DINUCLEAR COMPLEXES AS BUILDING BLOCKS FOR TETRA-NUCLEAR MACROCYCLIC COMPLEXES WITH DITHIOLATE MACROCYCLIC LIGAND

A series of novel tri-, tetraand pentanuclear complexes composed of dinuclear LM2 units (M=Co, Ni, Zn; L=24-membered macrocyclic hexaaza-dithiophenolate ligand) and ferrocene-carboxylate ([CpFeC5H4CO2]ˉ), 1,1’-ferro-cenedicarboxylate([Fe(C5H4-CO2)2] 2ˉ), acetylenedicarboxylate, terephthalate, isophthalate, and naphthalene diimide dicar-boxylate groups is reported. The complexes have been synthesized and characterised by UV/Vis-, IR-spectroscopy, and X-ray crystallography. Each dicarboxylate dianion acts as a quadridentate bridging ligand linking two bioctahedral LM2 units via μ1,3-bridging carboxylate functions to generate discrete dications with a central LM2(O2C-R-CO2)M2L core.


Introduction
The chemistry of container molecules has developed extensively over the past two decades.Many container molecules such as calixarenes, resorcarenes, cyclodextrins, carcerands and glycourils have been invaluable in studying the fundamental principles of inclusion phenomena and consequently their use in separation science or drug delivery, as two examples of application.Importantly, the area has attracted interest in the field of supramolecular chemistry because the properties of such host-guest compounds are often different from those of their constituent components.By adjusting the size and form of the binding cavity it is often possible to complex co-ligands in unusual coordination modes, to activate and transform small molecules, or to stabilize reactive intermediates [1,2].One subclass are the metallated container molecules, in which metal ions and clusters are used as both a point of recognition and to give the container a well-defined structure.Such compounds also allow for an interplay of molecular recognition and transition-metal catalysis, and for the construction of more effective enzyme mimics.Of interest to the present work is the ability of metallocavitands to recognize and encapsulate difunctionalised molecules towards stabilising or enhancing the optical and electronic properties of redox-and photo-active compounds within a confined environment set up by two hemispheres.

Dicarboxylate dianions as a tetradentate bridged ligands.
In view of the increasing interest in the targeted assembly of molecular-based magnetic materials using high-spin molecules of higher nuclearity [30][31][32][33][34][35][36], we considered it worthwhile to examine the possibility of linking pairs of dinuclear [LNi II  2 ] units by dicarboxylate dianions to form tetranuclear species.In the present contribution we report the synthesis and crystallographic characterization of three tetranuclear nickel (II) complexes of the type [LNi II 2 dicarboxylateNi II 2 L], where "dicarboxylate" stands for acetylenedicarboxylate, terephthalate, or isophthalate dianions.A schematic representation of these complexes is shown in Scheme 2. These complexes differ by the distance between the centre of the Ni•••Ni axis of the isostructural LNi 2 subunits, their relative orientation, and the nature of the bridging ligands.The ability of the dicarboxylate dianions to mediate magnetic exchange interactions between the dinuclear subunits is examined and discussed in the light of their specifi c structural features.g p Scheme 2. Complexes prepared and their labels.
Nonetheless, linking of two [LNi 2 ] 2+ fragments by the carboxylato ligands is a clean and facile step driven by the low solubility of the products.

