Synthesis, crystal structure and electrochemical behavior of tetranuclear transition metal clusters based on lacunary silicotungstates: [M4(H2O)2(SiW9O34)2]10− (M = Ni2+, Co2 +) and [Fe4(μ-O)2(μ-OH)2(SiW10O37)2]14−

Three tetranuclear transition metal clusters based on lacunary silicotungstates [M₄(H₂O)₂(SiW₉O₃₄)₂]^12? (M = Ni²⁺ (1), Co²⁺ (2)), and [Fe₄(μ-O)₂(μ-OH)₂(SiW₁₀O₃₇)₂]^14? (3) have been synthesized under ambient conditions and characterized by elemental analyses, IR, TG, cyclic voltammetry, and single-crystal X-ray diffraction. The polyoxoanions of 1 and 2 are isostructural, including a central rhomb-like {M₄O₁₆} (M = Ni, Co) cluster sandwiched by two trivacant {B-α-SiW₉} Keggin moieties. In the polyoxoanion of 3, two μ-OH and two μ-O bridges link with four Fe^III ions, forming an eight-membered ring. This [Fe₄(μ-OH)₂(μ-O)₂] aggregation is sandwiched by two bi-vacant {α-SiW₁₀} Keggin fragments. The electrochemical properties of the three compounds were investigated.     

The First 3‐Connected SrSi2‐Type 3D Chiral Framework Constructed from {Ni6PW9} Building Units

A novel 3‐connected SrSi₂‐type 3D chiral framework constructed from hexa‐Ni^II‐cluster‐substituted polyoxometalate (POM) units [Ni(enMe)₂]₃[WO₄]₃[Ni₆(enMe)₃(OH)₃PW₉O₃₄]₂?9H₂O ( 1 ) (enMe=1,2‐diaminopropane) has been made from a hydrothermal synthetic method. This POM represents the first 3D framework based on {Ni₆PW₉} units and {WO₄} connectors.     

Two new transition metal inorganic–organic hybrid borates: [tris(2‐aminoethoxy)trihydroxyhexaborato]cobalt(II) and its nickel(II) analogue

The two isomorphous title compounds, [1,5,9‐tris(2‐aminoethoxy)‐3,7,11‐trihydroxy‐3,7,11‐tribora‐1,5,9‐triborata‐2,4,6,8,10,12‐hexaoxa‐13‐oxoniatricyclo[7.3.1.0^5,13]tridecane]cobalt(II), [Co(C₆H₂₁B₆N₃O₁₃)] or Co{B₆O₇(OH)₃[O(CH₂)₂NH₂]₃}, and the Ni^II analogue, [Ni(C₆H₂₁B₆N₃O₁₃)], each consist of an M^II cation and an inorganic–organic hybrid {B₆O₇(OH)₃[O(CH₂)₂NH₂]₃}²⁻ anion. The M^II cation lies on a crystallographic threefold axis (as does one O atom) and is octahedrally coordinated by three N atoms from the organic component. Three O atoms covalently link the B–O cluster and the organic component. Molecules are connected to one another through N—H...O and O—H...O hydrogen bonds, forming a three‐dimensional supramolecular network.     

Binary salt of a palladium(II) complex with (phosphonomethyl)phosphonic (medronic) acid comprising `handbell‐like' [Pd{μ‐CH2(PO3)2}]3 units

The asymmetric unit of the title compound, dipotassium bis[hexaaquanickel(II)] tris(μ₂‐methylenediphosphonato)tripalladium(II) hexahydrate, K₂[Ni(H₂O)₆]₂[Pd₃{CH₂(PO₃)₂}₃]·6H₂O, consists of half a {[Pd{CH₂(PO₃)₂}]₃}⁶⁻ anion [one Pd atom (4e) and a methylene C atom (4e) occupy positions on a twofold axis] in a rare `handbell‐like' arrangement, with K⁺ and [Ni(H₂O)₆]²⁺ cations to form the neutral complex, completed by three solvent water molecules. The {[Pd{CH₂(PO₃)₂}]₃}⁶⁻ units exhibit close Pd...Pd separations of 3.0469 (4) Å and are packed via intermolecular C—H...Pd hydrogen bonds. The [KO₉] and [NiO₆] units are assembled into sheets coplanar with (011) and stacked along the [100] direction. Within these sheets there are [K₄Ni₄O₈] and [K₂Ni₂O₄] loops. Successive alternation of the sheets and [Pd{CH₂(PO₃)₂}]₃ units parallel to [001] produces the three‐dimensional packing, which is also supported by a dense network of hydrogen bonds involving the solvent water molecules.     

