Challenges for exploiting nanomagnet properties on surfaces.

Molecular complexes with single-molecule magnet (SMM) or qubit properties, commonly called molecular nanomagnets, are great candidates for information storage or quantum information processing technologies. However, the implementation of molecular nanomagnets in devices for the above-mentioned applications requires controlled surface deposition and addressing the nanomagnets' properties on the surface. This Perspectives paper gives a brief overview of molecular properties on a surface relevant for magnetic molecules and how they are affected when the molecules interact with a surface; then, we focus on systems of increasing complexity, where the relevant SMMs and qubit properties have been observed for the molecules deposited on surfaces; finally, future perspectives, including possible ways of overcoming the problems encountered so far are discussed.

Unusual Stabilisation of Remarkably Bent Tetra-Cationic Tetra-radical Intermolecular Fe(III) µ-Oxo Tetranuclear Complexes.

A hitherto unknown series of air stable, π-conjugated, remarkably bent tetra-cation tetra-radical intermolecular Fe(III) µ-oxo tetranuclear complex, isolated from the dication diradical diiron(III) porphyrin dimers, has been synthesised and spectroscopically characterised along with single crystal X-ray structure determination of two such molecules. These species facilitate long-range charge/radical delocalisation through the bridge across the entire tetranuclear unit manifesting an unusually intense NIR band. Assorted spin states of Fe(III) centres are stabilised within these unique tetranuclear frameworks: terminal six-coordinate iron centres stabilise the admixed intermediate spin states while the central five-coordinate iron centres stabilise the high-spin states. Variable temperature magnetic susceptibility measurements indicated strong antiferromagnetic coupling for the Fe(III)-O-Fe(III) unit while the exchange interactions between the Fe centres and the porphyrin π-cation radicals are weaker as supported both by magnetic data and DFT calculations. The nature of orbital overlap between the SOMOs of Fe(III) and π* orbital of the porphyrin was found to rationalise the observed exchange coupling, establishing such a complex magnetic exchange in this tetranuclear model with a significant bioinorganic relevance.

Controllable Structural Transformation of Non-Porous Propyl-Malonate Hexakis[60]fullerene by Chloroform Uptake/Release.

The design of dynamic structures with high recognition host-guest materials capable to host selectively small volatile molecules is an emergent field of research with both fundamental and applied implications. The challenge of exploring novel materials with advanced functionalities has led to the development of dynamic crystalline structures promoted by soft interactions. Here, a new pure organic dynamic framework based on hexakis[60]fullerene that are held together by weak van der Waals interactions is described. This crystalline structure is capable of absorbing and releasing chloroform, through internal structural reorganization. This research provides new insight into the design of organic molecular crystals for selective adsorption applications.

Luminescent and Magnetic Tb-MOF Flakes Deposited on Silicon.

The synthesis of a terbium-based 2D metal-organic framework (MOF), of formula [Tb(MeCOO)(PhCOO)2] (1), a crystalline material formed by neutral nanosheets held together by Van der Waals interactions, is presented. The material can be easily exfoliated by sonication and deposited onto different substrates. Uniform distributions of Tb-2D MOF flakes onto silicon were obtained by spin-coating. We report the luminescent and magnetic properties of the deposited flakes compared with those of the bulk. Complex 1 is luminescent in the visible and has a sizeable quantum yield of QY = 61% upon excitation at 280 nm. Photoluminescence measurements performed using a micro-Raman set up allowed us to characterize the luminescent spectra of individual flakes on silicon. Magnetization measurements of flakes-on-silicon with the applied magnetic field in-plane and out-of-plane display anisotropy. Ac susceptibility measurements show that 1 in bulk exhibits field-induced slow relaxation of the magnetization through two relaxation paths and the slowest one, with a relaxation time of τlf ≈ 0.5 s, is assigned to a direct process mechanism. The reported exfoliation of lanthanide 2D-MOFs onto substrates is an attractive approach for the development of multifunctional materials and devices for different applications.

Playing with the weakest supramolecular interactions in a 3D crystalline hexakis[60]fullerene induces control over hydrogenation selectivity.

