Synthesis and Spectroscopic Studies on Azo-Dye Derivatives of Polymetallic Lanthanide Complexes: Using Diazotization to Link Metal Complexes Together

Upconversion Luminescence with Bis-pyclen Yb(III) Chelates: Crown vs. Linear Polyether Linkers in Discrete Heteropolynuclear Architectures

Ligands combining two lateral bis-pyridyl-phosphonated-pyclens were synthesized, using a flexible linear pegylated linker (L2) or a bulkier K22 crown-ether (L3). A functionalized pyridyl-phosphonated-pyclen (L1) was also prepared as a mononuclear analogue. Coordination behavior of lanthanide cations was studied via NMR titration with Lu for L1, and UV/Vis and luminescence spectroscopy with Yb for L2/L3. Strong coordination of two Yb atoms enabled isolation and spectroscopic characterization of dinuclear complexes in H2O and D2O. Excited state lifetime analysis at 980 nm revealed strong protection of Yb cations, with no coordinated water molecule. Upon titration of the isolated dinuclear Yb complexes with Tb cations, cooperative upconversion (UC) sensitization of Tb in the visible was observed upon excitation of Yb at 980 nm in D2O. In the absence of Tb, the Yb complexes also exhibited cooperative luminescence with a weak emission band around 500 nm upon NIR Yb excitation. Efficient UC with Tb was only observed after thermal treatment, suggesting a slow kinetic of formation of the UC species. [Yb2TbL3] showed weak Tb centered UC emission, while the dinuclear complex of L2 displayed more intense UC emission up to two equivalents of Tb, forming [(Yb2L2)Tbx] (x=1-2), with the tetranuclear heterometallic complex being the most intense emitter. Log-Log plot analysis confirmed the two-photon nature of the UC process.

Energy exchange between Nd3+ and Er3+ centers within molecular complexes

Developing controlled and reproducible molecular assemblies incorporating lanthanide centers is a crucial step for driving forward up- and down-conversion processes. This challenge calls for the development of strategies to facilitate the efficient in situ segregation of different Ln metal ions into distinct positions within the molecule. The unique family of pure [LnLn'Ln] heterometallic coordination compounds previously developed by us represents an ideal platform for studying the desired Ln-to-Ln' energy transfer (ET). In this context, we report here the new pure one-step synthetically produced [ErNdEr] (3) complex, which allows for the first time at the molecular level to study the mechanisms behind Nd-to-Er energy transfer. To further assess the photophysical properties of this complex, the analogous [LuNdLu] (1) and [ErLaEr] (2) complexes have also been prepared and photophysically studied. Efficient sensitization via the two β-diketones employed as main ligands was probed for both Nd3+ and Er3+ ions, resulting in highly resolved emission spectra and sufficiently long excited state lifetimes, which allowed further assessment of the Ln-to-Ln' ET. This intermetallic transfer was first detected by comparing the emission spectra of iso-absorbant solutions and demonstrated by comparing the lifetime values with or without the lanthanide quencher (Er3+), as well as with a deep analysis of the excitation spectrum of the three complexes. Thus, a very unique phenomenon was discovered, consisting of a mutual Nd-to-Er and Er-to-Nd ET with no net increase of brightness by any metal; while Nd3+ transfers the energy received from the antenna to Er3+, the sensitization of the latter results in back-transfer to Nd3+ into a non-emissive, thus silent, state.

Programming heterometallic 4f-4f' helicates under thermodynamic control: the circle is complete

Three non-symmetrical segmental ligand strands L4 can be wrapped around a linear sequence of one Zn2+ and two trivalent lanthanide cations Ln3+ to give quantitatively directional [ZnLn2(L4)3]8+ triple-stranded helicates in the solid state and in solution. NMR speciations in CD3CN show negligible decomplexation at a millimolar concentration and the latter helicate can be thus safely considered as a preorganized C3-symmetrical HHH-[(L43Zn)(LnA)(2-n)(LnB)n]8+ platform in which the thermodynamic properties of (i) lanthanide permutation between the central N9 and the terminal N6O3 binding sites and (ii) exchange processes between homo- and heterolanthanide helicates are easy to access (Ln = La, Eu, Lu). Deviations from statistical distributions could be programmed by exploiting specific site recognition and intermetallic pair interactions. Considering the challenging La3+ : Eu3+ ionic pair, for which the sizes of the two cations differ by only 8%, a remarkable excess (70%) of the heterolanthanide is produced, together with a preference for the formation of the isomer where the largest lanthanum cation lies in the central N9 site ([(La)(Eu)] : [(Eu)(La)] = 9 : 1). This rare design and its rational programming pave the way for the preparation of directional light-converters and/or molecular Q-bits at the (supra)molecular level.