[(LNi II
2 ) 2 (acetylenedicarboxylate)] 2+ All compounds gave satisfactory elemental analyses and their IR spectra are marked by the prominent asymmetric and symmetric carboxylate stretching frequencies around 1580 cm -1 and 1420 cm -1 , diagnostic of μ 1,3 -bridging carboxylate functions [38].The UV/Vis spectra of 6-8 in acetonitrile display two weak bands above 500 nm typical of octahedral Ni 2+ (d 8 , S = 1) ions.The observed values compare closely with those of the acetato-bridged complex [LNi II 2 (OAc)] + [29], indicative of a pseudo-octahedral N 3 S 2 O coordination environment about the metal ions.This is confi rmed by single-crystal X-ray crystallography.The acetylenedicarboxylate dianion acts as a tetradentate bridging ligand joining two dinuclear [LNi II 2 ] 2+ fragments through its carboxylate functions to give a tetranuclear Ni 2 -(O 2 CC≡CCO 2 )-Ni 2 array.Each nickel atom is surrounded in a highly distorted octahedral fashion by two sulfur atoms and three nitrogen atoms from the supporting ligand, and one oxygen atom from the acetylenedicarboxylate moiety.The Ni 2 carboxylato planes are necessarily twisted by 86.3° about the C≡C bond to relieve the unfavourable steric interactions between the bulky tBu groups of the two opposing [LNi II  2 ] 2+ subunits.The coligand is also slightly bent (C≡C 1.185( 6) Ǻ) such that the intramolecular distances between two nickel atoms of different dinuclear subunits within the tetranuclear complex range from 8.623(1) to 9.769(1) Å.The only system comparable to that of 6 is provided by the complex [{Mo 2 (DAniF) 3 } 2 (O 2 CC≡CCO 2 )], where DAniF = N,N'-di-p-anisylformamidinate, for which an intramolecular Mo•••Mo distance of 9.537 Å has been reported [39].There are no signifi cant intermolecular interactions between the Ni II  4 complexes within the lattice.The shortest intermolecular Ni•••Ni distance is at 7.470(1) Å.
Figure 2 shows the structure of the tetranuclear nickel(II) complex 7 in crystals of  The isophthalate dianion is bonded to two [LNi II 2 ] 2+ units through μ 1,3 -bridging carboxylate functions.The metalligand bond lengths within 8 reveal no anomalities and are very similar to those in 6 and 7. Strangely, the twisting of the carboxylato planes is less pronounced than in the previous cases.In fact, the two planes are almost coplanar with the phenyl ring of the bridging isophthalate dianion.The geometrical requirements of the isophthalate moiety with the two carboxylate functions in meta orientation leads to a distance of 9.561 Å between the center of the Ni•••Ni axes of the dinuclear units.This value should be compared with that of 10.712 Å in 7, where the two carboxylate functions are in para positions.The present coordination mode of the isophthalate dianion forming a discrete Ni II  4 cluster is without precedence in the literature [42][43][44].
The magnetic properties of the three carboxylato-bridged complexes were examined in view of literature reports that conjugated dicarboxylate ligands are able to mediate long-range magnetic exchange interactions between paramagnetic metal ions [45].The variable-temperature magnetic susceptibility data for 6[BPh 4 ] 2 , 7[BPh 4 ] 2 , and 8[BPh 4 ] 2 were measured over the range 2.0-295 K using a SQUID magnetometer and an applied external magnetic fi eld of 0.2 T. Plots of the temperature dependence of the effective magnetic moment for μ eff the three compounds are shown in In all cases the maximum value of the effective magnetic moment is lower than expected for a spin-only value of 9.84 μ B for S T = 4 resulting from ferromagnetic coupling of four Ni II (S i = 1, g = 2.20) ions.However, the values are also signifi cantly larger than the value of 6.22 μ B calculated for completely uncoupled spins.The overall behaviour indicates the presence of weak ferromagnetic exchange interactions between the Ni 2+ ions within the dinuclear subunits, but negligible, if any, coupling across the dicarboxylate bridges.The latter behaviour can be attributed to the long distance between the Ni 2+ ions spanned by the dicarboxylates.In this regard, it is worthwhile noting that very weak exchange interactions have indeed been reported for other terephthalato-or isophthalato-bridged nickel(II) complexes [28,46,47].
In summary, all three new compounds are discrete tetranuclear nickel(II) complexes composed of pairs of bioctahedral [LNi II  2 ] 2+ units united by a tetradentate dicarboxylate anion.The calixarene-like conformation adopted by the supporting ligand leads to an almost complete encapsulation of the Ni 2 (O 2 C-R-CO 2 )Ni 2 core.As a consequence the Ni II  4 clusters are well-separated from each other in the solid state, featuring only intermolecular van der Waals contacts.

Redox-active ferrocenecarboxylates anions coordinated by dinuclear aminethiolate complexes
Polynuclear complexes composed of classical and organometallic complex fragments have attracted considerable attention in recent years [48,49], owing to their rich redox chemistry [50, 51], the search for novel magnetic and electronic materials [52,53], and potential applications in catalysis [51].In addition, the presence of redox-active signalling groups and open coordination sites enables these compounds to be used as selective sensor molecules for target guest species [54][55][56][57][58][59].So far, research in this area has mainly focused on conjugates built up of mononuclear LM complexes (L = chelate ligand) and suitably functionalized ferrocene derivatives [60][61][62][63].Less attention has been paid to the use of discrete dinuclear LM 2 building blocks.The tetranuclear Mo 4 complexes containing two quadruply bonded Mo 2 -formamidinate units linked by 1,1'-ferrocenedicarboxylate dianions may serve as rather rare examples of this class of compounds [64].
