricopper(ii) complex where an inner [Cu(opba)] 2- fragment adopts a bis-bidentate coordination mode towards two outer [Cu(dmphen)(NCS)] + units. 2 and 3 are bis-trinuclear species where two oxamato-bridged [Cu(opba){Cu(dmphen)X} 2 ] [X = Cl - (2) and Br - (3)] tricopper(ii) entities are connected by two single X ions involving the central and one of the peripheral copper(ii) ions. 4 is a neutral chain made up of oxamato-bridged [Cu(opba){Cu(dmphen)(dca)} 2 ] fragments linked through a single end-to-end dicyanamide ligand that connects the central copper(ii) ion with one of the peripheral copper(ii) ions. Magnetic susceptibility measurements on polycrystalline samples of 1-4 in the temperature range 1.9-300 K show the occurrence of strong antiferromagnetic interactions between the copper(ii) ions through the oxamate bridge [J = -328(2) (1), -288(2) (2), -431(2) (3) and -370(1) cm -1 (4), the Hamiltonian being defined as H = -J(S 1 ·S 2 + S 1 ·S 3 )] and a weak ferromagnetic coupling across the equatorial-axial exchange pathway provided by the single halide bridge [j = +3.08(3) (2) and +2.34(1) cm -1 (3)]. These values are analyzed by simple orbital symmetry considerations and compared with those reported in the literature for polynuclear copper(ii) complexes with these bridging ligands.

The compound (NBu4)4[ZnII{ReIVCl4(μ-ox)}3] (1) [NBu4+ = tetra-n-butylammonium cation and ox2- = oxalate dianion] is the first example of an oxalato-bridged ZnII system coordinated to a 5d metal ion that exhibits slow relaxation of magnetisation.

The preparation and spectroscopic and structural characterization of three cobalt(II) complexes of formulas [Co(tppz) 2 ](dca) 2 (1), [Co(tppz) 2 ][Co(NCS) 4 ]·MeOH (2), and [Co(tppz) 2 ][Co(NCO) 4 ]·2H 2 O (3) [tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine and dca = dicyanamide] are reported here. Compounds 1-3 have in common the presence of the cationic [Co(tppz) 2 ] 2+ entity where each mer-tridentate tppz ligand coordinates to the cobalt(II) ion equatorially through two pyridyl donors and axially via the pyrazine, completing the six-coordination. The electroneutrality is achieved by the organic dca group (1) and the anionic tetrakis(thiocyanato-κN)cobaltate(II) (2) and tetrakis(cyanato-κN)cobaltate(II) (3) complexes. Direct current (dc) magnetic susceptibility measurements of 1 in the temperature range 1.9-400 K show the occurrence of a thermally induced spin crossover behavior of the [Co(tppz) 2 ] 2+ unit from a high spin (S = 3/2) at higher temperatures to a low-spin (S = 1/2) at lower temperatures, with the low spin phase being reached at T ≤ 200 K. X-band electron paramagnetic resonance (EPR) measurements in solution at low temperatures were used to characterize the low spin state. An analytical expression based on the combination of the spin-orbit coupling and both first- and second-order Zeeman effects for a d 7 electronic configuration was used to fit the magnetic data of 1, the values of the best-fit parameters being C vib = 0.1367(9), λ = -168(2) cm -1 , α = 1.12(1), Δ = 1626(15) cm -1 , and g LS = 2.12(1). The magnetic behavior of the four-coordinate cobalt(II) ions [Co(NCS) 4 ] 2- (2) and [Co(NCO) 4 ] 2- (3) with a 4 A 2 ground state overlaps with the spin crossover of the [Co(tppz) 2 ] 2+ entity, the abrupt decrease of the χ M T product below 15.0 K being due to zero-field splitting effects between the spin components |±1/2> and |±3/2>. The combined analysis of the dc magnetic data and the Q-band EPR spectra in the solid state of 2 and 3 led to the following sets of best-fit parameters: C vib = 0.105(5), λ = -170(4) cm -1 , α = 1.10(2), Δ = 1700(25) cm -1 , g LS = 2.10(1), g HS = 2.27(1), and |D| = 3.80(2) cm -1 (2) and C vib = 0.100(1), λ = -169(5) cm -1 , α = 1.10(3), Δ = 1500(30) cm -1 , g LS = 2.10(1), g HS = 2.28(1), and |D| = 4.30(2) cm -1 (3). Some evidence of slowing of the relaxation of the magnetization has been found in the out-of-phase ac signal at very low temperatures under applied dc fields of 0.1-0.4 T for 3, suggesting the occurrence of single-ion magnet behavior of its [Co(NCO) 4 ] 2- anionic entity.

