From Gas Phase Observations to Solid State Reality: The Identification and Isolation of Trinuclear Salicylaldoximato Copper Complexes.

Conditions have been identified in which phenolic aldoximes and ketoximes of the types used in commercial solvent extraction processes can be doubly deprotonated and generate polynuclear Cu complexes with lower extractant:Cu molar ratios than those found in commercial operations. Electrospray mass spectrometry has provided an insight into the solution speciation in extraction experiments and has identified conditions to allow isolation and characterization of polynuclear Cu-complexes. Elevation of pH is effective in enhancing the formation of trinuclear complexes containing planar {Cu3-µ3-O}4+ or {Cu3-µ3-OH}5+ units. DFT calculations suggest that such trinuclear complexes are more stable than other polynuclear species. Solid structures of complexes formed by a salicylaldoxime with a piperidino substituent ortho to the phenolic OH group (L9H2) contain two trinuclear units in a supramolecular assembly, {[Cu3OH(L9H)3(ClO4)](ClO4)} 2, formed by H-bonding between the central {Cu3-µ3-OH}5+ units and oxygen atoms in the ligands of an adjacent complex. Whilst the lower ligand:Cu molar ratios provide more efficient Cu-loading in solvent extraction processes, the requirement to raise the pH of the aqueous phase to achieve this will make it impractical in most commercial operations because extraction will be accompanied by the precipitation (as oxyhydroxides) of Fe(III) which is present in significant quantities in feed solutions generated by acid leaching of most Cu ores.

Chromophore Multiplication To Enable Exciton Delocalization and Triplet Diffusion Following Singlet Fission in Tetrameric Pentacene.

A tetrameric pentacene, PT, has been used to explore the effects of exciton delocalization on singlet fission (SF). For the first time, triplet decorrelation through intramolecular triplet diffusion was observed following SF. Transient absorption spectroscopy was used to examine different decorrelation mechanisms (triplet diffusion versus structural changes) for PT and its dimeric equivalent PD on the basis of the rate and activation barrier of the decorrelation step. Charge-separation experiments using tetracyano-p-quinodimethane (TCNQ) to quench triplet excitons formed through SF demonstrate that enhanced intersystem crossing, that is, spin catalysis, is a widely underestimated obstacle to quantitative harvesting of the SF products. The importance of spatial separation of the decorrelated triplet states is emphasized, and independent proof that the decorrelated triplet pair state consists of two (T1 ) states per molecule is provided.

Controlling excimer formation in indolo[3,2,1-jk]carbazole/9H-carbazole based host materials for RGB PhOLEDs.

Three novel materials (5CzICz, Cz2ICz and Cz3ICz), based on the indolo[3,2,1-jk]carbazole and 9H-carbazole building blocks, with high triplet energies (E T > 2.80 eV) and good thermal stability (T g > 101 °C) were synthesized, characterized and applied as host materials in PhOLED devices. In course of the preparation of the materials, an improved protocol for the synthesis of the indolo[3,2,1-jk]carbazole moiety has been developed. The careful molecular design of the title compounds allowed to avoid excimer formation of the indolo[3,2,1-jk]carbazole subunits in thin films. Therefore, the improved molecular design broadened the applicability of indolo[3,2,1-jk]carbazole host materials and significantly enhanced the efficiency of PhOLED devices based on these derivatives compared to previously reported indolo[3,2,1-jk]carbazole based compounds. Accordingly, employing the newly developed materials red (CEmax: 32.7 cd A-1, PEmax: 31.0 lm W-1, EQEmax: 20.4%), green (CEmax: 81.0 cd A-1, PEmax: 87.4 lm W-1, EQEmax: 21.5%) and blue (CEmax: 35.5 cd A-1, PEmax: 39.9 lm W-1, EQEmax: 18.0%) PhOLED devices with a remarkably low efficiency roll-off at 1000 cd m-2 (Cz2ICz - red: 5%; green: 0%; blue: 6%) were fabricated.

Reversible Pressure-Controlled Depolymerization of a Copper(II)-Containing Coordination Polymer.

A unique pressure-induced Cu-N bond breaking/bond forming reaction is reported. The variation of pressure on a single crystal of a one-dimensional copper- (II)-containing coordination polymer (Cu2 L2 (1-methylpiperazine)2 ]n , where H2 L is 1,1'-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione)), was monitored using single crystal X-ray diffraction with the aid of a diamond anvil cell. At a very low elevated pressure (≈0.05 GPa) a remarkable reversible phase change was observed. The phase change results in the depolymerization of the material through the cleavage and formation of axial Cu-N bonds as well as "ring flips" of individual axially coordinated 1-methylpiperazine ligands. Overall, the pressure-induced phase change is associated with a surprising (and non-intuitive) shift in structure-from a 1-dimensional coordination polymer to a discrete dinuclear complex.