Heterotrimetallic Coordination Polymers: {CuIILnIIIFeIII} Chains and {NiIILnIIIFeIII} Layers: Synthesis,Crystal Structures,and Magnetic Properties

The use of the [Fe^III(AA)(CN)₄]^? complex anion as metalloligand towards the preformed [Cu^II(valpn)Ln^III]³⁺ or [Ni^II(valpn)Ln^III]³⁺ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and 1,10‐phenathroline (phen); H₂valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {[Cu^II(valpn)Ln^III(H₂O)₃(μ‐NC)₂Fe^III(phen)(CN)₂ {(μ‐NC)Fe^III(phen)(CN)₃}]NO₃ ? 7 H₂O}_n (Ln=Gd ( 1 ), Tb ( 2 ), and Dy ( 3 )) and the trinuclear complex [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃] ? NO₃ ? H₂O ? CH₃CN ( 4 ) were obtained with the [Cu^II(valpn)Ln^III]³⁺ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[Ni^II(valpn)Ln^III(ONO₂)₂(H₂O)(μ‐NC)₃Fe^III(bipy)(CN)] ? 2 H₂O ? 2 CH₃CN}_n (Ln=Gd ( 5 ), Tb ( 6 ), and Dy ( 7 )) resulted with the related [Ni^II(valpn)Ln^III]³⁺ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃]⁺, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {Fe^III(bipy)(CN)₄} moiety in 5 – 7 acts as a tris‐monodentate ligand towards three {Ni^II(valpn)Ln^III} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the Cu^II?Ln^III ( 1 – 3 ) and Ni^II?Ln^III ( 5 – 7 ) units, as well as through the single cyanide bridge between the Fe^III and either Ni^II ( 5 – 7 ) or Cu^II ( 4 ) account for the overall ferromagnetic behavior observed in 1 – 7 . DFT‐type calculations were performed to substantiate the magnetic interactions in 1 , 4 , and 5 . Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τ_o) and energy barrier (E_a) through the Arrhenius equation being 2.0×10^?12 s and 29.1 cm^?1, respectively. In the case of 7 , the ferromagnetic interactions through the double phenoxo (Ni^II–Dy^III) and single cyanide (Fe^III–Ni^II) pathways are masked by the depopulation of the Stark levels of the Dy^III ion, this feature most likely accounting for the continuous decrease of χ_M T upon cooling observed for this last compound.     

A charge-separation-type ionic solid composed of hexanuclear complexes with a macrocyclic tetragold(I) metalloligand