The suitability of the system [Fe(4,4'-bipy)(H(2)O)(2)(NCX)(2)].(4,4'-bipy), where 4,4'-bipy stands for 4,4'-bipyridine and X = S (1) and Se (2), as a precursor for the synthesis of new polymeric spin-crossover compounds has been studied. The reaction of 1 or 2 with bt (2,2'-bithiazoline) afforded the polymeric compounds of formula [Fe(4,4'-bipy)(bt)(NCX)(2)] (X = S (3), Se (4)). Compounds 3 and 4 are isostructural, but only the crystal structure of 3 has been fully determined. It crystallizes in the orthorhombic system, Fdd2 space group, Z = 24, with a = 38.962(8) A, b = 11.545(2) A, c = 30.889(6) A, V = 13895(5) A(3). The structure consists of linear chains constituted by trans-4,4'-bipy linked iron(II) ions; two cis equatorial positions are occupied by two pseudohalide ligands, and the remaining positions are filled by the bidentate bt ligand. Investigation of their magnetic properties and Mössbauer spectra has revealed the occurrence of a low-spin (LS) <--> high-spin (HS) conversion involving 12% (3, S) and 20% (4, Se) of the Fe(II) ions. The thermal variation of the HS fraction is gradual with onset temperatures as low as 60 K. A theoretical approach based on the Ising-like model, completed with molecular vibrations, through harmonic oscillators, fits the data successfully, leading to an energy gap of 65 cm(-1) (3) and 86 cm(-1) (4) between the lowest LS and HS levels, and an average vibration frequency ohgrmacr;(LS) of 382 cm(-1) (3) and 365 cm(-1) (4) in the LS state. The ca. 1.05 omega(LS(3))/omega(LS(4)) ratio is close to the ca. 1.09 Se/S molar mass ratio. The simple electrovibrational Ising-like model permits us to explain, for the first time, a mass effect through the molecular vibrations in a spin-crossover complex that is in the unusual situation of equienergy among the HS and LS states.

[Fe(abpt)2(N(CN)2)2] (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) represents the first example of an iron(II) spin-crossover compound containing dicyanamide ligand, [N(CN)(2)](-), as a counterion. It shows an incomplete two-step spin transition with around 37% of HS molecules trapped in the low-temperature region when standard cooling or warming modes, i.e., 1-2 K min(-)(1), were used. The temperature, T(1/2) approximately 86 K, at which 50% of the conversion takes place, is one of the lowest temperatures observed for an iron(II) spin-crossover compound. Quenching experiments at low temperatures have shown that the incomplete character of the conversion is a consequence of slow kinetics. The quenched HS state relaxes back to the LS state displaying noticeable deviation from a single-exponential law. The rate of relaxation was evaluated in the range of temperatures 10-60 K. In the upper limit of temperatures, where thermal activation predominates, the activation energy and the pre-exponential parameter were estimated as E(a) approximately 280 cm(-)(1) and A(HL) approximately 10 s(-)(1), respectively. The lowest value of k(HL) around 1.2 x 10(-)(4) s(-)(1) (T = 10 K) was obtained in the region of temperatures where tunneling predominates. A quantitative light induced excited spin state trapping (LIESST) effect was observed, and the HS --> LS relaxation in the range of temperatures 5-52.5 K was studied. From the Arrhenius plot the two above-mentioned characteristic regimes, thermal-activated (E(a) approximately 431 cm(-)(1) and A(HL) approximately 144 s(-)(1)) and tunneling (k(HL) approximately 1.7 x 10(-)(6) s(-)(1) at 5 K), were characterized. The crystal structure was solved at room temperature. It crystallizes in the triclinic P&#95;1 space group, and the unit cell contains a centrosymmetric mononuclear unit. Each iron atom is in a distorted octahedral environment with bond distances Fe-N(1) = 2.216(2) A, Fe-N(2) = 2.121(2) A, and Fe-N(3) = 2.160(2) A for the pyridine, triazole, and dicyanamide ligands, respectively.