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Highlights A facile chelated coupled pyrolysis strategy was reported to prepare Mn single-cluster Hg0 adsorbent. The nitrogen-containing group in biomass determined the size of atomically dispersed manganese. The presence of oxygen and small size Mn clusters in biochar promoted Hg0 adsorption.

Carbon-based materials have been widely used in gaseous pollutant removal because of their sufficient surface functional groups; however, its removal efficiency for elemental mercury (Hg0) is low. In this study, we fabricated biomass using a chelated coupled pyrolysis strategy and further constructed the regulated adsorption sites for gaseous Hg0 uptake. A series of Mnδ-N2O2/BC with different manganese cluster sizes demonstrated that manganese clusters anchored on biochar acted as highly active and durable adsorbents for Hg0 immobilization, which increased the adsorption efficiency of Hg0 by up to 50%. Shrimp- and crab-based biochar adsorbents exhibited excellent Hg0 removal because of their chitosan-like structure. In particular, small Mn clusters and oxygen species around the defect led to a boost in the Hg0 adsorption by carbon. The results of density functional theory calculation revealed that the presence of oxygen in the carbon skeleton can tune the electrons of small-sized Mn clusters, thereby promoting the affinity of mercury atoms. The newly developed Mnδ-N2O2/BCshrimp had an adsorption capacity of 7.98–11.52 mg g−1 over a broad temperature range (50–200 °C) and showed a high tolerance to different industrial flue gases (H2O, NO, HCl, and SO2). These results provide novel green and low-carbon disposal methods for biomass resource utilization and industrial Hg0 emission control. Highlights: A facile chelated coupled pyrolysis strategy was reported to prepare Mn single-cluster Hg0 adsorbent. The nitrogen-containing group in biomass determined the size of atomically dispersed manganese. The presence of oxygen and small size Mn clusters in biochar promoted Hg0 adsorption. [ABSTRACT FROM AUTHOR]

The paper reports that silicon with nanoclusters of manganese atoms has unique electrical, photoelectric, magnetic, and photomagnetic properties that are absent in ordinary doped semiconductor materials. The samples revealed an anomalously high impurity photosensitivity in the region of λ = 1–3 μm, a large negative magnetoresistance at room temperature, and new thermomagnetic and photomagnetic effects, which were observed in the same sample. The optimal electrophysical parameters of the samples were found. A unique set of the observed physical effects allows the creation of fundamentally new multifunction sensors of physical quantities based on these materials. [ABSTRACT FROM AUTHOR]

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Graphical abstract Highlights • Controlled synthesis of RHO and SAPO-34 and RHO&SAPO-34 silicoaluminaphosphates is mediate by Mn cluster additives. • High selectivity for the C 2-4= light olefins (90.2%) was obtained over RHO&SAPO-34 catalysts. • RHO&SAPO-34 showed good durability during the DTO, due to its high acidic density (over 4.5 h). Abstract RHO- and CHA-type silicoaluminaphosphates have played an essential role in the global olefin production, e.g., dimethylether to light olefin process (DTO). In this work, we report a simple synthetic protocol to selectively acquire pure RHO and SAPO-34 and RHO&SAPO-34 silicoaluminaphosphates, which is controllable mediated by the thiolate-capped manganese cluster additives. These prepared silicoaluminaphosphates are well characterized by powder X-ray diffraction (XRD), ammonia-temperature programmed desorption (NH 3 -TPD), and as well as N 2 -physical adsorption. They are investigated in the DTO catalysis. The selectivity for the C 2-4= light olefins over the RHO&SAPO-34 catalysts is up to 90.2%, which is much higher than these over the RHO (65.5%) and SAPO-34 (69.0%) silicoaluminaphosphates. Especially, the selectivity for ethylene is two times of these over RHO and SAPO-34. It is beneficial to selectively give rise to ethylene by the dual cycle hydrocarbon-pool mechanism in the DTO reactions, as the RHO&SAPO-34 showed much stronger acidic density, both in the strong acidic sites (0.966 mmol g−1) and weak acidic sites (0.575 mmol g−1), than the RHO and SAPO-34. Finally, the RHO&SAPO-34 also performs longer lifetime and durability (ca. 4.5 h) than the corresponding SAPO-34 and RHO silicoaluminaphosphates (ca. 1 h and 4 h), which is mainly due to slow formation of the carbon deposition over its strong acid density. [ABSTRACT FROM AUTHOR]

The natural Mn4Ca cluster in photosystem II serves as a blueprint to develop artificial water‐splitting catalysts for the generation of solar fuel in artificial photosynthesis. Although significant advances have recently been achieved, it remains a great challenge to prepare robust artificial Mn4Ca clusters that precisely mimic the structure and function of the biological catalyst. Herein, we report the isolation and structural characterization of two Mn4CaO4 complexes with polar solvent molecules, acetonitrile or N,N‐dimethylformamide, which closely mimics the two water molecules on the calcium ion, as well as the oxidation states of the four manganese ions and the main geometric structure of the natural Mn4Ca cluster. These new artificial Mn4Ca complexes provide important chemical clues to understand the structure and mechanism of the biological system. [ABSTRACT FROM AUTHOR]

While the coordination chemistry of monometallic complexes and the surface properties of extended metal particles are well understood, the control of metal nanocluster formation has remained challenging. The isolation of discrete metal clusters provides an especially rare snapshot at the nanoscale of cluster growth. The synthesis and full characterization of the first early‐transition‐metal alkynyl cubane and the first μ3‐alkynyl Mn3 motif are reported. [ABSTRACT FROM AUTHOR]

Water electrolysis is among the simplest method for generating hydrogen as an alternative renewable fuel. A major challenge associated with this process is the development of cheap, simple, and environmentally benign catalysts that lead to a minimum overpotential for water oxidation. Inspired by the Mn4CaOx cluster that catalyzes water oxidation in photosystem II, described here is the synthesis and characterization of the manganese cluster [Mn12O12(O2CC6H2(OH)3)16(H2O)4] (Mn12TH) along with its electrocatalytic activity at pH 6. Electrochemical, spectroscopic, and electron microscopy studies show that Mn12TH is a homogeneous electrocatalyst for water oxidation and enables oxygen evolution with a reaction rate of 22 s−1, high Faradic efficiency (93 %), and an overpotential of only 74 mV, the lowest reported to date. Based on the electrochemical data, the organic ligands, which can be described as the second coordination sphere of the catalytic manganese core, play a key role in facilitating the oxidation process and accelerating the reaction. [ABSTRACT FROM AUTHOR]