Unified model for singlet fission within a non-conjugated covalent pentacene dimer.

When molecular dimers, crystalline films or molecular aggregates absorb a photon to produce a singlet exciton, spin-allowed singlet fission may produce two triplet excitons that can be used to generate two electron-hole pairs, leading to a predicted ∼50% enhancement in maximum solar cell performance. The singlet fission mechanism is still not well understood. Here we report on the use of time-resolved optical and electron paramagnetic resonance spectroscopy to probe singlet fission in a pentacene dimer linked by a non-conjugated spacer. We observe the key intermediates in the singlet fission process, including the formation and decay of a quintet state that precedes formation of the pentacene triplet excitons. Using these combined data, we develop a single kinetic model that describes the data over seven temporal orders of magnitude both at room and cryogenic temperatures.

Thermally activated delayed fluorescence (TADF) and enhancing photoluminescence quantum yields of [Cu(I)(diimine)(diphosphine)](+) complexes-photophysical, structural, and computational studies.

The complexes [Cu(I)(POP)(dmbpy)][BF4] (1) and [Cu(I)(POP)(tmbpy)][BF4] (2) (dmbpy = 4,4'-dimethyl-2,2'-bipyridyl; tmbpy = 4,4',6,6'-tetramethyl-2,2'-bipyridyl; POP = bis[2-(diphenylphosphino)-phenyl]ether) have been studied in a wide temperature range by steady-state and time-resolved emission spectroscopy in fluid solution, frozen solution, and as solid powders. Emission quantum yields of up to 74% were observed for 2 in a rigid matrix (powder), substantially higher than for 1 of around 9% under the same conditions. Importantly, it was found that the emission of 2 at ambient temperature represents a thermally activated delayed fluorescence (TADF) which renders the compound to be a good candidate for singlet harvesting in OLEDs. The role of steric constraints within the complexes, in particular their influences on the emission quantum yields, were investigated by hybrid-DFT calculations for the excited triplet state of 1 and 2 while manipulating the torsion angle between the bipyridyl and POP ligands. Both complexes showed similar flexibility within a ±10° range of the torsion angle; however, 2 appeared limited to this range, whereas 1 could be further twisted with little energy demand. It is concluded that a restricted flexibility leads to a reduction of nonradiative deactivation and thus an increase of emission quantum yield.

Hierarchical assembly of discrete copper(II) metallo-structures from pre-assembled dinuclear (bis-ß-diketonato)metallocycles and flexible difunctional co-ligands.

The sequential interaction of preformed [Cu2(L1)2(THF)2] (where H2L1 is 1,1-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione incorporating a 1,3-phenylene linker between its two ß-diketone domains) and [Cu2(L4)2]·2H2O (where H2L4 is 1,1-(4,4'-oxybiphenylene)-bis(4,4-dimethylpentane-1,3-dione) incorporating a flexible oxybiphenylene linkage between the two ß-diketone groups) with the potentially difunctional aliphatic non-planar co-ligands, N-methylpiperazine (mpip), N,N'-dimethylpiperazine (dmpip) and 1,4-thiomorpholine (thiomorph) is reported. A series of extended molecular assemblies exhibiting a range of di- and tetranuclear assemblies were obtained and their X-ray structures determined. Dinuclear [Cu2(L1)2(mpip)2]·2mpip incorporates two 5-coordinate, square pyramidal metal centres as does tetranuclear [{Cu2(L1)2}2(dmpip)2]·2dmpip. In contrast, dinuclear [Cu2(L1)2(dmpip)4]·dmpip and [{Cu2(L1)2}2(thiomorph)4]·3thiomorph each contain two 5-coordinate and two 6-coordinate centres. Each of [Cu2(L4)2(THF)2]·2THF and Cu2(L4)2(mpip)2]·H2O incorporate only 5-coordinate metal centres, with the latter complex forming a one-dimensional hydrogen bonded ribbon-like structure directed along the crystallographic a-axis. In keeping with the documented tendency for the smallest, least strained assembly to form in supramolecular self-assembly processes, the incorporation of the flexible "oxy" linkage between the 4,4'-linked phenylene rings of H2L3 results in generation of a dinuclear [Cu2L2] species rather than a trinuclear (triangular) [Cu3L3] species of the type formed by the more rigid bis-ß-diketonato ligand analogue in which the biphenylene rings separating the ß-diketone domains are directly coupled in their 4,4' positions.