Weak forces can play an essential role in chemical reactions. Controlling such subtle forces in reorganization processes by applying thermal or chemical stimuli represents a novel synthetic strategy and one of the main targets in supramolecular chemistry. Actually, to separate the different supramolecular contributions to the stability of the 3D assemblies is still a major challenge. Therefore, a clear differentiation of these contributions would help in understanding the intrinsic nature as well as the chemical reactivity of supramolecular ensembles. In the present work, a controlled reorganization of an hexakis[60]fullerene-based molecular compound purely governed by the weakest van der Waals interactions known, i.e. the dihydrogen interaction - usually called sticky fingers - is illustrated. This pre-reorganization of the hexakis[60]fullerene under mild conditions allows a further selective hydrogenation of the crystalline material via hydrazine vapors exposure. This unique two-step transformation process is monitored by single-crystal to single-crystal diffraction (SCSC) which allows the direct observation of the molecular movements in the lattice and the subsequent solid-gas hydrogenation reaction.

Carboxylate-Decorated Aggregation of Octanuclear Co4Ln4 (Ln = Dy, Ho, Yb) Complexes from Ligand-Controlled Hydrolysis: Synthesis, Structures, and Magnetic Properties.

One-pot reactions of an asymmetric carboxy-ether-phenol based Schiff base H2L (2-((2-hydroxy-3-methoxybenzylidene)amino)benzoic acid) with selected Ln(NO3)3·nH2O and [Co2(µ-OH2)(O2CCMe3)4(HO2CCMe3)4] (Co2-Piv) in basic MeOH medium resulted in a family of three octanuclear complexes, [CoII4LnIII4L4(µ1,3-Piv)4(µ1,1,3-Piv)2(η1-Piv)2(µ3-OH)4(MeOH)2]·mMeOH·nH2O (Ln = Dy; m = 3, n = 1 (1), Ho; m = 4, n = 0 (2), Yb; m = 3, n = 1 (3)). The coordination aggregates thus obtained were nicely sustained by four ligand anions and eight externally added carboxylate anions showing three different modes of intermetallic connectivity. The options for incorporating different 4f ions in an investigative synthesis, without altering the resulting intermetallic core structure, were successful for the three representative examples. Single-crystal X-ray diffraction studies revealed that the compounds are isostructural and built from two initially formed partial dicubane-type Co2Ln2L2 units. In each of the tetranuclear parts, the metal ion centers are held together by two L2-, two µ3-HO-, three Piv- bridges, one terminal Piv-, and one terminal MeOH. Four carboxylate ends of four L2- units are responsible for connecting two Co2Ln2 units into octanuclear structures. The unique distortion around the CoII centers is achieved from the facile coordination of bigger 4f ions to the adjacent hard OO sites. The distortion is further maintained by the presence of terminal COO- groups from L2-. The dc magnetic susceptibility data revealed ferromagnetic coupling between the CoII and LnIII centers within the series, whereas the ac magnetic susceptibility measurements identified only 1, having a highly anisotropic DyIII ion, as a single-molecule magnet in the absence of any external magnetic field, with an energy barrier Ueff of 12.5 K.

Heterometallic Co-Dy SMMs grafted on iron oxide nanoparticles.

Heterometallic 3d-4f SMM [Co4Dy(OH)2(SALOH)5(chp)4(MeCN)(H2O)2] (1) has been deposited onto iron oxide nanoparticles (NPs) with an oleate self-assembled monolayer (SAM) as a surfactant. The obtained hybrid molecular-inorganic system 1-NP has been thoroughly characterized. The oleate SAM separates SMM 1 from the magnetic substrate to avoid the strong-coupling between the surface and molecule to ensure that 1 retains its magnetic properties in 1-NP. The magnetic properties of the hybrid system 1-NP have been characterized by element specific XMCD: the heterometallic SMM retains its magnetic properties on the surface of the iron oxide NPs while there is an enhancement of the magnetic properties of the NPs.

A Multifunctional Dysprosium-Carboxylato 2D Metall-Organic Framework.

We report the microwave assisted synthesis of a bidimensional (2D) MOF of formula [Dy(MeCOO)(PhCOO)2 ]n (1) and its magnetically diluted analogue [La0.9 Dy0.1 (MeCOO)(PhCOO)2 ] (1 d). 1 is a 2D material with single-ion-magnet (SIM) behaviour and 1 d is a multifunctional, magnetic and luminescent 2D material. 1 can be exfoliated into stable nanosheets by sonication.

Octanuclear Ni4 Ln4 Coordination Aggregates from Schiff Base Anion Supports and Connecting of Two Ni2 Ln2 Cubes: Syntheses, Structures, and Magnetic Properties.