Cyanobacteria and plants carry out oxygenic photosynthesis. They use water to generate the atmospheric oxygen we breathe and carbon dioxide to produce the biomass serving as food, feed, fibre and fuel. This paper scans the emergence of structural and mechanistic understanding of oxygen evolution over the past 50 years. It reviews speculative concepts and the stepped insight provided by novel experimental and theoretical techniques. Driven by sunlight photosystem II oxidizes the catalyst of water oxidation, a hetero-metallic Mn4CaO5(H2O)4 cluster. Mn3Ca are arranged in cubanoid and one Mn dangles out. By accumulation of four oxidizing equivalents before initiating dioxygen formation it matches the four-electron chemistry from water to dioxygen to the one-electron chemistry of the photo-sensitizer. Potentially harmful intermediates are thereby occluded in space and time. Kinetic signatures of the catalytic cluster and its partners in the photo-reaction centre have been resolved, in the frequency domain ranging from acoustic waves via infra-red to X-ray radiation, and in the time domain from nano- to milli-seconds. X-ray structures to a resolution of 1.9 Å are available. Even time resolved X-ray structures have been obtained by clocking the reaction cycle by flashes of light and diffraction with femtosecond X-ray pulses. The terminal reaction cascade from two molecules of water to dioxygen involves the transfer of four electrons, two protons, one dioxygen and one water. A rigorous mechanistic analysis is challenging because of the kinetic enslaving at millisecond duration of six partial reactions (4e−, 1H+, 1O2). For the time being a peroxide-intermediate in the reaction cascade to dioxygen has been in focus, both experimentally and by quantum chemistry. Homo sapiens has relied on burning the products of oxygenic photosynthesis, recent and fossil. Mankind's total energy consumption amounts to almost one-fourth of the global photosynthetic productivity. If the average power consumption equalled one of those nations with the highest consumption per capita it was four times greater and matched the total productivity. It is obvious that biomass should be harvested for food, feed, fibre and platform chemicals rather than for fuel. [ABSTRACT FROM AUTHOR]

Two novel decametallic clusters displaying a supertetrahedral structural core are discussed, a homometallic compound [Mn III 9 Mn II (μ 4 -O) 4 (μ 3 -OMe) 3 (btH) 3 (ed) 3 (PhCO 2 ) 6 ]·6Η 2 Ο ( 1 ·6Η 2 Ο) (btH 3  = (±)-1,2,4-butanetriol; edH 2  = 1,2-ethanediol) and a heterometallic one [Mn III 6 Ca II 4 (μ 4 -O) 4 (μ 3 -Cl) 4 (pd) 6 Cl 2 (MeOH) 10 ] ( 2 ) (pdH 2  = 1,3-propanediol). In particular complex 1 ·6Η 2 Ο is a new member of an extended family of homometallic Mn 10 supertetrahedra which exhibits an unprecedented Mn III 9 Mn II oxidation state level. It is based on a supertetrahedral [Mn III 9 Mn II (μ 4 -O) 4 ] 21+ core with its peripheral ligation being completed by bridging alkoxy (OMe − , btH 2− , ed 2− ) and carboxylate (PhCO 2 − ) ligands. Complex 2 is a unique heterometallic analogue of the family of complexes displaying the well-known [Mn III 6 Mn II 4 (μ 4 -O) 4 ] 18+ supertetrahedral core in which the Mn II ions have been replaced by Ca II ions. The peripheral ligation of the heterometallic [Mn III 6 Ca II 4 (μ 4 -O) 4 ] 18+ core is completed by both bridging (μ 3 -Cl − and pd) and terminal (Cl − , MeOH) ligands. Magnetism studies revealed that complex 1 ·6Η 2 Ο displays dominant ferromagnetic exchange interactions and a large spin ground state value S T  = 23/2 whereas complex 2 exhibits exclusively ferromagnetic exchange interactions and the maximum possible spin ground state S T  = 12 for a complex consisting of six Mn III and four Ca II ions. [ABSTRACT FROM AUTHOR]

In this study, Cobalt-Manganese-Zinc nanoferrites with the formula Co x Mn 0.5−x Zn 0.5 Fe 2 O 4 with x = 0.0, 0.1, 0.3, and 0.5 prepared by chemical Co-precipitation method. Then the structure and morphology of the synthesized nanoparticles were characterized by X-ray diffraction (XRD) and transmitting electron microscopy (TEM), respectively. The XRD patterns indicated the formation of single-phased cubic structure of spinel ferrite in nanometer size with no minor phase. The TEM image showed the formation of nanoparticles with average size of about 40 nm and normal size distribution. The magnetic measurements of the nanoparticles were done at room temperature using a vibrating sample magnetometer (VSM). Results exhibited a super-paramagnetic like behavior for some of the samples. DC electrical resistivity measurements were carried out by two-probe technique from 25 to 250 °C and showed decreasing of the resistivity with temperature meanwhile passing a transition to form of a peak. The peaks values observed near the Curie temperatures of samples suggest that anomaly behavior can attributed to spin canting associated with the phase transition from para to ferromagnetic state at T C . [ABSTRACT FROM AUTHOR]

Four novel linear trinuclear manganese clusters [Mn 3 (L n ) 2 (CH 3 COO) 4 ] ( 1 , n = 1; 2 , n = 2; 3 , n = 3; 4 , n = 4. where HL 1 is 4-chloro-2-((2-(6-chloropyridin-2-yl)hydrazono)methyl)phenol, HL 2 is 4-bromo-2-((2-(6-chloropyridin-2-yl)hydrazono)methyl)phenol, HL 3 is 4-chloro-2-((2-(6-bromopyridin-2-yl)hydrazono)methyl)phenol, HL 4 is 4-bromo-2-((2-(6-bromopyridin-2-yl) hydrazono)methyl)phenol) were synthesized through solvothermal method. Complexes 1 – 4 were characterized by IR, and X-ray single-crystal diffraction. Complexes 1 – 4 are isomorphous compounds which are trinuclear linear manganese clusters. A detailed analysis of Hirshfeld surface and 2D fingerprint plots revealed that 1 – 4 were supported mainly by H⋯H, H⋯X (X = Cl, Br) and O⋯H intermolecular interactions. Magnetic properties of 1 – 4 have been studied. In additional, complex 3 showed highly intense electrochemicaluminescence (ECL) in DMF solution. [ABSTRACT FROM AUTHOR]