Photo-isomerisation of alkenyl complexes of platinum(II): structural, spectroscopic, kinetic and computational investigations.

In this work UVA and blue light have been used to study photo-isomerisation about the C=C double bond in complexes of the type [PtCl(-CH=CHAr)(tmeda)] [Ar = C6H5, (E)-2a; 4-CH3O-C6H4, (E)-2b; 3-NO2-C6H4, (E)-2c; and 3-CH3O-C6H4, (E)-2d]. The progress of the reaction has been monitored by NMR spectroscopy following irradiation of the NMR sample. The NMR data have been complemented with X-ray diffractometric analysis of compounds (E)-2a-c and (Z)-2a. The kinetic data clearly indicate that a monomolecular mechanism is operating with the energy of the irradiating light influencing the rate of isomerisation but not the equilibrium composition, which is only slightly in favour of the Z isomer. DFT and TD-DFT theoretical investigations have been carried out to elucidate the nature of the main electronic transitions in the UV-Vis region and the mechanism of the photo-isomerisation reaction appears to proceed through a C=C bond twist process similar to that involved in purely organic molecules such as stilbene. In the Z isomer, one ortho proton of the phenyl group can come close to platinum (Pt···H(ortho) distance of 2.632 Å in (Z)-2a). In the case of 2c, the difference in chemical shift between the two ortho protons varies from 3.30 ppm in the Z isomer, where interaction with Pt is possible, to 0.60 ppm in the E isomer, where such interaction cannot take place. The analysis of the DFT orbitals indicates that the most shifted H(ortho) is that with a greater positive charge, pointing to an H-bond type of interaction.

Metalloligands containing aminofulvene-aldiminate (AFA) ligands and their bimetallic complexes.

A simple and convenient route to η(5)-coordinated Ru and Rh aminofulvene-aldiminate (AFA) complexes is described. The metalloligands [Cp*Ru{η(5)-(Ph(2)AFAH)}][BF(4)] (3), [Cp*Ru{η(5)-(benzyl(2)AFAH)}][OTf] (7), [Cp*Rh{η(5)-(Cy(2)AFA)H}][BF(4)](2) (8) and [Cp*Rh{η(5)-(Cy(2)AFA)}][BF(4)] (9) have been synthesised and characterised. The basicity of 9 has been found to be significantly less than its neutral analogue and thus eliminates the need for a deprotonation step to ligate to a second metal in the κ(2)-N,N'-coordination mode. The reaction of 9 with a palladium precursor provides a mixed-metal complex [Cp*Rh(η(5)/κ(2)-Cy(2)AFA)PdCl(2)][BF(4)] (12). Cyclic voltammetry studies of the Ph(2)AFAH ligand shows an irreversible one electron oxidation peak at +1.0 V (vs. Fc/Fc(+)). Complex 3 shows an irreversible oxidation at +1.5 V and a reduction peak at -1.0 V. The oxidation of 3 occurs on the AFA ligand backbone whereas the structurally analogous neutral 1,2-bis(imidoyl)pentamethyl-ruthenocene shows reversible oxidation at the Ru center.

Design and function of pre-organised outer-sphere amidopyridyl extractants for zinc(II) and cobalt(II) chlorometallates: the role of C-H hydrogen bonds.

Four new sterically hindered pyridines, L(1)-L(4)-containing amido substituents at the 2-position act as efficient solvent extractants for [CoCl(4)](2-) or [ZnCl(4)](2-) from acidic chloride solutions through protonation of the pyridino N-centre to form the neutral outer-sphere complexes [(LH)(2)MCl(4)]. These ionophores show very high selectivity for chlorometallate anions over chloride ion and are readily stripped to liberate the free-metal chlorides without the formation of inner-sphere complexes [ML(2)Cl(2)]. Single-crystal X-ray structure determinations of [(L(2)H)(2)CoCl(4)] and [(L(2)H)(2)ZnCl(4)] (L(2) = 2-(4,6-di-tert-butylpyridin-2-yl)-N,N'-dihexylmalonamide) coupled with (1)H NMR spectroscopy and DFT calculations on L(2)H(+) and other complexes of [ZnCl(4)](2-) confirm that the pyridinium NH group does not address the outer co-ordination sphere of the metallanion, but rather forms a hydrogen bond to the pendant amide groups and thus pre-organizes the ligand to present both C-H and amido N-H hydrogen-bond donors to the [MCl(4)](2-) ions. The selectivity for chlorometallates over chloride ions shown by this class of extractants arises from their ability to present several polarized C-H units towards the charge-diffuse ions [MCl(4)](2-), whereas the smaller, "harder" chloride anion prefers to be associated with the amido N-H hydrogen-bond donors.