Distributive Nd-to-Yb Energy Transfer within Pure [YbNdYb] Heterometallic Molecules

Facile access to site-selective hetero-lanthanide molecules will open new avenues in the search of novel photophysical phenomena based on Ln-to-Ln' energy transfer (ET). This challenge demands strategies to segregate efficiently different Ln metal ions among different positions in a molecule. We report here the one-step synthesis and structure of a pure [YbNdYb] (1) coordination complex featuring short Yb···Nd distances, ideal to investigate a potential distributive (i.e., from one donor to two acceptors) intramolecular ET from one Nd³⁺ ion to two Yb³⁺ centers within a well-characterized molecule. The difference in ionic radius is the mechanism allowing to allocate selectively both types of metal ion within the molecular structure, exploited with the simultaneous use of two β-diketone-type ligands. To assist the photophysical investigation of this heterometallic species, the analogues [YbLaYb] (2) and [LuNdLu] (3) have also been prepared. Sensitization of Yb³⁺ and Nd³⁺ in the last two complexes, respectively, was observed, with remarkably long decay times, facilitating the determination of the Nd-to-Yb ET within the [YbNdYb] composite. This ET was demonstrated by comparing the emission of iso-absorbant solutions of 1, 2, and 3 and through lifetime determinations in solution and solid state. The comparatively high efficiency of this process corroborates the facilitating effect of having two acceptors for the nonradiative decay of Nd³⁺ created within the [YbNdYb] molecule.

Size Selectivity in Heterolanthanide Molecular Complexes with a Ditopic Ligand

The similar reactivity of lanthanides generally leads to statistically populated polynuclear complexes, making the rational design of ordered hetero-lanthanide compounds extremely challenging. Here we report on the site selectivity in hetero-lanthanide tetranuclear complexes afforded by the relatively simple ditopic pyterpyNO ligand (4'-(4-pyridil)-2,2':6',2"-terpyridine N-oxide). The sequential room temperature reaction of RE2 (tta)6 (pyterpyNO)2 (where RE=Y, (1); Eu, (2), Dy, (3) Htta=2-thenoyltrifluoroacetone) with La(tta)3 dme (dme=dimethoxyethane) yielded Y2 La2 (tta)12 (pyterpyNO)2 (4), Dy2 La2 (tta)12 (pyterpyNO)2 (5) and Eu2 La2 (tta)12 (pyterpyNO)2 (6). Single crystals X-ray diffraction studies showed that 4, 5 and 6 are isostructural, featuring a tetranuclear structure with two different metal coordination sites with coordination numbers 8 (CN8) and 9 (CN9). The two smaller cations are mainly bridged by the O-donor atoms of the NO groups of two pyterpyNO ligands (CN8), while the larger lanthanum centres are bound by a terpyridine unit (CN9). Size selectivity has been studied with structural and magnetic studies in the solid state and through 19 F NMR and photoluminescence studies in solution, showing a direct dependence on the difference of ionic radii of the ions and yielding a 91 % selectivity for 4. Furthermore, 19 F NMR, X-ray and PL studies pointed out that the nature of the product is independent from the synthetic route for compound Eu2 Y2 (tta)12 (pyterpyNO)2 (7), keeping the ion selectivity also for a self-assembly reaction. Unexpectedly, these studies have evidenced that selectivity is not exclusively governed by electrostatic interactions related to size dimensions.

Unparalleled selectivity and electronic structure of heterometallic [LnLn'Ln] molecules as 3-qubit quantum gates