The electronic structure of manganese (Mn) cluster in photosystem II was investigated by electron paramagnetic resonance (EPR) spectroscopy. In order to determine the spin density distribution in magnetically coupled Mn in the S2 state Mn cluster, pulsed electron-electron double resonance (PELDOR) measurement was performed. The local environment of the Mn cluster was investigated by electron-nuclear double resonance (ENDOR). Using spin projections determined by PELDOR, ENDOR signals were assigned to the water molecules ligated to the Mn cluster. The location of a high-affinity Mn2+ site in apo-photosystem II, which is the initial site of photoactivation of the Mn cluster, was determined by PELDOR. [ABSTRACT FROM AUTHOR]

Understanding the structure of oxygen evolving complex (OEC) fully still remains a challenge. Lately computational chemistry with the data from more detailed X-ray diffraction (XRD) OEC structure, has been used extensively in exploring the mechanisms of water oxidation in the OEC (Gatt et al., J. Photochem. Photobiol. B 104(1-2), 80-93 2011). Knowledge of the oxidation states is very crucial for understanding the core principles of catalysis by photosystem II (PSII) and catalytic mechanism of OEC. The present study involves simulation studies of the X-band continuous wave electron-magnetic resonance (CW-EPR) generated S state signals, to investigate whether the data is in agreement with the four manganese ions in the OEC, being organised as a '3 + 1' (trimer plus one) model (Gatt et al., Angew. Chem. Int. Ed. 51, 12025-12028 2012; Petrie et al., Chem. A Eur. J. 21, 6780-6792 2015; Terrett et al., Chem. Commun. (Camb.) 50, 8-11 2014) or 'dimer of dimers' model (Terrett et al. 2016). The question that still remains is how much does each Mn ion contribute to the ' g2multiline' signal through its hyperfine interactions in OEC also to differentiate between the 'high oxidation state (HOS)' and 'low oxidation state (LOS)' paradigms? This is revealed in part by the structure of multiline (ML) signal studied in this project. Two possibilities have been proposed for the redox levels of the Mn ions within the catalytic cluster, the so called 'HOS' and 'LOS' paradigms (Gatt et al., J. Photochem. Photobiol. B 104(1-2), 80-93 2011). The method of data analysis involves numerical simulations of the experimental spectra on relevant models of the OEC cluster. The simulations of the X-band CW-EPR multiline spectra, revealed three manganese ions having hyperfine couplings with large anisotropy. These are most likely Mn centres and these clearly support the 'LOS' OEC paradigm model, with a mean oxidation of 3.25 in the S state. This is consistent with the earlier data by Jin et al. (Phys. Chem. Chem. Phys. (PCCP) 16(17), 7799-812 2014), but the present results clearly indicate that heterogeneity in hyperfine couplings exist in samples as typically prepared. [ABSTRACT FROM AUTHOR]

A manganese containing polyoxometalate (POM) [Mn 3 (H 2 O) 3 (SbW 9 O 33 ) 2 ] 12− ( 1 ) was synthesized and characterized in detail. The photocatalytic activity of 1 is definitely better than other manganese containing POM water oxidation catalysts reported so far according to oxygen yield, whereas the analogues [Mn 3 (H 2 O) 5 (PW 9 O 34 ) 2 ] 9− ( 2 ) and [Mn 3 (H 2 O) 3 (AsW 9 O 33 ) 2 ] 12− ( 3 ) show no to slight photocatalytic O 2 evolution amount. Meanwhile, the electrocatalytic activities of 1 - 3 were investigated in 80 mM pH 9.0 borate buffer, which follows the catalytic activity order of 1 > 2 > 3 . Multiple experiments including UV−vis absorption, catalysts aging experiments, tetra- n -heptylammonium nitrate (THpANO 3 ) toluene extraction, electrochemical experiments and capillary electrophoretic measurements results confirm that catalyst 1 is a homogeneous molecular catalyst. No Mn 2+ (aq.) or manganese oxide under the reaction conditions of photocatalytic and electrochemical water oxidation was detected. [ABSTRACT FROM AUTHOR]

We report the synthesis of a simple 1D Mn-azopyridine-based coordination polymer, poly-[MnII(NO3)2(OH2)2(azopy)2]·2MeCN (1) (azopy = 4,4′-azobis(pyridine)) and its use as a convenient feedstock to afford two 3D coordination polymers, namely: poly-[MnII(azopy)2(CNAgCN)4] (2), and poly-[MnII2(pda)(Hpda)2(azopy)2(OH2)2]·2MeCN (3), (pdaH2 = 1,4-phenylenediacetic acid). The compounds have been characterised by elemental analysis, IR, PXRD, TGA and single crystal X-ray diffraction. Compound 1 is a 1D coordination polymer while 2 represents a 3-dimensional coordination polymer adopting 2-fold interpenetrated rutile (rtl) topology and 3 is a 5-connected 3-dimensional coordination polymer with boron nitride (bnn) topology. [ABSTRACT FROM AUTHOR]

The reaction of MnCl2·4H2O with salicylaldoxime (H2salox) and the sodium salt of 1,3-bis(carboxypropyl)tetramethyldisiloxane (H2L) in a 1:1:1 molar ratio led to the self-assembly of {[Mn6O2(salox)6(H2salox)(H2O)3(μ-L)]H2salox·1.2H2O}n, a 1D coordination polymer consisting of hexamanganese(III) salicylaldoximate cluster as secondary building unit (SBU) and tetramethyldisiloxane-based dicarboxylate linker, namely, 1,3-bis(carboxypropyl)tetramethyldisiloxane. The structure of the compound was established by single crystal X-ray diffraction. The Mn(III) clusters consist of two staggered μ3-oxo-bridged Mn3 triangles held together by the oxygen atoms of the oxime groups. Because of Jahn-Teller distortion, the Mn-O distances reach 2.5 Å for the oxygen atoms located above and below the triangles mean planes. The compound showed a glass transition peak at around 14 °C in the differential scanning calorimetry (DSC) curve. The magnetic susceptibility data were fitted with a set of three intracluster antiferromagnetic exchange interaction coupling constants: J1 = −0.65 cm-1, J2 = −1.5 cm-1, and J3 = −0.9 cm-1. The ac magnetic susceptibility measurements in the 2-5 K temperature range reveal a frequency-dependent behavior indicative of a slow relaxation of magnetization at low temperature. The coexistence of the lypophilic 1,3-bis(propyl)tetramethyldisiloxane moieties and hydrophilic polar SBUs confers to the structure an amphiphilic character. Dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and transmission (TEM) and scanning (SEM) electron microscopies demonstrate that in dimethylformamide (DMF) the coordination polymer organizes as micelles, whereas in chloroform it tends to form inverse micelles and vesicles. [ABSTRACT FROM AUTHOR]