A family of 3d-4f aggregates have been reported through guiding the dual coordination modes of ligand anion (HL- ) and in situ generated ancillary bridge driven self-assembly coordination responses toward two different types of metal ions. Reactions of lanthanide(III) nitrate (Ln=Gd, Tb, Dy, Ho and Yb), nickel(II) acetate and phenol-based ditopic ligand anion of 2-[{(2-hydroxypropyl)imino}methyl]-6-methoxyphenol (H2 L) in MeCN-MeOH (3 : 1) mixture and LiOH provided five new octanuclear Ni-4f coordination aggregates from two Ni2 Ln2 cubanes. Single-crystal X-ray diffraction analysis reveals that all the members of the family are isostructural, with the central core formed from the coupling of two distorted [Ni2 Ln2 O4 ] heterometallic cubanes [Ni2 Ln2 (HL)2 (µ3 -OH)2 (OH)(OAc)4 ]+ (Ln=Gd (1), Tb (2), Dy (3), Ho (4) and Yb (5)). Higher coordination demand of 4f ions induced the coupling of the two cubes by (OH)(OAc)2 bridges. Variable temperature magnetic study reveals weak coupling between the Ni2+ and Ln3+ ions. For the Tb (2) and Dy (3) analogs, the compounds are SMMs without an applied dc field, whereas the Gd (1) analogue is not an SMM. The observation revealed thus that the anisotropy of the Ln3+ ions is central to display the SMM behavior within this structurally intriguing family of compounds.

Cathecol and Naphtol Groups in Salphen-Type Schiff Bases for the Preparation of Polynuclear Complexes.

In this paper, we show a strategy to modify salphen-type Schiff base ligands with naphtol (SYML1) and pyrocathecol (2,3-dihydroxyphenyl) groups (SYML2), or a combination of both (ASYML). Each of these ligands can be used to obtain polynuclear metal complexes following two different strategies. One relies on using metals that are either too large for the N2O2 cavity or not fond of coordination number 4 and the other one relies on forcing the polynuclear species by adding functional groups to the hydroxybenzaldehayde in order to have extra coordination sites in the ligand. We report and characterize the mononuclear complexes SYML1-Cu and SYML1-Ce, along with the dinuclear complex SYML1-Fe and the tetranuclear species SYML2-Mn. The asymmetric ligand ASYML routinely hydrolyzes into the symmetric ligands in the reaction mixtures. SYML1-Fe displays a nearly linear Fe-O-Fe bridge with very strong antiferromagnetic coupling between the Fe(III) ions.

Molecular enneanuclear CuII phosphates containing planar hexanuclear and trinuclear sub-units: syntheses, structures, and magnetism.

Highly symmetric enneanuclear copper(ii) phosphates [Cu9(Pz)6(µ-OH)3(µ3-OH)(ArOPO3)4(DMF)3] (PzH = pyrazole, Ar = 2,6-(CHPh2)2-4-R-C6H2; R = Me, 2MeAr; Et, 2EtAr; iPr, 2iPrAr; and Ar = 2,6-iPr2C6H3, 2Dip) comprising nine copper(ii) centers and pyrazole, hydroxide and DMF as ancillary ligands were synthesized by a reaction involving the arylphosphate monoester, 1, copper(i)chloride, pyrazole, and triethylamine in a 4 : 9 : 6 : 14 ratio. All four complexes were characterized by single crystal structural analysis. The complexes contain two distinct structural motifs within the multinuclear copper scaffold: a hexanuclear unit and a trinuclear unit. In the latter, the three Cu(ii) centres are bridged by a µ3-OH. Each pair of Cu(ii) centers in the trinuclear unit are bridged by a pyrazole ligand. The hexanuclear unit is made up of three dinuclear Cu(ii) motifs where the two Cu(ii) centres are bridged by an -OH and a pyrazole ligand. The three dinuclear units are connected to each other by phosphate ligands. The latter also aid the fusion of the trinuclear and the hexanuclear motifs. Magnetic studies reveal a strong antiferromagnetic exchange between the Cu(ii) centres of the dinuclear units in the hexanuclear part and a strong spin frustration in the trinuclear part leading to a degenerate ground state.

Valence tautomerism and spin crossover in pyridinophane-cobalt-dioxolene complexes: an experimental and computational study.