Heterometallic lanthanide [LnLn'] coordination complexes that are accessible thermodynamically are very scarce because the metals of this series have very similar chemical behaviour. Trinuclear systems of this category have not been reported. A coordination chemistry scaffold has been shown to produce molecules of type [LnLn'Ln] of high purity, i.e. exhibiting high metal distribution ability, based on their differences in ionic radius. Through a detailed analysis of density functional theory (DFT) based calculations, we discern the energy contributions that lead to the unparalleled chemical selectivity of this molecular system. Some of the previously reported examples are compared here with the newly prepared member of this exotic list, [Er2Pr(LA)2(LB)2(py)(H2O)2](NO3) (1) (H2LA and H2LB are two β-diketone ligands). A magnetic analysis extracted from magnetization and calorimetry determinations identifies the necessary attributes for it to act as an addressable, conditional multiqubit spin-based quantum gate. Complementary ab initio calculations confirm the feasibility of these complexes as composite quantum gates, since they present well-isolated ground states with highly anisotropic and distinct g-tensors. The electronic structure of 1 has also been analyzed by EPR. Pulsed experiments have allowed the establishment of the quantum coherence of the transitions within the relevant spin states, as well as the feasibility of a coherent control of these states via nutation experiments.

Sorting Phenomena and Chirality Transfer in Fluoride-Bridged Macrocyclic Rare Earth Complexes

The reaction of fluoride anions with mononuclear lanthanide(III) and yttrium(III) hexaaza-macrocyclic complexes results in the formation of dinuclear fluoride-bridged complexes. As indicated by X-ray crystal structures, in these complexes two metal ions bound by the macrocycles are linked by two or three bridging fluoride anions, depending on the type of the macrocycle. In the case of the chiral hexaaza-macrocycle L1 derived from trans-1,2-diaminocyclohexane, the formation of these μ2-fluorido dinuclear complexes is accompanied by enantiomeric self-recognition of macrocyclic units. In contrast, this kind of recognition is not observed in the case of complexes of the chiral macrocycle L2 derived from 1,2-diphenylethylenediamine. The reaction of fluoride with a mixture of mononuclear complexes of L1 and L2, containing two different Ln(III) ions, results in narcissistic sorting of macrocyclic units. Conversely, a similar reaction involving mononuclear complexes of L1 and complexes of achiral macrocycle L3 based on ethylenediamine results in sociable sorting of macrocyclic units and preferable formation of heterodinuclear complexes. In addition, formation of these heterodinuclear complexes is accompanied by chirality transfer from the chiral macrocycle L1 to the achiral macrocycle L3 as indicated by CPL and CD spectra.

Designed polynuclear lanthanide complexes for quantum information processing

The design of dissymmetric organic ligands featuring combinations of 1,3-diketone and 2,6-diacetylpyridine coordination pockets has been exploited to produce dinuclear and trinuclear lanthanide-based coordination compounds. These molecules exhibit two or more non-equivalent Ln ions, most remarkably enabling the access to well-defined heterolanthanide compositions. The site-selective disposition of each metal ion within the molecular entities allows the study of each centre individually as a spin-based quantum bit, affording unparalleled versatility for quantum gate design. The inherent weak interaction between the Ln ions permits the performance of multi-qubit quantum logical operations realized through their derived magnetic states, or implementing quantum-error correction protocols. The different studies performed to date on these systems are revised, showing their vast potential within spin-based quantum information processing.

Accessing Lanthanide-to-Lanthanide Energy Transfer in a Family of Site-Resolved [LnIII LnIII '] Heterodimetallic Complexes

The ligand H₃ L (6-[3-oxo-3-(2-hydroxyphenyl)propionyl]pyridine-2-carboxylic acid), which exhibits two different coordination pockets, has been exploited to engender and study energy transfer (ET) in two dinuclear [Ln^III Ln^III '] analogues of interest, [EuYb] and [NdYb]. Their structural and physical properties have been compared with newly synthesised analogues featuring no possible ET ([EuLu], [NdLu], and [GdYb]) and with the corresponding homometallic [EuEu] and [NdNd] analogues, which have been previously reported. Photophysical data suggest that ET between Eu^III and Yb^III does not occur to a significant extent, whereas emission from Yb^III originates from sensitisation of the ligand. In contrast, energy migration seems to be occurring between the two Nd^III centres in [NdNd], as well as in [NdYb], in which Yb^III luminescence is thus, in part, sensitised by ET from Nd. This study shows the versatility of this molecular platform to further the investigation of lanthanide-to-lanthanide ET phenomena in defined molecular systems.