Family of carboxylate- and nitrate-diphenoxo triply bridged dinuclear Ni(II)Ln(III) complexes (Ln = Eu, Gd, Tb, Ho, Er, Y): synthesis, experimental and theoretical magneto-structural studies, and single-molecule magnet behavior.

Seven acetate-diphenoxo triply bridged M(II)-Ln(III) complexes (M(II) = Ni(II) and Ln(III) = Gd, Tb, Ho, Er, and Y; M(II) = Zn(II) and Ln(III) = Ho(III) and Er(III)) of formula [M(µ-L)(µ-OAc)Ln(NO(3))(2)], one nitrate-diphenoxo triply bridged Ni(II)-Tb(III) complex, [Ni(µ-L)(µ-NO(3))Tb(NO(3))(2)]·2CH(3)OH, and two diphenoxo doubly bridged Ni(II)-Ln(III) complexes (Ln(III) = Eu, Gd) of formula [Ni(H(2)O)(µ-L)Ln(NO(3))(3)]·2CH(3)OH have been prepared in one pot reaction from the compartmental ligand N,N',N"-trimethyl-N,N"-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H(2)L). Moreover, Ni(II)-Ln(III) complexes bearing benzoate or 9-anthracenecarboxylate bridging groups of formula [Ni(µ-L)(µ-BzO)Dy(NO(3))(2)] and [Ni(µ-L)(µ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN have also been successfully synthesized. In acetate-diphenoxo triply bridged complexes, the acetate bridging group forces the structure to be folded with an average hinge angle in the M(µ-O(2))Ln bridging fragment of ~22°, whereas nitrate-diphenoxo doubly bridged complexes and diphenoxo-doubly bridged complexes exhibit more planar structures with hinge angles of ~13° and ~2°, respectively. All Ni(II)-Ln(III) complexes exhibit ferromagnetic interactions between Ni(II) and Ln(III) ions and, in the case of the Gd(III) complexes, the J(NiGd) coupling increases weakly but significantly with the planarity of the M-(O)(2)-Gd bridging fragment and with the increase of the Ni-O-Gd angle. Density functional theory (DFT) theoretical calculations on the Ni(II)Gd(III) complexes and model compounds support these magneto-structural correlations as well as the experimental J(NiGd) values, which were found to be ~1.38 and ~2.1 cm(-1) for the folded [Ni(µ-L)(µ-OAc)Gd(NO(3))(2)] and planar [Ni(H(2)O)(µ-L)Gd(NO(3))(3)]·2CH(3)OH complexes, respectively. The Ni(II)Dy(III) complexes exhibit slow relaxation of the magnetization with Δ/k(B) energy barriers under 1000 Oe applied magnetic fields of 9.2 and 10.1 K for [Ni(µ-L)(µ-BzO)Dy(NO(3))(2)] and [Ni(µ-L)(µ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN, respectively.

Structural, magnetic, and electronic properties of phenolic oxime complexes of Cu and Ni.

Square planar complexes of the type Ni(L(1))(2), Ni(L(2))(2), Cu(L(1))(2), and Cu(L(2))(2), where L(1)H = 2-hydroxy-5-t-octylacetophenone oxime and L(2)H = 2-hydroxy-5-n-propylacetophenone oxime, have been prepared and characterized by single-crystal X-ray diffraction, cyclic voltammetry, UV/vis spectroscopy, field-effect-transistor measurements, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations, and, in the case of the paramagnetic species, electron paramagnetic resonance (EPR) and magnetic susceptibility. Variation of alkyl groups on the ligand from t-octyl to n-propyl enabled electronic isolation of the complexes in the crystal structures of M(L(1))(2) contrasting with π-stacking interactions for M(L(2))(2) (M = Ni, Cu). This was evidenced by a one-dimensional antiferromagnetic chain for Cu(L(2))(2) but ideal paramagnetic behavior for Cu(L(1))(2) down to 1.8 K. Despite isostructural single crystal structures for M(L(2))(2), thin-film X-ray diffraction and scanning electron microscopy (SEM) revealed different morphologies depending on the metal and the deposition method (vapor or solution). The Cu complexes displayed limited electronic interaction between the central metal and the delocalized ligands, with more mixing in the case of Ni(II), as shown by electrochemistry and UV/vis spectroscopy. The complexes M(L(2))(2) showed poor charge transport in a field-effect transistor (FET) device despite the ability to form π-stacking structures, and this provides design insights for metal complexes to be used in conductive thin-film devices.