The reaction of Na[Co^III(d -ebp)] (d -H₄ebp = N,N′-ethylenebis[d -penicillamine]) with [(Au^ICl)₂(dppe)] (dppe = 1,2-bis[diphenylphosphino]ethane) gave a cationic Au^I₄Co^III₂ hexanuclear complex, [Co^III₂(L^Au4)]²⁺ ([ 1 ]²⁺), where [L^Au4]⁴⁻ is a cyclic tetragold(I) metalloligand with a 32-membered ring, [Au^I₄(dppe)₂(d -ebp)₂]⁴⁻. Complex [ 1 ]²⁺ crystallized with NO₃⁻ to produce a charge-separation (CS)-type ionic solid of [ 1 ](NO₃)₂. In [ 1 ](NO₃)₂, the complex cations are assembled to form cationic supramolecular hexamers of {[ 1 ]²⁺}₆, which are closely packed in a face-centered cubic (fcc) lattice structure. The nitrate anions of [ 1 ](NO₃)₂ were accommodated in hydrophilic and hydrophobic tetrahedral interstices of the fcc structure to form tetrameric and hexameric nitrate clusters of {NO₃⁻}₄ and {NO₃⁻}₆, respectively. An analogous CS-type ionic solid formulated as [Ni^IICo^III(L^Au4)](NO₃) ([ 2 ](NO₃)) was obtained when a 1:1 mixture of Na[Co^III(d -ebp)] and [Ni^II(d -H₂ebp)] was reacted with [(Au^ICl)₂(dppe)], accompanied by the conversion of the diamagnetic, square-planar [Ni^II(d -H₂ebp)] to the paramagnetic, octahedral [Ni^II(d -ebp)]²⁻. While the overall fcc structure in [ 2 ](NO₃) was similar to that of [ 1 ](NO₃)₂, none of the nitrate anions were accommodated in any hydrophobic tetrahedral interstice, reflecting the difference in the complex charges between [ 1 ]²⁺ and [ 2 ]⁺.     

FeIII48-Containing 96-Tungsto-16-Phosphate: Synthesis,Structure, Magnetism and Electrochemistry

The 48-Fe^III-containing 96-tungsto-16-phosphate, [Fe^III₄₈(OH)₇₆(H₂O)₁₆(HP₂W₁₂O₄₈)₈]³⁶⁻ ( Fe₄₈ ), has been synthesized and structurally characterized. This polyanion comprises eight equivalent {Fe^III₆P₂W₁₂} units that are linked in an end-on fashion forming a macrocyclic assembly that contains more iron centers than any other polyoxometalate (POM) known to date. The novel Fe₄₈ was synthesized by a simple one-pot reaction of an {Fe₂₂} coordination complex with the hexalacunary {P₂W₁₂} POM precursor in water. The title polyanion was characterized by single-crystal XRD, FTIR, TGA, magnetic and electrochemical studies.     

A {Co4O4} Cubane Incorporated within a Polyoxoniobate Cluster

A novel octacobalt‐containing polyoxoniobate, Na₆K₁₂[H₂Co₈O₄(Nb₆O₁₉)₄]?39 H₂O, has been prepared by a combination of hydrothermal and diffusion methods. The polyanion [H₂Co₈O₄(Nb₆O₁₉)₄]^18? incorporates a tetrameric assembly of Lindqvist‐type [Nb₆O₁₉]^8? fragments trapping a {Co^II₄Co^III₄} cluster which comprises a central {Co^III₄O₄} cubane core, surrounded by another four Co^II ions linkers. Furthermore, magnetic measurements show that the compound exhibits antiferromagnetic interactions.     

Ferromagnetic NiII Discs

A family of planar disc‐like hexa‐, octa‐ and decametallic Ni^II complexes exhibit dominant ferromagnetic exchange. The deca‐ and octametallic clusters [Ni^II₁₀(tmp)₂(N₃)₈(acac)₆(MeOH)₆] ( 1 , H₃tmp=1,1,1‐tris(hydroxymethyl)propane; acac=acetylacetonate) and [Ni^II₈(thme)₂(O₂CPh)₄(Cl)₆(MeCN)₆(H₂O)₂] ( 2 , H₃thme=1,1,1‐tris(hydroxymethyl)ethane) represent rare examples of Ni^II‐based single‐molecule magnets, and [Ni^II₁₀] ( 1 ) possesses the largest barrier to magnetisation reversal of any Ni^II single‐molecule magnet to date.     