Design and Synthesis of Luminescent Lanthanide-Based Bimodal Nanoprobes for Dual Magnetic Resonance (MR) and Optical Imaging

Current biomedical imaging techniques are crucial for the diagnosis of various diseases. Each imaging technique uses specific probes that, although each one has its own merits, do not encompass all the functionalities required for comprehensive imaging (sensitivity, non-invasiveness, etc.). Bimodal imaging methods are therefore rapidly becoming an important topic in advanced healthcare. This bimodality can be achieved by successive image acquisitions involving different and independent probes, one for each mode, with the risk of artifacts. It can be also achieved simultaneously by using a single probe combining a complete set of physical and chemical characteristics, in order to record complementary views of the same biological object at the same time. In this scenario, and focusing on bimodal magnetic resonance imaging (MRI) and optical imaging (OI), probes can be engineered by the attachment, more or less covalently, of a contrast agent (CA) to an organic or inorganic dye, or by designing single objects containing both the optical emitter and MRI-active dipole. If in the first type of system, there is frequent concern that at some point the dye may dissociate from the magnetic dipole, it may not in the second type. This review aims to present a summary of current activity relating to this kind of dual probes, with a special emphasis on lanthanide-based luminescent nano-objects.

Macrocyclic Chelates Bridged by a Diaza-Crown Ether: Towards Multinuclear Bimodal Molecular Imaging Probes

Bridged polymacrocyclic ligands featured by structurally different cages offer the possibility of coordinating multiple trivalent lanthanide ions, giving rise to the exploitation of their different physicochemical properties, e.g., multimodal detection for molecular imaging purposes. Intrigued by the complementary properties of optical and MR-based image capturing modalities, we report the synthesis and characterization of the polymetallic Ln(III)-based chelate comprised of two DOTA-amide-based ligands (DOTA—1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) bridged via 1,10-diaza-18-crown-6 (DA18C6) motif. The DOTA-amide moieties and the DA18C6 were used to chelate two Eu(III) ions and one Tb(III) ion, respectively, resulting in a multinuclear heterometallic complex Eu₂LTb. The bimetallic complex without Tb(III), Eu₂L, displayed a strong paramagnetic chemical exchange saturation transfer (paraCEST) effect. Notably, the luminescence spectra of Eu₂LTb featured mixed emission including the characteristic bands of Eu(III) and Tb(III). The advantageous features of the complex Eu₂LTb opens new possibilities for the future design of bimodal probes and their potential applicability in CEST MR and optical imaging.

Direct solid-phase synthesis of molecular heterooligonuclear lanthanoid-complexes

Molecular lanthanoid complexes are highly valuable building blocks for a number of important technological applications, e.g. as contrast agents in magnetic resonance imaging (MRI) or as luminescent probes for bioassays. For the next generation of advanced applications based on molecular species, heterooligonuclear lanthanoid complexes with well-defined chemical and structural compositions are required. The great kinetic lability of trivalent lanthanoids so far prevents the realization of such molecular architectures with a universally applicable methodology. Here, we have developed functionalized molecular lanthanoid cryptates as monomeric building blocks which can be directly linked by standard solid-phase peptide synthesis to yield sequence-specific heterooligonuclear lanthanoid complexes. These molecular materials enable unique applications such as the generation of molecular codes with very convenient luminescence read-out.

Near-infrared emitting lanthanide(iii) complexes as prototypes of optical imaging agents with peptide targeting ability: a methodological approach

A methodological approach to design prototypes of specific near-infrared emitting imaging agents based on a small molecular compound combining a lanthanide(iii) ion, the cyclen derivative as a coordinating unit and the azo-dye as a sensitizer with a Arg-Gly-Asp cyclopeptide as a targeting moiety, is presented here.

NIR Ln(iii) complexes combining a cyclen derivative, azo-dye as a sensitizer and a cRGD peptide as a targeting moiety.

Multimetallic Lanthanide Complexes: Using Kinetic Control To Define Complex Multimetallic Arrays