Strategy for the rational design of asymmetric triply bridged dinuclear 3d-4f single-molecule magnets.

Three triply bridged M(II)-Dy(III) dinuclear complexes, [Ni(µ-L)(µ-OAc)Dy(NO(3))(2)] 1, [Zn(µ-L)(µ-OAc)Dy(NO(3))(2)] 2, and [Ni(µ-L)(µ-NO(3))Dy(NO(3))(2)]·2CH(3)OH 3 were prepared with a new and flexible compartmental ligand, N,N',N″-trimethyl-N,N″-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylene triamine (H(2)L), containing N(3)O(2)-inner and O(4)-outer coordination sites. These complexes have diphenoxo/acetate (1 and 2) or diphenoxo/nitrate (3) asymmetric bridging fragments. Compounds 1 and 3 exhibit ferromagnetic interaction between Ni(2+) and Dy(3+) ions and frequency dependence of the out-of-phase (χ″(M)) alternating current (ac) susceptibility signal characteristic of single-molecule-magnet behavior. The energy barriers Δ/k(B) for compound 3 under zero and 1000 Oe applied direct current (dc) magnetic fields were estimated from the Arrhenius plots to be 7.6 and 19.1 K, respectively.

Encapsulation of a magnesium hydroxide cubane by a bowl-shaped polypyrrolic Schiff base macrocycle.

Hydrolysis of a Pacman-shaped binuclear magnesium complex of a polypyrrolic Schiff base macrocycle results in the formation of a new magnesium hydroxide cubane that is encapsulated by the macrocyclic framework through both coordinative and hydrogen-bonding interactions.

Using the outer coordination sphere to tune the strength of metal extractants.

A series of 3-substituted salicylaldoximes has been used to demonstrate the importance of outer-sphere interactions on the efficacy of solvent extractants that are used to produce approximately one-quarter of the world's copper. The distribution coefficient for extraction of copper by 5-tert-butyl-3-X-salicylaldoximes (X = H, Me, (t)Bu, NO(2), Cl, Br, OMe) varies by more than two orders of magnitude. X-ray structure determinations of preorganized free ligand dimers (10 new structures are reported) indicate that substituents with a hydrogen-bond acceptor atom attached to the 3-carbon atom, ortho to the phenolic oxygen, buttress the intermolecular hydrogen bond from the oximic proton. Density functional theory calculations demonstrate that this hydrogen-bond buttressing is maintained in copper(II) complexes and contributes significantly to their relative stabilities in energy-minimized gas-phase structures. A remarkable correlation between the order of the calculated enthalpies of formation of the copper complexes in the gas phase and the observed strength of the ligands as copper solvent extractants is ascribed to the low solvation energies of species in the water-immiscible phase and/or the similarities of the solvation enthalpies of the preorganized ligand dimers and their copper(II) complexes.

Donor-extended tripodal pyrroles: encapsulation, metallation, and H-bonded tautomers.

A tripodal iminopyrrole provides an environment suited to the encapsulation of water through hydrogen-bonding, and the formation of metal complexes by deprotonation and imine-pyrrole tautomerisation.

Hexagonal wheel formation through the hydrogen-bonded assembly of cobalt Pacman complexes.

A cobalt aquo-hydroxo complex of a ditopic Schiff-base pyrrole-crown ether macrocycle has been prepared and forms a rigid Pacman-clefted structure that assembles through hydrogen-bonding into a hexagonal wheel motif in the solid state.

Hexa- and octanuclear iron(III) salicylaldoxime clusters.