We have also been able to isolate the two-electron-oxidized Co II Co III form 14[ClO 4 ] 4 of compound 12[ClO 4 ] 2 .This mixed-valent complex was prepared as a black powder in good yields by oxidation of 12[ClO 4 ] 2 with 1 equiv of bromine in acetonitrile at 0 o C followed by addition of a saturated ethanol solution of LiClO 4 and low-temperature vacuum concentration.In contrast to 12[ClO 4 ] 2 , 14[ClO 4 ] 4 exhibits excellent solubility in acetonitrile.Such solutions can be stored for several days at ambient temperature without noticeable decomposition.Attempts to prepare the analogous [(LNi II Ni III ) 2 (μ-O 2 CC 5 H 4 ) 2 Fe] 4+ complex were not successful.
All compounds gave satisfactory elemental analyses and were characterized by appropriate spectroscopic methods (IR, NMR, UV/Vis -spectroscopy).The infrared spectra of the new complexes display absorptions due to the [LM 2 ] 2+ fragments, the counter ions (ClO 4 ‾ or BPh 4 ‾), and the ferrocene derivatives.The ferrocene-carboxylates in 9-13 give rise to two characteristic bands, as in other carboxylato-complexes [38,77], in the 1575-1565 cm‾ 1 and 1435-1425 cm‾ 1 ranges; these are assigned to the asymmetric and symmetric carboxylate stretching modes, respectively.These values are very similar to those in 3-5 indicative of μ 1,3 -bridging carboxylate functions [69,70].The oxidation of 12 to 14 is accompanied by a shift of the asymmetric stretching mode by ≈ 18 cm‾ 1 to lower wavenumbers.A similar behaviour was observed for the acetato-bridged Co II 2 complex 4 [70].The data are thus in good agreement with the formulation of complex 14 as a mixed-valent Co II Co III species.
The diamagnetic Zn 2 Fe complex 11 was characterized by NMR spectroscopy to determine its structure in solution.The UV/Vis spectra of 9, 10, 12, and 13 display several weak bands above 500 nm typical of octahedral high-spin Co II (d 7 , S = 3 / 2 ) and Ni II (d 8 , S=1) ions, respectively.The observed values closely compare with those of 4 and 5 again consistent with pseudo-octahedral N 3 S 2 O coordination environments around the metal atoms [69,70].For the Zn 2 Fe species 11[ClO 4 ] two absorptions bands are detected at 342 and 440 nm; these are readily assigned to the d-d transitions of the coordinated [CpFe(C 5 H 4 CO 2 )]‾ unit.The feature at 440 nm is also evident in the electronic absorption spectrum of the Ni 2 Fe complex 10.In the UV spectrum of 11, this band is obscured by an intense ligand-to-metal charge-transfer transition (RS→Co II ).The d-d transitions of the [Fe(η 5 -C 5 H 4 CO 2 )] 2 ‾ unit in 12, 13 and 14 could not be located.
The UV/Vis spectrum of the mixed-valent Co II Co III complex 14 is dominated by two very intense absorptions at ≈ 449 and 681 nm; these are attributable to RS→Co III charge-transfer transitions.Such intense LMCT transitions are characteristic of thiolato-bridged Co II Co III complexes.The corresponding absorptions in [LCo II Co III (μ-OAc)] 2+ , for example, were observed at 460 and 710 nm [70].It should be noted that the UV/Vis spectrum of 14 reveals no bands attributable to intervalence transfer (IT) bands.Complex 14 is therefore presumably class I in Robin and DayOs classifi cation of mixed-valence species with distinct localized high-spin Co II and low-spin Co III sites [82].This is confi rmed by the crystal structure determination of  3), and 2.517(1) Å, respectively.Virtually the same distances are seen in the acetato-bridged complex 4 [67].A large number of metal complexes containing ferrocenecarboxylate ligands have been structurally characterized [84][85][86]; to our knowledge, 9 is the fi rst such complex supported by a dinuclear aminethiolate metallo ligand.