Compounds [Co(L-N4R2)(dbdiox)](BPh4) (L-N4R2 = N,N'-di-alkyl-2,11-diaza[3.3]-(2,6)pyridinophane, R = iPr (1a), Et (2a); dbdiox = 3,5-di-tert-butyldioxolene) and [M(L-N4iPr2)(dbdiox)](BPh4) (M = Mn (3a), Fe (4a)) have been synthesized and investigated with a view to possible valence tautomeric (VT) or spin crossover (SCO) interconversions. Single crystal X-ray diffraction data for all compounds at 100 or 130 K indicate trivalent metal cations and di-tert-butylcatecholate (dbcat2-) dioxolene ligands. Variable temperature magnetic susceptibility data for all species between 2 and 340 K are consistent with these redox states, with low spin configurations for the cobalt(iii) ions and high spin for the manganese(iii) and iron(iii) ions. Above 340 K, compound 1a exhibits an increase in magnetic susceptibility, suggesting the onset of a VT interconversion from low spin Co(iii)-dbcat to high spin Co(ii)-dbsq (dbsq- = di-tert-butylsemiquinonate) that is incomplete up to 400 K. In solution, variable temperature electronic absorption spectra and Evans NMR method magnetic susceptibility data indicate reversible VT interconversions for 1a in several solvents, with the transition temperature varying with solvent. Variable temperature electronic absorption spectra are temperature-invariant for 3a and 4a, while spectra for 2a in 1,2-dichloroethane suggest the onset of a VT transition at the highest temperatures measured. Density functional theory calculations on all four compounds and literature analogues provide key insights into the relative energies of the different electromeric forms and the possibilities for VT versus SCO interconversions in this family of compounds.

A Three-Dimensional Dynamic Supramolecular "Sticky Fingers" Organic Framework.

Engineering high-recognition host-guest materials is a burgeoning area in basic and applied research. The challenge of exploring novel porous materials with advanced functionalities prompted us to develop dynamic crystalline structures promoted by soft interactions. The first example of a pure molecular dynamic crystalline framework is demonstrated, which is held together by means of weak "sticky fingers" van der Waals interactions. The presented organic-fullerene-based material exhibits a non-porous dynamic crystalline structure capable of undergoing single-crystal-to-single-crystal reactions. Exposure to hydrazine vapors induces structural and chemical changes that manifest as toposelective hydrogenation of alternating rings on the surface of the [60]fullerene. Control experiments confirm that the same reaction does not occur when performed in solution. Easy-to-detect changes in the macroscopic properties of the sample suggest utility as molecular sensors or energy-storage materials.

Electric-field induced bistability in single-molecule conductance measurements for boron coordinated curcuminoid compounds.

We have studied the single-molecule conductance of a family of curcuminoid molecules (CCMs) using the mechanically controlled break junction (MCBJ) technique. The CCMs under study contain methylthio (MeS-) as anchoring groups: MeS-CCM (1), the free-ligand organic molecule, and two coordination compounds, MeS-CCM-BF2 (2) and MeS-CCM-Cu (3), where ligand 1 coordinates to a boron center (BF2 group) and to a CuII moiety, respectively. We found that the three molecules present stable molecular junctions allowing detailed statistical analysis of their electronic properties. Compound 3 shows a slight increase in the conductance with respect to free ligand 1, whereas incorporation of BF2 (compound 2) promotes the presence of two conductance states in the measurements. Additional experiments with control molecules point out that this bistability is related to the combination of MeS- anchoring groups and the BF2 moiety within the structure of the molecules. Theoretical calculations show that this can be explained by the presence of two conformers once compound 2 is anchored between the gold electrodes. An energy minimum is found for a flat structure but there is a dramatic change in the magnitude and orientation of dipole moment (favouring a non-flat conformer in the presence of an external electric field) due to a conformational change of one of the terminal MeS- groups. The results thus point to an intricate interplay between the applied bias voltage and the molecule dipole moment which could be the basis for designing new molecules aiming at controlling their conformation in devices.

Understanding the Molecule-Electrode Interface for Molecular Spintronic Devices: A Computational and Experimental Study.

A triple-decker SYML-Dy2 single-molecule magnet (SMM) was synthetized and grafted onto the surface of iron oxide nanoparticles (IO-NPs) coated by an oleic acid monolayer. The magnetism of the SYML-Dy2 complex, and the hybrid system, NP-Dy2, were studied by a superconducting quantum interference device (SQUID). Density functional theory (DFT) calculations were carried out to study both the energetics of the interaction between SYML-Dy2 complex to the organic capping, and the assembly presented by the oleic acid chains.