A rare 3-D Mn–organic framework, [(CH3)2NH2]3[Mn5(btc)4(Ac)(H2O)4]·5H2O (1), based on pentanuclear manganese clusters as building blocks has been prepared and structurally characterized by EA, IR, TGA, PXRD, and single-crystal X-ray diffraction. Structural analysis indicates the pentanuclear manganese cluster in1has a bow-like configuration, which is the first found to act as secondary building unit in the field of metal–organic framework. Gas adsorption measurements reveal that1can absorb a considerable amount of N2and CO2. [ABSTRACT FROM AUTHOR]

The reaction of Na2WO4 and Na2SeO3 in the presence of MnCl2 under moderately acidic conditions yielded two unprecedented tungstoselenites: dimeric K2Na10[K2⊂{MnSe4W23O85(H2O)6}]·29H2O (1) and trimeric wheel-shaped K2Na10[K2⊂{Mn3Se7W39O131(OH)20(H2O)2}]·60H2O (2). The assemblies of 1 and 2 are based upon the structure directing effects of SeIV heteroatoms for generating diverse well-defined vacancy selenotungstate precursors during the formation. The polyoxoanion of 1 contains two novel Wells-Dawson-type-like {Se2W11} fragments, which are constructed from novel {SeW4} and {SeW7} species derived from Wells-Dawson-type {α-Se2W14} fragments and one disorder of Mn/W center. The polyoxoanion of 2 exhibits a crown-type structure composed of a [Se6W38O120(OH)18(H2O)2]6- "host" (abbreviated as {Se6W38}) encapsulating SeO32--modified Mn/W and two K+ "guests". Remarkably, the crown {Se6W38} shell remains a new type of {Se2W12}-based trimeric aggregate in the polyoxometalates chemistry. The two compounds were characterized by single-crystal X-ray structure analysis, IR spectroscopy, thermogravimetric, UV/vis spectroscopy, and ESI-MS. Moreover, their photocatalytic H2 evolution activity was also investigated. [ABSTRACT FROM AUTHOR]

We investigate the structures and magnetic properties of boron-doped manganese clusters using first-principle density functional theory. We arrive at the lowest energy structures for clusters by simultaneously optimizing the cluster geometries, total spins, and relative orientations of individual atomic moments. For Mn n B ( n =2–12) clusters, the theoretical results indicate that the B atom prefers the surface site for all the lowest-energy structures except Mn 10 B cluster. The doped B atom enhances the stability of pure Mn n cluster. We also have studied the magnetic behavior of Mn–B clusters in the size range. Based on the analysis of the different magnetic behavior of boron-doped manganese clusters, we have further studied Mn 9 B 2 and Mn 8 B 3 clusters and it indicates that the doping of non-magnetism B element can induce all the Mn atoms align ferromagnetic coupling. Furthermore, a stable pearl necklace nanowire ([Mn 8 B 3 ] n → ∞ ) which retains the ferromagnetic ordering of all the manganese atoms has been predicted. [ABSTRACT FROM AUTHOR]

The employment of cyanato (OCN − ) group in high oxidation state manganese cluster chemistry, in conjunction with carboxylate ions and the organic chelating/bridging ligand 2-(hydroxymethyl)pyridine (hmpH), is reported. The syntheses, crystal structures, and magnetochemical characterization are described for [Mn 16 O 8 (OR) 4 (OCN) 4 (O 2 CMe) 12 (hmp) 6 (ROH) 2 ] (R = Me ( 1 ), Et ( 2 )) and [Mn 18 O 14 (O 2 CR) 18 (hmp) 4 (hmpH) 2 (H 2 O) 2 ] (R = Me ( 3 ), Et ( 4 )). The 2:1:1:1 reactions of Mn(O 2 CMe) 2 ·4H 2 O, hmpH, NaOCN and NEt 3 in solvent MeOH or EtOH afford the isostructural complexes [Mn 16 O 8 (OR) 4 (OCN) 4 (O 2 CMe) 12 (hmp) 6 (ROH) 2 ] (R = Me ( 1 ), Et ( 2 )). The [Mn 16 (μ 4 -O) 4 (μ 3 -O) 4 (μ-OMe) 4 (μ 3 -OR) 6 (μ-OR) 6 ] 10+ core of representative complex 1 comprises a Mn II 4 Mn III 4 double-cubane subunit attached on either side to two symmetry-related Mn II Mn III 3 defective dicubanes. A similar reaction of Mn(O 2 CR) 2 ·4H 2 O, hmpH, NaOCN and NEt 3 , but in solvent MeCN, led instead to the formation of [Mn 18 O 14 (O 2 CR) 18 (hmp) 4 (hmpH) 2 (H 2 O) 2 ] (R = Me ( 3 ), Et ( 4 )). Compounds 3 and 4 are very similar to each other and can be described as a central [Mn III 4 (μ-O) 6 ] rodlike subunit attached on either side to two symmetry-related [Mn 7 O 9 ] subunits. Variable-temperature, solid-state dc and ac magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions in all compounds, and possible S = 2 or 1 (for 1 and 2 ) and S = 0 (for 3 and 4 ) ground state spin values. The combined results demonstrate the ability of cyanato groups to facilitate the formation of new polynuclear Mn II/III complexes with structures different than these obtained from the use of the related azides. [ABSTRACT FROM AUTHOR]

The systematic exploration of the reactivity of [Mn(hfacac)2] with R-salicyloximes (R-saloxH2: R = H, Me, Et) yielded a family of clusters with nuclearities ranging from Mn4 to Mn12. The compounds with formula [Mn6(O)2(salox)6(CF3COO)2(EtOH)4] ( 1) and [Mn12(salox)12(O)4(N3)4(H2O)2(MeOH)6] ( 4) show two or four linked {Mn(µ3-O)(salox)3}+ triangular subunits. Magnetic measurements revealed spin ground states of S = 4 for 1 and S = 8 for 4, as well as single-molecule magnet responses and magnetic hysteresis above 2 K. The cubic [Mn4(Mesalox)4(MesaloxH)4] ( 2), the hexanuclear [Mn6(Etsalox)6(O)2(MeO)4(MeOH)2] ( 3) and the octanuclear [Mn8(Mesalox)6(O)2(N3)6(MeOH)8] ( 5) are polymorphs of previously reported systems. Small structural changes allows an S = 11 ground state for 3. [ABSTRACT FROM AUTHOR]