Kinetically inert lanthanide complexes are proving to be highly effective building blocks for the preparation of complex heterometallic architectures, allowing complete control of metal ion domains, which cannot be achieved under thermodynamic control. Kinetic stability may render perceivable labile coordination bonds more durable than several types of covalent interactions. For complexes in clinical use, the significance of kinetic stability cannot be overstated, and this Account treats the topic accordingly. Kinetically inert complexes can be used as building blocks for elaborate synthesis. For instance, it is now possible to prepare heterometallic lanthanide complexes containing two or more different lanthanide ions by linking kinetically robust complexes together. This approach can yield bimetallic (f-f' or d-f) and trimetallic (f-f'-f″) lanthanide complexes. In this Account, we describe our studies exploiting the slow dissociation of lanthanide complexes derived from 1,4,7,10-tetraazadodecane-1,4,7,10-tetraacetic acid (DOTA) related ligands to link complexes together through synthetic manipulation of pendent groups on the ligand skeleton or through coordination of bridging donor groups to a d-block metal center. In the course of this work, we have developed a variety of such methods, ranging from peptide coupling and diazotization to Ugi and click chemistry and have also explored the use of alternative strategies that combine orthogonal protecting group chemistry with sequential complexation of different lanthanide ions or that use self-assembly to deliver well-defined multimetallic systems. These well-defined bimetallic systems also have considerable scope for exploitation. Since the earliest studies, it has been clear that there is potential for application in the burgeoning field of molecular imaging. Heterometallic lanthanide complexes can be used as single-molecule bimodal imaging agents through incorporation of MRI active and luminescent components. Alternatively, conventional luminescence methods can be exploited in conjunction with lanthanide luminescence. In the simplest cases, a single lanthanide can be used to achieve a switchable response in combination with a transition metal complex. Bimetallic f-f' complexes allow the full potential of the approach to be realized in systems in which one lanthanide responds to changes in the concentration of an analyte, while a second lanthanide center can be used to define the concentration of the probe itself. This offers a new solution to the old dichotomy of ratiometric imaging that can potentially be applied widely.

Selective Lanthanide Distribution within a Comprehensive Series of Heterometallic [LnPr] Complexes

The preparation of heterometallic, lanthanide-only complexes is an extremely difficult synthetic challenge. By a ligand-based strategy, a complete isostructural series of dinuclear heterometallic [LnPr] complexes has been synthesized and structurally characterized. The two different coordination sites featured in this molecular entity allow study of the preferences of the praseodymium ion for a specific position depending on the ionic radii of the accompanying lanthanide partner. The purity of each heterometallic moiety has been evaluated in the solid state and in solution by means of crystallographic and spectrometric methods, respectively, revealing the limits of this strategy for ions with similar sizes. DFT calculations have been carried out to support the experimental results, confirming the nature of the site-selective lanthanide distribution. The predictable selectivity of this system has been exploited to assess the magnetic properties of the [DyPr] and [LuPr] derivatives, showing that the origin of the slow dynamics observed in the former arises from the dysprosium ion.

Composed in the f-block: solution structure and function of kinetically inert lanthanide(iii) complexes

An induction to the wonders of lanthanides, and a call for standardised methods for characterisation of lanthanide complexes in solution.

Luminescence of a binuclear europium complex bearing a 4-nitrophenolate chromophore: a different way of seeing pH dependence

A europium complex derived from NP-(DO3A)₂ exhibits pH-dependent europium-centred luminescence following excitation of the nitrophenolate chromophore.

Tailoring functionality through synthetic strategy in heterolanthanide assemblies

Three classes of heterolanthanide assemblies, multi-dimensional frameworks (A), discrete polynuclear molecules (B) and preformed coordinated units connected by a linker (C), are discussed. Potential functionalities arising from the distance-dependent coexistence or interplay of the physical properties are pointed out.

Syntheses, structures and properties of 5-azotetrazolyl salicylic acid and its dilanthanide complexes

Two hydrated 5-azotetrazolyl salicylic acids (H₃ASA) and five H₃ASA based dinuclear Ln³⁺ complexes have been synthesized and characterized by single crystal X-ray diffraction analysis.

Towards polymetallic lanthanide complexes as dual contrast agents for magnetic resonance and optical imaging

In the spotlight: polymetallic complexes permitting efficient sensitization of lanthanide luminescence and exhibiting favorable relaxometric properties.

Using remote substituents to control solution structure and anion binding in lanthanide complexes

A study of the anion-binding properties of three structurally related lanthanide complexes, which all contain chemically identical anion-binding motifs, has revealed dramatic differences in their anion affinity. These arise as a consequence of changes in the substitution pattern on the periphery of the molecule, at a substantial distance from the binding pocket. Herein, we explore these remote substituent effects and explain the observed behaviour through discussion of the way in which remote substituents can influence and control the global structure of a molecule through their demands upon conformational space. Peripheral modifications to a binuclear lanthanide motif derived from α,α'-bis(DO3 Ayl)-m-xylene are shown to result in dramatic changes to the binding constant for isophthalate. In this system, the parent compound displays considerable conformational flexibility, yet can be assumed to bind to isophthalate through a well-defined conformer. Addition of steric bulk remote from the binding site restricts conformational mobility, giving rise to an increase in binding constant on entropic grounds as long as the ideal binding conformation is not excluded from the available range of conformers.