The syntheses, structures and magnetic properties of six iron complexes stabilised with the derivatised salicylaldoxime ligands Me-saoH(2) (2-hydroxyethanone oxime) and Et-saoH(2) (2-hydroxypropiophenone oxime) are discussed. The four hexanuclear and two octanuclear complexes of formulae [Fe(8)O(2)(OMe)(4)(Me-sao)(6)Br(4)(py)(4)]·2Et(2)O·MeOH (1·2Et(2)O·MeOH), [Fe(8)O(2)(OMe)(3.85)(N(3))(4.15)(Me-sao)(6)(py)(2)] (2), [Fe(6)O(2)(O(2)CPh-4-NO(2))(4)(Me-sao)(2)(OMe)(4)Cl(2)(py)(2)] (3), [Fe(6)O(2)(O(2)CPh-4-NO(2))(4)(Et-sao)(2)(OMe)(4)Cl(2)(py)(2)]·2Et(2)O·MeOH (4·2Et(2)O·MeOH), [HNEt(3)](2)[Fe(6)O(2)(Me-sao)(4)(SO(4))(2)(OMe)(4)(MeOH)(2)] (5) and [HNEt(3)](2)[Fe(6)O(2)(Et-sao)(4)(SO(4))(2)(OMe)(4)(MeOH)(2)] (6) all are built from a series of edge-sharing [Fe(4)(µ(4)-O)](10+) tetrahedra. Complexes 1 and 2 display a new µ(4)-coordination mode of the oxime ligand and join a small group of Fe-phenolic oxime complexes with nuclearity greater than six.

Antiferromagnetic versus ferromagnetic exchange interactions in bis(µ-O(oximate))dinickel(II) units for a series of closely related cube shaped carboxamideoximate-bridged Ni(4) complexes. A combined experimental and theoretical magneto-structural study.

The syntheses, crystal structures, and the experimental and theoretical magnetochemical characterization for three tetrametallic Ni(II) clusters, namely, [Ni(4)(L)(4)(Cl)(2)(MeOH)(2)](ClO(4))(2)·4MeOH (1), [Ni(4)(L)(4)(N(3))(2)(MeOH)(2)](ClO(4))(2)·2MeOH (2), and [Ni(4)(L1)(4)(pyz)(2)(PhCOO)(2)(MeOH)(2)](ClO(4))(2)·7MeOH (3) (where HL and HL1 represent bipyridine-2-carboxamideoxime and pyrimidine-2-carboxamideoxime, respectively) are reported. Within the Ni(4)(2+) units of these compounds, distorted octahedral Ni(II) ions are bridged by carboxamideoximato ligands to adopt a distorted tetrahedral disposition. The Ni(4)(2+) unit, of C(2) symmetry, can also be viewed as a cube with single [O-atom] and double [NO oxime] bridging groups as atom edges, which define two almost square-planar Ni(O)(2)Ni rings and four irregular hexagonal Ni(NO)(2)Ni rings. To analyze the magnetic properties of 1-3, we have considered the simplest two-J model, where J(1) = J(2) (exchange interactions between the Ni(II) ions belonging to the Ni(O)(2)Ni square rings) and J(a) = J(b) = J(c) = J(d) (exchange interactions between the Ni(II) ions belonging to the Ni-(NO)(2)Ni hexagonal rings) with the Hamiltonian H = -J(1)(S(1)S(2) + S(3)S(4)) - J(a)(S(1)S(3) + S(1)S(4) + S(2)S(3) + S(2)S(4)). The J(1) and J(a) values derived from the fitting of the experimental susceptibility data are -5.8 cm(-1) and -22.1 cm(-1) for 1; -2.4 cm(-1) and -22.8 cm(-1) for 2, and +15.6 cm(-1) and -10.8 cm(-1) for 3. The magneto-structural results and density-functional theory (DFT) calculations demonstrate that the exchange interactions inside the Ni(µ-O)(2)Ni square rings depend on the Ni-O-Ni bridging angle (θ) and the out-of-plane angle of the NO oximate bridging group with respect to the Ni(O)(2)Ni plane (τ), whereas the interactions propagated through the Ni-N-O(Ni)-Ni exchange pathways defining the side of the hexagonal rings depend on the Ni-N-O-Ni torsion angle (α). In both cases, theoretical magneto-structural correlations were obtained, which allow the prediction of the angle for which ferromagnetic interactions are expected. For compound 3, the existence of the axial magnetic exchange pathway through the syn-syn benzoate bridge may also contribute (in addition to the θ and τ angles) to the observed F interaction in this compound through orbital countercomplementarity, which has been supported by DFT calculations. Finally, DFT calculations clearly show that the antiferromagnetic exchange increases when the dihedral angle between the O-Ni-O planes of the Ni(µ-O)(2)Ni square ring, ß, increases.