Effect of coordination geometry on the magnetic properties of a series of Ln2 and Ln4 hydroxo clusters.

A series of three isostructural tetranuclear complexes with the general molecular formula [Ln4(µ3-OH)4(L)4(µ2-piv)4(MeOH)4] (Ln = Gd 1, Dy 2 and Ho 3; LH = [1,3-bis(o-methoxyphenyl)-propane-1,3-dione]) were isolated and unambiguously characterized by single crystal XRD. Under similar reaction conditions, simply changing the co-ligand from pivalate to 2,6-bis(hydroxymethyl)-p-cresol (LH'3) led to the isolation of dinuclear Ln(iii) complexes with the general molecular formula [Ln2(L)4(µ2-LH'2)2]·4DMF (Ln = Gd 4, Dy 5 and Ho 6). Direct current magnetic susceptibility data studies on the polycrystalline sample of 1-6 and the results reveal the existence of weak antiferromagnetic exchange interactions between the lanthanide ions in 1 which is evident from the spin Hamiltonian (SH) parameters (J1 = -0.055 cm-1 and g = 2.01) extracted by fitting χMT(T). On the other hand, though complex 4 exhibits weak antiferromagnetic coupling (J1 = -0.048 cm-1 and g = 1.99) between the Gd(iii) ions, the χMT(T) data of complexes 5 and 6 unambiguously disclose the presence of ferromagnetic interactions between Dy(iii) and Tb(iii) ions at lower temperature. Magnetization relaxation dynamics studies performed on 2 show frequency dependent out-of-phase susceptibility signals in the presence of an optimum external magnetic field of 0.5 kOe. In contrast, complex 5 shows slow magnetization relaxation with an effective energy barrier (Ueff) of 38.17 cm-1 with a pre-exponential factor (τ0) of 1.85 × 10-6 s. The magnetocaloric effect (MCE) of complexes 1 and 4 was extracted from the detailed magnetization measurement and the change in the magnetic entropy (-ΔSm) of 1 and 4 was found to be 25.57 J kg-1 K-1 and 12.93 J kg-1 K-1, respectively, at 3.0 K for ΔH = 70 kOe.

Two Isostructural Coordination Polymers Showing Diverse Magnetic Behaviors: Weak Coupling (Ni(II)) and an Ordered Array of Single-Chain Magnets (Co(II)).

Two isomorphic 3-D complexes with the formulas [M3(TPTA) (OH)2(H2O)4]n (M = Ni for 1 and Co for 2; H4TPTA = [1,1':4',1″-terphenyl]-2',3,3″,5'-tetracarboxylic acid) have been synthesized and magnetically characterized. Complexes 1 (Ni(II)) and 2 (Co(II)) have the same 1-D rod-shaped inorganic SBUs but exhibit significantly different magnetic properties. Complex 2(Co(II)) is a 3-D arrangement of a 1-D Co(II) single-chain magnet (SCM), while complex 1(Ni(II)) exhibits weak coupling.

Multiscale study of mononuclear CoII SMMs based on curcuminoid ligands.

This work introduces a novel family of CoII species having a curcuminoid (CCMoid) ligand, 9Accm, attached, namely [Co(9Accm)2(py)2] (1) and [Co(9Accm)2(2,2'-bpy)] (2), achieved in high yields by the use of a microwave reactor, and exhibiting two different arrangements for the 9Accm ligands, described as "cis"(2) and "trans"(1). The study of the similarities/differences of the magnetic, luminescent and surface behaviors of the two new species, 1 and 2, is the main objective of the present work. The determined single-crystal structures of both compounds are the only CoII-CCMoid structures described in the literature so far. Both compounds exhibit large positive D values, that of 1 (D = +74 cm-1) being three times larger than that of 2 (D = +24 cm-1), and behave as mononuclear Single-Molecule Magnets (SMMs) in the presence of an external magnetic field. Their similar structures but different anisotropy and SMM characteristics provide, for the first time, deep insight on the spin-orbital effects thanks to the use of CASSCF/NEVPT2 calculations implementing such contributions. Further magnetic studies were performed in solution by means of paramagnetic 1H NMR, where both compounds (1 and 2) are stable in CDCl3 and display high symmetry. Paramagnetic NMR appears to be a useful diagnostic tool for the identification of such molecules in solution, where the resonance values found for the methine group (-CH-) of 9Accm vary significantly depending on the cis or trans disposition of the ligands. Fluorescence studies show that both systems display chelation enhancement of quenching (CHEQ) with regard to the free ligand, while 1 and 2 display similar quantum yields. Deposition of 1-2 on HOPG and Si(100) surfaces using spin-coating was studied using AFM; UV photoemission experiments under the same conditions display 2 as the most robust system. The measured occupied density of states of 2 with UV photoemission is in excellent agreement with theoretical DFT calculations.