Metal-controlled diastereoselective self-assembly and circularly polarized luminescence of a chiral heptanuclear europium wheel

The chiral dissymmetric tetradentate ligand (S)-6'-(4-phenyloxazolin-2-yl)-2,2'-bipyridine-6-carboxylate (S-Phbipox) leads to the diastereoselective assembly of a homochiral Eu(3+) triangle and a highly emissive (quantum yield = 27%) heptanuclear wheel that is the largest example of a chiral luminescent complex of Eu(3+) reported to date. The nuclearity of the assembly is controlled by the solvent and the Eu(3+) cation. All of the compounds show large circularly polarized luminescence with an activity that varies with the nature of the assembly (highest for the homochiral trimer).

Self-assembly between dicarboxylate ions and a binuclear europium complex: formation of stable adducts and heterometallic lanthanide complexes

A binuclear lanthanide complex consisting of two lanthanide binding domains linked by a m-xylyl bridging unit forms very stable 1 : 1 adducts with benzene dicarboxylic acids and their derivatives. The complex with isophthalate derivatives is particularly stable.

Photophysical approaches to responsive optical probes

Responsive optical probes play a vital role in following and understanding biological events. In this review, we focus on the use of lanthanide complexes as molecular probes, as they offer many advantages in imaging and assays, particularly when used in time-gated protocols. We describe systems that illustrate the key photophysical approaches to achieving analyte-dependent signal modulation. In summary, this signal modulation can be achieved through changes either in the coordination sphere of the lanthanide or in the pathway of sensitized emission. In conclusion, we describe the main challenges to be overcome in the field of responsive probes, mainly the effective determination of concentrations in vivo and the development of probes with temporal responses adequate to follow fast processes.

Enantiomeric self-recognition in homo- and heterodinuclear macrocyclic lanthanide(III) complexes

The controlled formation of lanthanide(III) dinuclear μ-hydroxo-bridged [Ln(2)L(2)(μ-OH)(2)X(2)](n+) complexes (where X = H(2)O, NO(3)(-), or Cl(-)) of the enantiopure chiral macrocycle L is reported. The (1)H and (13)C NMR resonances of these complexes have been assigned on the basis of COSY, NOESY, TOCSY, and HMQC spectra. The observed NOE connectivities confirm that the dimeric solid-state structure is retained in solution. The enantiomeric nature of the obtained chiral complexes and binding of hydroxide anions are reflected in their CD spectra. The formation of the dimeric complexes is accompanied by a complete enantiomeric self-recognition of the chiral macrocyclic units. The reaction of NaOH with a mixture of two different mononuclear lanthanide(III) complexes, [Ln(1)L](3+) and [Ln(2)L](3+), results in formation of the heterodinuclear [Ln(1)Ln(2)L(2)(μ-OH)(2)X(2)](n+) complexes as well as the corresponding homodinuclear complexes. The formation of the heterodinuclear complex is directly confirmed by the NOESY spectra of [EuLuL(2)(μ-OH)(2)(H(2)O)(2)](4+), which reveal close contacts between the macrocyclic unit containing the Eu(III) ion and the macrocyclic unit containing the Lu(III) ion. While the relative amounts of homo- and heterodinuclear complexes are statistical for the two lanthanide(III) ions of similar radii, a clear preference for the formation of heterodinuclear species is observed when the two mononuclear complexes contain lanthanide(III) ions of markedly different sizes, e.g., La(III) and Yb(III). The formation of heterodinuclear complexes is accompanied by the self-sorting of the chiral macrocyclic units based on their chirality. The reactions of NaOH with a pair of homochiral or racemic mononuclear complexes, [Ln(1)L(RRRR)](3+)/[Ln(2)L(RRRR)](3+), [Ln(1)L(SSSS)](3+)/[Ln(2)L(SSSS)](3+), or [Ln(1)L(rac)](3+)/[Ln(2)L(rac)](3+), results in mixtures of homochiral, homodinuclear and homochiral, heterodinuclear complexes. On the contrary, no heterochiral, heterodinuclear complexes [Ln(1)L(RRRR)Ln(2)L(SSSS)(μ-OH)(2)X(2)](n+) are formed in the reactions of two different mononuclear complexes of opposite chirality.