In contrast to the compound above, 10[BPh 4 ] recrystallized from acetonitrile/ethanol 1:1 with only one acetonitrile solvate molecule.Figure 6 shows the ferrocenecarboxylate to be coordinated to the [LNi II  2 ] unit in a manner identical to the situation found in 9 (Figure 5).The two compounds were found to be isomorphous in spite of differences in the number and type of solvate molecules.The following discussion will focus on the Co 4 II Fe complex 12. Metrical details for the Ni 4 II Fe complex 13 are reported in square brackets.
As can be seen in Figure 7b  Evidently, the crystal structures of 12-14 clearly show that dinuclear LM 2 units can be coupled together by the 1,1'-ferrocendicarboxylate dianion.Moreover, the pentanuclear Co 4 Fe complex 12 is even accessible in another oxidation state.The oxidation is metal-centered and occurs without gross structural changes of the parent complex 12.This fi nding paves the way for novel multi-redox systems composed of binuclear complex units and multifunctional metalorganic linkers which may fi nd applications due to novel chemical or physico-chemical properties that are not seen for the individual components [91].
One facet of the present complexes is the presence of a redox-active ferrocene unit in close proximity to one or two redox-active [LM 2 ] 2+ groups.This feature suggests that electron transfer events can infl uence one another owing to the short distance (5.6±0.2Å) between the redox centres.To determine whether this is the case, cyclovoltammetric studies have been carried out on the M 2 Fe complexes 9[ClO 4 ]-11[ClO 4 ] and the Co 4 Fe compound 14[ClO 4 ] 4 .The cyclic voltammograms (CV's) have been recorded in acetonitrile solution with tetra-n-butylammonium hexafl uorophosphate as the supporting electrolyte.The electrochemical results are shown in Figure 9, and the redox potentials referenced versus SCE are collected in Table 1.   [9 aq.CH 3 CN CH 3 CN 0,53 0,63(50) [CpFe(C 5 H 4 CO 2 )] -[c] [91]  aq.CH 3 CN CH 3 CN 0,34 0,44 [CpFe(C 5 H 4 CO 2 H) 2 ] DMF 0,80(0.10) [a] The CV's were recorded at ambient temperature using 0.10 M [ n Bu 4 N][PF 6 ] as supporting electrolyte at a scan rate of 100 mV s -1 .
The data refer to the perchlorate salts.Sample concentration was ca.1.0x10 -3 M. All potentials are referenced versus the saturated calomel electrode (SCE). [b] Separation between the anodic (E pa ) and cathodic peaks (E pc ) of the redox wave (∆E p =E pa -E pc ). [c] Sodium salt. [d] Peak-potential value for irreversible processes.
The electrochemical data of 3-5, ferrocenecarboxylic acid and 1,1'-ferrocenedicarboxylic acid have been included for comparative purposes [92].The CV of the Zn 2 Fe complex 11[ClO 4 ] shows one reversible redox wave at +0.54 V that can be readily assigned to the oxidation of the ferrocene moiety, since it its absent in the CV of [LZn 2 (OAc)] [ClO 4 ] (3[ClO 4 ]).Interestingly, the complexation of [CpFe(C 5 H 4 COO)]‾ causes an anodic potential shift of 90 mV in the reversible redox wave of the ferrocene moiety.It is assumed that this potential shift results from the electrostatic repulsion (Coulomb) effect between the two Zn 2+ ions bonded by the macrocycle and the positively charged ferrocenium centre.Thus complexation of [CpFe(C 5 H 4 COO)]‾ by the dipositively charged [LZn 2 ] 2+ unit makes the ferrocenyl group more diffi cult to oxidize.Curiously, an anodic shift of ≈ 140 mV for the peak potential for the second, irreversible ligandbased oxidation (formally a RS‾→RS • transition) [29] that follows the ferrocenyl centred oxidation is also evident.In this case it is the additional positive charge on the ferrocene that causes the thiolate sulfur atoms to be oxidized at a higher potential.The redox-processes for 11 3+  11 2+  11 + (=11) 14 6+  14 4+  14 2+ (=14)

Scheme 5. Assignment of redox processes in 9-11 and 14