The systematic exploration of the reactivity of [Mn(hfacac)2] with R-salicyloximes (R-saloxH2: R = H, Me, Et) yielded a family of clusters with nuclearities ranging from Mn4 to Mn12. The compounds with formula [Mn6(O)2(salox)6(CF3COO)2(EtOH)4] ( 1) and [Mn12(salox)12(O)4(N3)4(H2O)2(MeOH)6] ( 4) show two or four linked {Mn(µ3-O)(salox)3}+ triangular subunits. Magnetic measurements revealed spin ground states of S = 4 for 1 and S = 8 for 4, as well as single-molecule magnet responses and magnetic hysteresis above 2 K. The cubic [Mn4(Mesalox)4(MesaloxH)4] ( 2), the hexanuclear [Mn6(Etsalox)6(O)2(MeO)4(MeOH)2] ( 3) and the octanuclear [Mn8(Mesalox)6(O)2(N3)6(MeOH)8] ( 5) are polymorphs of previously reported systems. Small structural changes allows an S = 11 ground state for 3. [ABSTRACT FROM AUTHOR]

Proton matrix ENDOR spectra were measured for Ca2+-depleted and Sr2+-substituted photosystem II (PSII) membrane samples from spinach and core complexes from Thermosynechococcus vulcanus in the S2 state. The ENDOR spectra obtained were similar for untreated PSII from T. vulcanus and spinach, as well as for Ca2+-containing and Sr2+-substituted PSII, indicating that the proton arrangements around the manganese cluster in cyanobacterial and higher plant PSII and Ca2+-containing and Sr2+-substituted PSII are similar in the S2 state, in agreement with the similarity of the crystal structure of both Ca2+-containing and Sr2+-substituted PSII in the S1 state. Nevertheless, slightly different hyperfine separations were found between Ca2+-containing and Sr2+-substituted PSII because of modifications of the water protons ligating to the Sr2+ ion. Importantly, Ca2+ depletion caused the loss of ENDOR signals with a 1.36-MHz separation because of the loss of the water proton W4 connecting Ca2+ and YZ directly. With respect to the crystal structure and the functions of Ca2+ in oxygen evolution, it was concluded that the roles of Ca2+ and Sr2+ involve the maintenance of the hydrogen bond network near the Ca2+ site and electron transfer pathway to the manganese cluster. [ABSTRACT FROM AUTHOR]

Temperature-programmeddesorption (TPD) experiments were performedon gas-phase manganese oxide cluster ions, namely, MnnOm+(n= 3–20) and MnnOm–(n=3–18). These cluster ions were prepared by laser ablation ofa manganese rod in the presence of oxygen gas, and their compositionwas investigated using mass spectrometry. The composition of MnnOm±distribution lies above the m= (4/3)nline. When the cluster ions were heated to 1000 K, MnnOm+(m= (4/3)n+ δ, with δ = −1,0) and MnnOm–(m= (4/3)n+ δ, with δ = 0, 1) was found to be the predominantspecies, formed by thermal dissociation. These experimental findingsindicate that the nascent manganese oxide clusters comprise robustMnnOm±(m/n≈ 4/3)and weakly bound excess oxygen atoms. On the basis of the TPD experiments,the oxygen-molecule release was identified as the main dissociationchannel. The temperature dependence of O2desorption wasfound to be similar among the clusters with the same oxygen excessor deficiency regardless of the number of Mn atoms. The thresholdenergy of O2desorption was estimated for Mn4Om+(m=6–11) and compared with bond dissociation energies calculatedby density functional theory. [ABSTRACT FROM AUTHOR]

A new Mn16 topology consisting of one hexanuclear {MnII2MnIII4} unit coordinated inside a decametallic {MnII6MnIII2MnIV2} wheel was synthesized from 2-pyridylcyanoxime and azido ligands. A new tetrazole-2-pyridylketoneoximate ligand was obtained in situ by cyclization of the cyano group and azide mediated by manganese cations. [ABSTRACT FROM AUTHOR]

The article presents abstracts on inorganic chemistry topics which include manganese clusters, photoactive porous silicon, and rare-earth imido complexes.

Photosystem II (PSII) catalyzes the light-induced generation of oxygen from water. The oxygen-evolving complex is buried deep in the protein on the lumenal side of PSII, and water molecules need to pass through protein subunits to reach the active site-the manganese cluster. Previous studies on the elucidation of water channels in PSII were based on an analysis of the cavities in the static PSII structure determined by X-ray diffraction. In the present study, we perform molecular dynamics simulations of the water movement in the transport system of PSII. [ABSTRACT FROM AUTHOR]

The PsbP protein is an extrinsic subunit of photosystem II (PSII) that is essential for photoautotrophic growth in higher plants. Several crystal structures of PsbP have been reported, but the binding topology of PsbP in PSII has not yet been clarified. In this study, we report that the basic pocket of PsbP, which consists of conserved Arg48, Lys143, and Lys160, is important for the electrostatic interaction with the PSII complex. Our release-reconstitution experiment showed that the binding affinities of PsbP-R48A, -K143A, and -K160A mutated proteins to PSII were lower than that of PsbP-WT, and triple mutations of these residues greatly diminished the binding affinity to PSII. Even when maximum possible binding had occurred, the R48A, K143A, and K160A proteins showed a reduced ability to restore the rate of oxygen evolution at low chloride concentrations. Fourier transform infrared resonance (FTIR) difference spectroscopy results were consistent with the above finding, and suggested that these mutated proteins were not able to induce the normal conformational change around the Mn cluster during S1 to S2 transition. Finally, chemical cross-linking experiments suggested that the interaction between the N-terminus of PsbP with PsbE was inhibited by these mutations. These data suggest that the basic pocket of PsbP is important for proper association and interaction with PSII. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy. [ABSTRACT FROM AUTHOR]

Photosystem II (PSII) is a membrane-bound protein complex that oxidizes water to produce energized protons, which are used to built up a proton gradient across the thylakoidal membrane in the leafs of plants. This light-driven reaction is catalyzed by withdrawing electrons from the Mn4CaO5-cluster (Mn-cluster) in four discrete oxidation steps [S1 - (S4 / S0)] characterized in the Kok-cycle. In order to understand in detail the proton release events and the subsequent translocation of such energized protons, the protonation pattern of the Mn-cluster need to be elucidated. The new high-resolution PSII crystal structure from Umena, Kawakami, Shen, and Kamiya is an excellent basis to make progress in solving this problem. Following our previous work on oxidation and protonation states of the Mn-cluster, in this work, quantum chemical/electrostatic calculations were performed in order to estimate the pKa of different protons of relevant groups and atoms of the Mn-cluster such as W2, O4, O5 and His337. In broad agreement with previous experimental and theoretical work, our data suggest that W2 and His337 are likely to be in hydroxyl and neutral form, respectively, O5 and O4 to be unprotonated. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy. [ABSTRACT FROM AUTHOR]