A series of new organic–inorganic compounds templated by the [SiW12O40]4− polyanion

Two couples of new compounds templated by the polyanion [SiW₁₂O₄₀]^4?,[Hbix][Cu^I(bix)]₃[SiW₁₂O₄₀]·4H₂O (1) and [Cu^II(H₂O)(Hbix)₂(bix)]₂[Cu^II(H₂O)₂(Hbix)₂(bix)][SiW₁₂O₄₀]₃·4H₂O (2) (bix = 1,4-Bis(imidazol-1-ylmethyl)benzene), [Cu^I(bbi)]₄[SiW₁₂O₄₀]·2H₂O (3) and [Cu^II(bbi₂)]₂[SiW₁₂O₄₀] (4) (bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) were hydrothermally synthesized, and characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses and single X-ray diffraction. Compounds 1 and 2 were synthesized from the same reactants but exhibited distinct structures which could be ascribed to the different ratios of the reactant bix to Cu^II. In compound 1, the higher ratio of bix results in the transformation of the Cu^II to Cu^I, the [SiW₁₂O₄₀]^4? templates direct the Cu^I–bix coordination polymers to form a 3D supramolecular framework with grid-like channels along two directions. The [SiW₁₂O₄₀]^4? templates in compound 2 locate in the voids of the 3D supramolecular network constructed by Cu^II–bix coordination polymers, which exhibits the interdigitation fashion in both the formation of the 2D layer and the 3D framework. Compounds 3 and 4 were synthesized similar to 1 and 2, except for the change of bix to bbi. In compound 3, the Cu^I–bbi polymers form a supramolecular metal–organic host framework with rhombic channels in which the SiW₁₂ templates reside. Compound 4 shows a framework with hexagonal channels constructed by Cu^II–bbi coordination polymers which accommodated the SiW₁₂ templates.     

Diverse Ligand‐Functionalized Mixed‐Valent Hexamanganese Sandwiched Silicotungstates with Single‐Molecule Magnet Behavior

Under hydrothermal conditions, replacement of the water molecules in the [Mn^III₄Mn^II₂O₄(H₂O)₄]⁸⁺ cluster of mixed‐valent Mn₆ sandwiched silicotungstate [(B‐α‐SiW₉O₃₄)₂Mn^III₄Mn^II₂O₄(H₂O)₄]^12? ( 1 a ) with organic N ligands led to the isolation of five organic–inorganic hybrid, Mn₆‐substituted polyoxometalates (POMs) 2 – 6 . They were all structurally characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, diffuse‐reflectance spectroscopy, and powder and single‐crystal X‐ray diffraction. Compounds 2 – 6 represent the first series of mixed‐valent {Mn^III₄Mn^II₂O₄(H₂O)_4?n(L)_n} sandwiched POMs covalently functionalized by organic ligands. The preparation of 1 – 6 not only indicates that the double‐cubane {Mn^III₄Mn^II₂O₄(H₂O)_4?n(L)_n} clusters are very stable fragments in both conventional aqueous solution and hydrothermal systems and that organic functionalization of the [Mn^III₄Mn^II₂O₄(H₂O)₄]⁸⁺ cluster by substitution reactions is feasible, but also demonstrates that hydrothermal environments can promote and facilitate the occurrence of this substitution reaction. This work confirms that hydrothermal synthesis is effective for making novel mixed‐valent POMs substituted with transition‐metal (TM) clusters by combining lacunary Keggin precursors with TM cations and tunable organic ligands. Furthermore, magnetic measurements reveal that 3 and 6 exhibit single‐molecule magnet behavior.     

New Nanostructured Materials: Synthesis of Dodecanuclear NiII Complexes and Surface Deposition Studies

Microwave‐assisted synthesis has been used to obtain the family of dodecanuclear Ni^II complexes [Ni₁₂(NO₃)(MeO)₁₂(MeC₆H₄CO₂)₉(MeOH)₁₀(H₂O)₂][ClO₄]₂ ( 1 ), [Ni₁₂(NO₃)(MeO)₁₂(BrC₆H₄CO₂)₉(MeOH)₁₀(H₂O)₂][ClO₄]₂ ( 2 ), [Ni₁₂(CO₃)(MeO)₁₂(MeC₆H₄CO₂)₉(MeOH)₁₀(H₂O)₂]₂[SO₄] ( 3 ) and [Ni₁₂(NO₃)(MeO)₁₂(MeC₆H₄CO₂)₉(MeOH)₈(H₂O)₇][NO₃]₂ ( 4 ). They contain three {Ni₄O₄} cubane units which template around a central μ₆ anion, either NO₃^? or CO₃^2?. Their magnetic properties have been studied by superconducting quantum interference device (SQUID) magnetometry and high‐field EPR measurements. The nanostructuration of the Ni₁₂ species on mica surfaces is studied by AFM and grazing‐incidence X‐ray diffraction, which reveal the formation of polycrystalline thin layers.     