Single-Crystal to Single-Crystal Linker Substitution, Linker Place Exchange, and Transmetalation Reactions in Interpenetrated Pillared-Bilayer Zinc(II) Metal-Organic Frameworks.

A twofold interpenetrated pillared-bilayer framework, {[Zn3 (L)2 (L2 )(DMF)]⋅(18DMF)(6H2 O)}n (1), has been synthesized from the ligands tris(4'-carboxybiphenyl)amine (H3 L) and 1,2-bis(4-pyridyl)ethylene (L2 ). The structure contains [Zn3 (COO)6 ] secondary building units (SBUs), in which three Zn(II) ions are almost linear with carboxylate bridging. This framework undergoes reversible pillar linker substitution reactions at the terminal Zn(II) centers with three different dipyridyl linkers of different lengths to afford three daughter frameworks, 2-4. Frameworks 2-4 are interconvertible through reversible linker substitution reactions. Also, competitive linker-exchange experiments show preferential incorporation of linker L3 in the parent framework 1. The larger linker L5 does not undergo such substitution reactions and framework 5, which contains this linker, can be synthesized solvothermally as a twofold interpenetrated structure. Interestingly, when framework 5 is dipped in a solution of L3 in DMF, linker substitution takes place as before, but linker L5 now moves and diagonally binds two Zn(II) centers to afford 6 as a nonpenetrated single framework. This linker place exchange reaction is unprecedented. All of these reactions take place in a single-crystal to single-crystal (SC-SC) manner, and have been observed directly through X-ray crystallography. In addition, each 3D framework undergoes complete copper(II) transmetalation.

Pentanuclear 3d-4f Heterometal Complexes of M(II)3Ln(III)2 (M = Ni, Cu, Zn and Ln = Nd, Gd, Tb) Combinations: Syntheses, Structures, Magnetism, and Photoluminescence Properties.

A new family of pentanuclear 3d-4f heterometal complexes of general composition [Ln(III)2(M(II)L)3(µ3-O)3H](ClO4)·xH2O (1-5) [Ln = Nd, M = Zn, 1; Nd, Ni, 2; Nd, Cu, 3; Gd, Cu, 4; Tb, Cu, 5] have been synthesized in moderate yields (50-60%) following a self-assembly reaction involving the hexadentate phenol-based ligand, viz., N,N-bis(2-hydroxy-3-methoxy-5-methylbenzyl)-N('),N(')-diethylethylenediamine (H2L). Single-crystal X-ray diffraction analyses have been used to characterize these complexes. The compounds are all isostructural, having a 3-fold axis of symmetry that passes through the 4f metal centers. The [M(II)L] units in these complexes are acting as bis-bidentate metalloligands and, together with µ3-oxido bridging ligands, complete the slightly distorted monocapped square antiprismatic nine-coordination environment around the 4f metal centers. The cationic complexes also contain a H(+) ion that occupies the central position at the 3-fold axis. Magnetic properties of the copper(II) complexes (3-5) show a changeover from antiferromagnetic in 3 to ferromagnetic 3d-4f interactions in 4 and 5. For the isotropic Cu(II)-Gd(III) compound 4, the simulation of magnetic data provides very weak Cu-Gd (J1 = 0.57 cm(-1)) and Gd-Gd exchange constants (J2 = 0.14 cm(-1)). Compound 4 is the only member of this triad, showing a tail of an out-of-phase signal in the ac susceptibility measurement. A large-spin ground state (S = 17/2) and a negative value of D (-0.12 cm(-1)) result in a very small barrier (8 cm(-1)) for this compound. Among the three Nd(III)2M(II)3 (M = Zn(II), Ni(II), and Cu(II)) complexes, only the Zn(II) analogue (1) displays an NIR luminescence due to the (4)F(3/2) → (4)I(11/2) transition in Nd(III) when excited at 290 nm. The rest of the compounds do not show such Nd(III)/Tb(III)-based emission. The paramagnetic Cu(II) and Ni(II) ions quench the fluorescence in 2-5 and thereby lower the population of the triplet state.