Two molecular grid-like clusters are reported, one is a discrete [3 x 5] grid and the other a [3 x 4] grid within a Mn12Ni2 loop. Both Mn24Ni2 and Mn15 aggregates display novel and aesthetically pleasing structures with the former one being among the highest nuclearity heterometallic MnxMy clusters (M = any transition metal ion). [ABSTRACT FROM AUTHOR]

Abstract: Photosystem II (PSII) is a membrane-bound protein complex that oxidizes water to produce energized protons, which are used to built up a proton gradient across the thylakoidal membrane in the leafs of plants. This light-driven reaction is catalyzed by withdrawing electrons from the Mn4CaO5-cluster (Mn-cluster) in four discrete oxidation steps [S1 −(S4 /S0)] characterized in the Kok-cycle. In order to understand in detail the proton release events and the subsequent translocation of such energized protons, the protonation pattern of the Mn-cluster need to be elucidated. The new high-resolution PSII crystal structure from Umena, Kawakami, Shen, and Kamiya is an excellent basis to make progress in solving this problem. Following our previous work on oxidation and protonation states of the Mn-cluster, in this work, quantum chemical/electrostatic calculations were performed in order to estimate the pKa of different protons of relevant groups and atoms of the Mn-cluster such as W2, O4, O5 and His337. In broad agreement with previous experimental and theoretical work, our data suggest that W2 and His337 are likely to be in hydroxyl and neutral form, respectively, O5 and O4 to be unprotonated. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy. [Copyright &y& Elsevier]

The syntheses, structures, and magnetic properties are reported for three new Ce/Mn clusters with different Ce/Mn ratios: [Ce6Mn4O12(O2CMe)10(NO3)4(py)4] (py = pyridine) (1), [CeMngOg(O2CCH2tBu)12(DMF)14] (DMF = dimethylformamide) (2), and [Ce2Mn4O2(O2CMe)6(NO3)4(hmp)4] (3; hmp- is the anion of 2-(hydroxymethyl)pyridine). 1 and 2 were obtained from the reaction of CeIV with [Mn12O12(O2CMe)16(H2O)4] (MnIII8Mn(IV)4) and [MngO2(O2CCH2tBu)14tBuCH2CO2H)4] (MnII6MnIII2), respectively, whereas 3 resulted from the oxidation of MnII acetate with CeIV in the presence of hmpH. Cluster 1 possesses an unusual [Ce6Mn4O12]14+ core topology consisting of a [Ce6O8] face-capped octahedron, which is face-fused at each end to a [CeIV2MnIIIMnIVO4] cubane. Cluster 2 possesses a nonplanar, saddlelike loop of eight MnIII atoms bridged by eight µ3-O2- ions to a central CeIV atom. Cluster 3 is similar to 1 in possessing an octahedral core, but this is now a [Ce2Mn4] octahedron consisting of a CeIII atom on either side of a Mn4 parallelogram, with the metal atoms bridged by two µ4-O2- ions, the alkoxide arms of four hmp- groups, and six acetates. Clusters 1, 2, and 3 are thus at the CeIV6MnIII2MnIV2, CeIVMnIII8, and CeIII2MnIII4 oxidation levels, respectively. Variable-temperature, solid-state direct current (DC) and alternating current (AC) magnetization studies on 1-3 in the 5.0-300 K range revealed predominantly antiferromagnetic exchange interactions within the complexes. For 1, fitting of the DC data to the theoretical expression for a dinuclear MnIIIMnIV complex derived using the Van Vleck equation and an isotropic spin Hamiltonian (x = -2JŜi·Sj convention) gave a value for the exchange coupling parameter (J) of -60.4(7) cm-1 and a Landé factor g = 2.00(1), indicating an S = 1/2 ground state. For 2, both DC and AC data indicate an S = 0 ground state, which is unprecedented for a member of the CeMng family and now means members of the latter have been made that span the whole range of possible ground states from S = 0 to the maximum S = 16. Cluster 3 possesses an S = 0 ground state for its Mn4 fragment, with the paramagnetism remaining at low temperature coming from the weakly coupled Ce(III) centers. These three species are new additions to the Mn-Ce family of clusters and the broader class of 3d/4f molecular systems. [ABSTRACT FROM AUTHOR]

Oxidation of some manganese complexescontaining both carboxylateand water/hydroxo ligands does not result in changes to the carboxylatestretching frequencies. The water oxidizing complex of photosystemII is one motivating example. On the basis of electronic structuretheory calculations, we here suggest that the deprotonation of wateror hydroxo ligands minimizes changes in the vibrational frequenciesof coligating carboxylates, rendering the carboxylate modes “invisible”in FTIR difference spectroscopy. This deprotonation of water/hydroxoligands was also found to balance the redox potentials of the Mn(II)/Mn(III)and Mn(III)/Mn(IV) couples, allowing the possibility for successivemanganese oxidations at a relatively constant redox potential. [ABSTRACT FROM AUTHOR]

Highlights: [•] The lowest-energy structures of the Ni n Mn (n =1–12) clusters are obtained using all-electron DFT-GGA calculations. [•] The magnetic moments are enhanced on substituting one Ni atom by one Mn atom in the Ni n+1 (n =1–9, 11 and 12) clusters. [•] The Ni3Mn, Ni5Mn, Ni8Mn and Ni10Mn clusters are found to be more stable than their neighbors. [•] The magnetic moment surface enhancement effect can be demonstrated from the magnetic properties of the doped Mn atom. [Copyright &y& Elsevier]

Abstract: The combination of azide, carboxylate (pivalate and in situ generated formate) and triethanolamine ligands in higher oxidation state Mn cluster chemistry has afforded a new pentadecanuclear, mixed-valence(II,III) compound with a large S and a negative D value. The unprecedented [MnII 2MnIII 13] cluster exhibits frequency-dependent out-of-phase (χ M″) signals, characteristics of the superparamagnetic-like slow relaxation of an SMM. [Copyright &y& Elsevier]