Syntheses,crystal structures,and magnetic properties of the banana-shaped tungstophosphates: [M6(H2O)2(PW9O34)2(PW6O26)]17− (MII=NiII,CoII)

Two new banana-shaped tungstophosphates [M₆(H₂O)₂(PW₉O₃₄)₂(PW₆O₂₆)]^{17 ?} (M^II?=?Ni^II, Co^II) incorporating two types of lacunary polyoxometalate units have been synthesized in aqueous solution and characterized by elemental analyses, IR, and UV spectra, and single-crystal X-ray diffraction. Structural analyses show that Na₆H₁₁[Ni₆(H₂O)₂(PW₉O₃₄)₂(PW₆O₂₆)]?·?32H₂O (1) and Na₇H₁₀[Co₆(H₂O)₂(PW₉O₃₄)₂(PW₆O₂₆)]?· 31H₂O (2) are generated from two tri-M^II substituted B-α-[(MOH₂)M₂PW₉O₃₄] Keggin units connected by a hexavacant [PW₆O₂₆]^11? Keggin fragment, leading to the M^II-containing banana-shaped tungstophosphates. Magnetic properties of 2 show decrease of the molar magnetic susceptibility at higher temperatures results from spin-orbit coupling of Co^II and antiferromagnetic interactions whereas the maximum at the lower temperatures is indicative of the ferromagnetic interactions within the trinuclear Co^II spin cluster in the sandwich belt.     

Cobalt(II) Complexes with N‐Thioacylamidophosphates and 2,2′‐Bipyridyl and 1,10‐Phenathroline. Crystal Structures,Solution 1H NMR Spectral and Magnetic Properties

Structure and magnetic properties of N‐diisopropoxyphosphorylthiobenzamide PhC(S)‐N(H)‐P(O)(OiPr)₂ ( HL^I ) and N‐diisopropoxyphosphoryl‐N′‐phenylthiocarbamide PhN(H)‐C(S)‐N(H)‐P(O)(OiPr)₂ ( HL^II ) complexes with the Co^II cation of formulas [Co{PhC(S)‐N‐P(O)(OiPr)₂}₂] ( 1 ), [Co{PhN(H)‐C(S)‐N‐P(O)(OiPr)₂}₂] ( 2 ), [Co{PhC(S)‐N(H)‐P(O)(OiPr)₂}₂{PhC(S)‐N‐P(O)(OiPr)₂}₂] ( 1a ) and [Co{PhC(S)‐N‐P(O)(OiPr)₂}₂}(2,2′‐bipy)] ( 3 ), [Co{PhC(S)‐N‐P(O)(OiPr)₂}₂(1,10‐phen)] ( 4 ), [Co{PhN(H)‐C(S)‐N‐P(O)(OiPr)₂}₂(2,2′‐bipy)] ( 5 ), [Co{PhN(H)‐C(S)‐N‐P(O)(OiPr)₂}₂(1,10‐phen)] ( 6 ) were investigated. Paramagnetic shifts in the ¹H NMR spectrum were observed for high‐spin Co^II complexes with HL^I,II , incorporating the S‐C‐N‐P‐O chelate moiety and two aromatic chelate ligands. Investigation of the thermal dependence of the magnetic susceptibility has shown that the extended materials 1‐2 and 6 show ferromagnetic exchange between distorted tetrahedral ( 1 , 2 ) or octahedral ( 1a , 6 ) metal atoms whereas 3 and 5 show antiferromagnetic properties. Compound 4 behaves as a spin‐canted ferromagnet, an antiferromagnetic ordering taking place below a critical temperature, T_c = 115 K. Complexes 1 and 1a were investigated by single crystal X‐ray diffraction. The cobalt(II) atom in complex 1 resides a distorted tetrahedral O₂S₂ environment formed by the C=S sulfur atoms and the P=O oxygen atoms of two deprotonated ligands. Complex 1a has a tetragonal‐bipyramidal structure, Co(O^ax)₂(O^eq)₂(S^eq)₂, and two neutral ligand molecules are coordinated in the axial positions through the oxygen atoms of the P=O groups. The base of the bipyramid is formed by two anionic ligands in the typical 1,5‐O,S coordination mode. The ligands are in a trans configuration.     