The reaction of MnBr2·4H2O with 2-(hydroxymethyl)-2-((3-hydroxynaphthalen-2-yl)methyleneamino)propane-1,3-diol (LH4) in MeOH, afforded the complex [MnIV(LH2)2]·MeOH (1·MeOH) in very good yield. Repeating the same reaction and replacing MnBr2 4H2O with Mn(OAc)2·4H2O gave the complex [MnIII 2MnII(LH2)2(OAc)4(MeOH)2]·4MeOH (2·4MeOH) in good yield. Finally, the reaction of Mn(OAc)2·4H2O, with LH4 and PhCOONa in the presence of NEt3 in MeOH, afforded the complex [MnIII 2MnII(LH2)2(OAc)2(O2CPh)2(MeOH)2]·MeOH (3·MeOH) in moderate yield. The crystal structures of 1–3 have been determined by single-crystal X-ray crystallography. Complex 1 is a mononuclear MnIV complex, in which the metal ion is found in a trans-O4N2 octahedral environment. Complex 2 is a mixed-valent linear [MnIII 2MnII] cluster in which the central MnII ion is connected via carboxylates and monoatomic bridges from the tetraol ligands to the two terminal MnIII ions, while cluster 3 can be regarded as the “incomplete” benzoate analogue of complex 2. DC magnetic susceptibility studies were performed on a polycrystalline samples of 2 and 3, revealing the presence of antiferromagnetic interactions within the clusters leading to an S =1/2 ground-state for both complexes. [ABSTRACT FROM AUTHOR]

Series of manganese clusters derived from 2-pyridylcyanoxime with Mn3II (1), Mn4II (2a, b), MnII4MnIII4 (3), MnII2MnIII6MnIV2 (4) and MnII3MnIII6MnIV (5) cores have been characterized. Dc magnetic measurements reveal antiferromagnetic coupling for 1–4 and dominant ferromagnetic interactions for 5 which shows the largest ground state reported to date in pyridyloximate chemistry (S = 14). [ABSTRACT FROM AUTHOR]

Rechargeable molecular-cluster batteries (MCBs) based on the manganese cluster complex [Mn12O12(CH3CH2C(CH3)2COO)16(H2O)4] ([Mn12]) that exhibited a capacity of approximately 200 A h kg−1 in the battery voltage range of 4.0 to 2.0 V were developed. In these batteries, the capacity of approximately 100 A h kg−1 in the range of 4.0-3.0 V is caused by a chemical reduction from [Mn12]0 to [Mn12]8−, whereas the other half in the range of 3.0-2.0 V cannot be explained by a redox change of the Mn ions. We performed the cyclic voltammetry (CV) and 7Li solid-state NMR measurements on the Mn12-MCBs to investigate the origin of the capacity below 3.0 V. Pseudo-rectangular-shaped CV curves in the range of 3.0-2.0 V demonstrate the presence of an electrical double-layer (EDL) capacitance in Mn12-MCBs, which corresponds to approximately 100 A h kg−1. 7Li NMR studies suggest that Li ions form an EDL with electrons in carbon black electrodes in the capacitance voltage range. The capacitance effects are not formed by the single-carbon electrodes alone, but appear only in the mixture of Mn12 and the carbon black electrodes. This type of coexistence of capacitance effects and redox reaction in one electrochemical cell is quite unusual and can serve as a new working principle for high-performance energy-storage devices. [ABSTRACT FROM AUTHOR]

The solar water-splitting protein complex, photosystem II, catalyzes one of the most energetically demanding reactions in Nature by using light energy to drive the catalytic oxidation of water. Photosystem II contains two symmetrically placed tyrosine residues, YD and YZ, one on each subunit of the heterodimeric core. The YZ residue is kinetically competent and is proposed to be directly involved in the proton-coupled electron transfer reactions of water oxidation. In contrast, the YD proton-coupled electron transfer redox poises the catalytic tetranuclear manganese cluster and may electrostatically tune the adjacent monomeric redox-active chlorophyll and β-carotene in the secondary electron transfer pathway of photosystem II. In this study, we apply pulsed high-frequency electron paramagnetic resonance (EPR) and electron nuclear double-resonance (ENDOR) spectroscopy to study the photochemical proton-coupled electron transfer (PCET) intermediates of YD. We detect the "unrelaxed" and "relaxed" photoinduced PCET intermediates of YD using high-frequency EPR spectroscopy and observe an increase of the g anisotropy upon temperature-induced relaxation of the unrelaxed intermediate to the relaxed state as previously observed by Faller et al. [(2002) Biochemistry 41, 12914-12920; (2003) Proc. Natl. Acad. Sci. U.S.A. 100, 8732-8735]. This observation suggests the presence of structural differences between the two intermediates. We probe the possible structural differences by performing high-frequency 2H ENDOR spectroscopy experiments. On the basis of numerical simulations of the experimental 2H ENDOR spectra, we confirm that (i) there is a significant change in the H-bond length of the tyrosyl radical in the unrelaxed (1.49 Å) and relaxed (1.75 Å) PCET intermediates. This observation suggests that the D2-His189 residue is deprotonated prior to electron transfer at the YD residue and (ii) there are negligible changes in the conformation of the tyrosyl ring in the unrelaxed and relaxed PCET intermediates of YD. [ABSTRACT FROM AUTHOR]

Highlights: [•] B3LYP, CASPT2 and RCCSD(T) geometry optimizations for carried out. [•] Ground states and spectroscopic relevant excited states determined. [•] CASPT2 and RCCSD(T) adiabatic and vertical detachment energies calculated. [•] Assignment for anion photoelectron spectra proposed. [•] Multidimensional Franck–Condon simulations given. [Copyright &y& Elsevier]

Understanding the effect of redox-inactive metals on the properties of biological and heterogeneous water oxidation catalysts is important both fundamentally and for improvement of future catalyst designs. In this work, heterometallic manganese-oxido cubane clusters [MMn3O4] (M = Sr2+, Zn2+, Sc3+, Y3+] structurally relevant to the oxygen-evolving complex (OEC) of photosystem II were prepared and characterized. The reduction potentials of these clusters and other related mixed metal manganese-tetraoxido complexes are correlated with the Lewis acidity of the apical redox-inactive metal in a manner similar to a related series of heterometallic manganese-dioxido clusters. The redox potentials of the [SrMn3O4] and [CaMn3O4] clusters are close, which is consistent with the observation that the OEC is functional only with one of these two metals. Considering our previous studies of [MMn3O2] moieties, the present results with more structurally accurate models of the OEC ([MMn3O4]) suggest a general relationship between the reduction potentials of heterometallic oxido clusters and the Lewis acidities of incorporated cations that applies to diverse structural motifs. These findings support proposals that one function of calcium in the OEC is to modulate the reduction potential of the cluster to allow electron transfer. [ABSTRACT FROM AUTHOR]

For the sake of producing a giant magnetic moment in small manganese clusters, we have performed a density function theory calculation on MnNPd (N= 1–5) clusters. The results demonstrate that the doped -Pd atoms do not alter the basic framework, but significantly improve the average binding energy of host Mn clusters. The interaction among Mn atoms for MnNPd becomes weaker in comparison with corresponding MnNclusters which plays an important role in the appearance of giant magnetic moments of the system. Mn4Pd is the most promising in terms of gaining substantial binding energy as well as achieving larger ferromagnetic alignment (20μB). [ABSTRACT FROM AUTHOR]

The photosystem II reaction center mediates the light-induced transfer of electrons from water to plastoquinone, with concomitant production of O2. Water oxidation chemistry occurs in the oxygen-evolving complex (OEC), which consists of an inorganic Mn4CaO5 cluster and its surrounding protein matrix. Light-induced Fourier transform infrared (FTIR) difference spectroscopy has been successfully used to study the molecular mechanism of photosynthetic water oxidation. This powerful technique has enabled the characterization of the dynamic structural changes in active water molecules, the Mn4CaO5 cluster, and its surrounding protein matrix during the catalytic cycle. This mini-review presents an overview of recent important progress in FTIR studies of the OEC and implications for revealing the molecular mechanism of photosynthetic water oxidation. [ABSTRACT FROM AUTHOR]

Abstract: The 1D coordination polymer [MnIII 6O2(O2CC6H4CO2)(salox)6(dmf)4] n ·2n(dmf) (2·2n(dmf)) was obtained from the reaction of [MnIII 6O2(O2CPh)2(salox)6(Me2CO)2(H2O)2]·2Me2CO (1·2Me2CO) with excess of terephthalic acid in MeCN/dmf. The structure of 2 consists of [MnIII 6O2(salox)6(dmf)4]2+ units bridged through the terephthalato dianions. The Mn6 units present the [Mn6(μ 3-O)2(μ 2-OR)2]12+ core and can be described as two [Mn3(μ 3-O)]7+ triangular subunits linked by two μ2-oximato oxygen atoms of the salox2− ligands, which show the μ3-κ2 O:κO′:κN coordination mode. Each carboxylato group of the terephthalato dianion is coordinated through the usual syn,syn μ2-κO:κO′ coordination mode. Both 2 and 1 contain the same [Mn6(μ 3-O)2(μ 2-OR)2]12+ core, and the replacement of the two benzoates in 1 from the terephthalato dianion generates the 1D structure in 2. The dynamic magnetic properties of both compounds were monitored by alternating current magnetic susceptibility measurements. Both complexes exhibit Single Molecule Magnet behavior with no evidence for inter-cluster magnetic interactions for 2. For complex 1 an unusually broad distribution of relaxation times was observed. [Copyright &y& Elsevier]

Abstract: Three manganese clusters have been synthesised via the reaction of MnII with cyano(imino(methoxy)methyl)nitrosomethanide (cmnm), obtained from the in situ nucleophilic addition of MeOH to dicyanonitrosomethanide (dcnm). X-ray crystallographic studies show that the complex [MnII 3(cmnm)6]·MeOH (1) is a linear trinuclear species, with a central octahedral and two outer trigonal-prismatic manganese(II) ions. Two mixed-valent tetranuclear complexes [MnII 2MnIII 2O2(cmnm)4Cl2(MeOH)6] (2) and [MnII 2MnIII 2O2(cmnm)4Cl2(MeOH)4(pzH)2]·2MeOH (3) (pzH=pyrazole) contain two MnII and two MnIII ions in butterfly-type structures, with the six-coordinate ‘body’ MnIII ions bridged to the seven-coordinate ‘wingtip’ MnII ions by μ3-O2− and by nitroso oxygen atoms of the cmnm ligands. The formation of the trinuclear and tetranuclear manganese clusters is dependent on the stoichiometry used in the reactions. Solid state DC magnetic susceptibility studies on complexes 1 and 3 reveal that antiferromagnetic interactions are dominant within the clusters. Fits of the data reveal an S = 5/2 ground state for 1 and a S =0 ground state for 3, with several close lying excited states found in both cases. [Copyright &y& Elsevier]

A class I ribonucleotide reductase (RNR) uses either a tyrosyl radical (Y•) or a Mn

A new Mn(II) complex formulated as [Mn(bpy)(HO)][Mn(bpy)(pdtc)]·14HO ( 1) (where Hpdtc=pyridine-2,3,5,6-tetracarboxylic acid, bpy=2,2′-bipyridine) has been prepared and characterized by IR spectroscopy, elemental analysis and single crystal X-ray diffraction. Complex 1 is tetranuclear and composed of a [Mn(bpy)(pdtc)] anion and two [Mn(bpy)(HO)] cations. The particular interest of complex 1 is the formation of a centrosymmetric water cluster (HO) included a chair-shaped hexamer and two trimer clusters. The tetra-nuclear units are further aggregated by hydrogen bonding with (HO) clusters and π···π stacking interactions to form a 3D supramolecular architecture. Graphical Abstract: A new Mn(II) complex with pyridine-2,3,5,6-tetracarboxylic acid features a tetra-nuclear unit and a centrosymmetric water cluster (HO). The 3D supramolecular architecture are further aggregated by hydrogen bonding with (HO) clusters and π···π stacking interactions.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The synthesis of reduced coordination (less than 6), unchelated manganese oxygen cluster systems is described. Addition of phenols to Mn(NR2)2 (R = SiMe3) results in protolytic amide ligand replacement, and represents the primary entry into the described chemistry. Addition of PhOH to Mn(NR2)2 results in the formation of the heteroleptic dimer Mn2(μ-OPh)2(NR2)2(THF)2 (1). Usage of the sterically larger 2,6-diphenylphenol (Ph2C2H3OH) as the ligand source results in the formation of a 3-coordinate heteroleptic dimer without THF coordination, Mn2(μ-OC6H3Ph2)2(NR2)2 (2). Attempts to generate 2 in the presence of THF or Et2O resulted in isolation of monomelic Mn(OC6H3Ph2)2L2 (3, L = THF, Et2O). Use of the .sterically intermediate 2,4,6-trimethylphenol (MesOH) resulted in formation of the linear trinuclear cluster Mn3(μ-OMes)4(NR2)2(THF)2 (4). Reaction of Mn(NR2)2 with PhOH in the presence of water, or reaction of 1 with water, results in the formation of a 5-coordinate, unchelated Mn--O cluster, Mn8(μs-O)2(μ-OPh)12(THF)6 (5). Preparation, structures, steric properties, and magnetic properties are presented. Notably, complex 5 exhibits a temperature-dependent phase transition between a 4-spin paramagnetic system at low temperature, and an 8-spin paramagnetic system at room temperature. [ABSTRACT FROM AUTHOR]