The Instability of Ni{N(SiMe3)2}2: A Fifty Year Old Transition Metal Silylamide Mystery

The characterization of the unstable Ni^II bis(silylamide) Ni{N(SiMe₃)₂}₂ ( 1 ), its THF complex Ni{N(SiMe₃)₂}₂(THF) ( 2 ), and the stable bis(pyridine) derivative trans‐Ni{N(SiMe₃)₂}₂(py)₂ ( 3 ), is described. Both 1 and 2 decompose at ca. 25 °C to a tetrameric Ni^I species, [Ni{N(SiMe₃)₂}]₄ ( 4 ), also obtainable from LiN(SiMe₃)₂ and NiCl₂(DME). Experimental and computational data indicate that the instability of 1 is likely due to ease of reduction of Ni^II to Ni^I and the stabilization of 4 through dispersion forces.     

Exploring the Symmetry,Structure, and Self‐Assembly Mechanism of a Gigantic Seven‐Fold Symmetric {Pd84} Wheel

The symmetry, structure and formation mechanism of the structurally self‐complementary { Pd₈₄ } = [Pd₈₄O₄₂(PO₄)₄₂(CH₃CO₂)₂₈]⁷⁰⁻ wheel is explored. Not only does the symmetry give rise to a non‐closest packed structure, the mechanism of the wheel formation is proposed to depend on the delicate balance between reaction conditions. We achieve the resolution of gigantic polyoxopalladate species through electrophoresis and size‐exclusion chromatography, the latter has been used in conjunction with electrospray mass spectrometry to probe the formation of the ring, which was found to proceed by the stepwise aggregation of {Pd₆}⁻ = [Pd₆O₄(CH₃CO₂)₂(PO₄)₃Na_6−nH_n]⁻ building blocks. Furthermore, the higher‐order assembly of these clusters into hollow blackberry structures of around 50 nm has been observed using dynamic and static light scattering.     

Assembly of a Supramolecular Architecture Based on Keggin POMs and Lanthanide Coordination Cations

Two new compounds based on Keggin polyoxometalates (POMs) [SiW₁₂O₄₀]⁴⁻ (SiW₁₂), [Na(H₂O)₃(H₂L)SiW₁₂O₄₀](H₂L)₂   6H₂O (1), and [Ce(H₂O)₃(HL)₂(H₂L)]₂[SiW₁₂O₄₀]₂ 10H₂O (2) (HL = C₆H₅NO₂ = isonicotinic acid), have been conventionally synthesized and characterized by routine methods. Compound 1 possesses a 1D right-handed helical structure constructed by SiW₁₂O₄₀ ⁴⁻ {SiW₁₂} and [Na(H₂O)₃(HL)] complexes. Interestingly, these right-handed helical chains are linked together via H-bonds forming a novel chiral layer. By using the similar synthesis method to that for compound 1, except for employing Ce³⁺ cations in instead of La³⁺ cations, a 3D supramolecular compound 2 based on SiW₁₂ and Ce³⁺ coordination cations has been obtained, which contains 1D channels along a axis. Additionally, the luminescence properties of 2 were studied. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A Systematic Exploration of Nickel–Pyrazolinato Chemistry with Alkali Metals: New Cages From Serendipitous Assembly

The preparation and properties of fourteen novel paramagnetic [Ni^II_x] aggregates bridged by pivalate, pyrazolinolate and in most cases hydroxide are reported. A rich structural diversity has been achieved by changing the nature of the alkali of the base used during the synthesis, leading to the nuclearities [Ni^II₄Na^I₄] ( 2, 3, 4 ), [Ni^II₅Na^I₄] ( 5, 6, 7 ), [Ni^II₅Li^I₆] ( 8 ), [Ni^II₈M^I₂] (M=K ( 9, 10 ), Rb ( 11, 12 ), Cs ( 13, 14 ) and [Ni^II₈] ( 15 ). All compounds have been characterised by single‐crystal Xray diffraction; however, full crystallographic details are given only for the representative molecules [Ni₄Na₄(fpo)₄(piv)₈(Hpiv)₈] ( 2 ), [Ni₅Na₄(OH)₂(mpo)₄(piv)₈(Hpiv)₂(MeCN)₂] ( 5 ), [Ni₅Li₆(OH)₂(fpo)₂(piv)₁₂(Hpiv)₄] ( 8 ), [Ni₈K₂(OH)₄(ppo)₄(piv)₁₀(Hppo)₂(Hpiv)₂(MeCN)₂] ( 9 ), [Ni₈Rb₂(OH)₄(ppo)₄(piv)₁₀(Hppo)₂(Hpiv)₂(MeCN)₂] ( 11 ), [Ni₈Cs₂(OH)₄(ppo)₄(piv)₁₀(Hppo)₂(Hpiv)₂(MeCN)₂] ( 13 ) and [Ni₈(OH)₄(mpo)₂(PhCH₂CO₂)₁₀(Hmpo)₈] ( 15 ). Variable‐temperature bulk magnetisation measurements have been performed for each type of complex. The [Ni^II₄Na^I₄] clusters show intramolecular antiferromagnetic coupling and a spin ground state of S=0. Complexes of the type [Ni^II₅Na^I₄] also display antiferromagnetic superexchange, leading to an S=1 spin ground state. The molecule with nuclearity [Ni^II₅Li^I₆], in contrast, exhibits ferromagnetic interactions, resulting in the presence of low energy states with high multiplicity, and a spin ground state S>1. The [Ni^II₈M^I₂] and [Ni^II₈] clusters have the same topology of spin carriers, which display predominantly antiferromagnetic interactions to yield a diamagnetic ground state. The coupling within these octanuclear Ni^II clusters is rationalised in terms of the nature of the Ni‐O‐Ni angles within the core.     

Two isomorphous transition metal complexes containing a protonated diaminopurine ligand: diaquabis(2,6‐diamino‐7H‐purin‐1‐ium‐κN9)bis(homophthalato‐κO)nickel(II) tetrahydrate and the cobalt(II) analogue

The two isomorphous title compounds, [M(C₅H₇N₆)₂(C₉H₆O₄)₂(H₂O)₂]·4H₂O or M²⁺(Hdap⁺)₂(hpt²⁻)₂(H₂O)₂·4H₂O {where dap is 2,6‐diaminopurine, H₂hpt is homophthalic acid [2‐(2‐carboxyphenyl)acetic acid] and M is Ni^II or Co^II}, consist of neutral M²⁺(Hdap⁺)₂(hpt²⁻)₂(H₂O)₂ monomers, where the M^II cation lies on an inversion centre and its MN₂O₄ octahedral environment is defined by one N atom (from Hdap⁺), two O atoms (from one hpt²⁻ dianion and one water molecule) and their inversion images. The structures are unusual in that the Hdap⁺ cation occurs in an uncommon protonated state (as 2,6‐diamino‐7H‐purin‐1‐ium) and both ligands bind in an unprecedented monodentate fashion. The existence of a large number of donors and acceptors for hydrogen bonding, together with π–π interactions, leads to a rather complex three‐dimensional structure.