The CV of the Co 2 Fe complex 9 exhibits three reversible one-electron redox waves which can be assigned to i) a metal-centered Co II   The potential shift for the oxidation of the ferrocenyl unit in 9 3+ (∆E = +0.37V) is signifi cantly larger than in 11 + .The signifi cantly larger shift is likely to be a result of the higher positive charge of the [LCo III 2 ] 5+ fragment to which the Fe II (Cp)(C 5 H 4 COO‾) unit is attached in 9 3+ .The CV of Ni 2 Fe compound 10 reveals two electrochemically reversible and one irreversible redox waves, which by comparison with the CV of 5 [29] are tentatively assigned to i) a metal-centred Ni II Ni II →Ni II Ni III oxidation yielding the mixed-valent dication [LNi III Ni II (O 2 CC 5 H 4 Fe II Cp)] 2+ (5 2+ ) at 0.53 V, ii) the oxidation of the metal organic unit forming [LNi III Ni II (O 2 CC 5 H 4 Fe III Cp)] 3+ (5 3+ ) at 0.71 V, and iii) the oxidation of the thiophenolate sulfur atoms yielding a nickel bound thiyl radical at 1.59 V. Anodic shifts in the second and third redox waves are clearly discernible, confi rming the above fi ndings that the electron transfer events of the ferrocenyl moiety and the binuclear subunit infl uence one another.The fact that the potential shifts are not so pronounced than in 9 is in good agreement with the smaller positive charges of the participating species.It should be noted that all oxidation products of 9 and 10 are only stable on the time scale of a cyclic voltammetry experiment.Attempts to prepare these compounds by electrochemical or chemical oxidation led to unidentifi ed decomposition products.Thus, while some of the above oxidations appear electrochemically reversible, they are all chemically irreversible.
Of the tetranuclear complexes, only complex 14[ClO 4 ] 4 had suffi cient solubility (due to its higher charge) to examine its electrochemical properties by cyclic voltammetry.The CV shows two quasi-reversible redox waves.On the basis of the crystal structure of 14[ClO 4 ] 4 , the fi rst redox wave at 0.22 V can be assigned to a two-electron reduction of 14 4+ yielding the fully-reduced Co II  4 Fe form 14 2+ (which is assumed to be identical with 12).The other wave at 0.53 V can be attributed to a metal-centred two-electron oxidation process yielding the fully oxidized Co III   4   Fe form [(LCo III 2 ) 2 (Fe(Cp))] 6+ (14 6+ ).The observed potential values are almost identical with those in 4 [67], indicating that the oxidation/ reduction processes at one [LCo 2 ] unit do not infl uence the ones that occur at the other.In other words, the two dinuclear cobalt(II) subunits behave as two independent redox-groups.That is fully consistent with the large distance between the two subunits and the fact that the electrostatic (Coulomb) interactions decrease rapidly with increasing distance between the redox sites.The redox wave for the oxidation of the [Fe(C 5 H 4 CO 2 ) 2 ] 2 ‾ unit in 14 could not be detected.We assume that it is obscured by the redox waves at 0.53 V.
There have been many reports in the literature that a charged subunit can infl uence the redox properties of an adjacent ferrocene group [93] ; to our knowledge, complexes 9-11 represent the fi rst examples for a system in which the redox properties of a ferrocenecarboxylate-based ligand is modifi ed by dinuclear aminethiophenolate complexes.
The magnetic properties of the pentanuclear Ni 4 Fe complex 13[BPh 4 ] 2 were examined in view of literature reports that conjugated dicarboxylate ligands can mediate long-range magnetic exchange interactions [45].Figure 11 displays the temperature dependence of the effective magnetic moment for 13[BPh 4 ] 2 .The effective magnetic moment increases from 6.88 μ B at 295K to a maximum value of 7.70 μ B at 25K.On lowering the temperature further the magnetic moment decreases to 7.08 μ B at 2 K.Although the effective magnetic moment at 25K is smaller than expected for the spin-only value of 9.84 μ B for S T = 4 resulting from the ferromagnetic coupling of four Ni II ions (S i = 1, g = 2.20), it is larger than the value of 6.22 μ B calculated for four noninteracting Ni II ions.This behaviour indicates the presence of weak ferromagnetic exchange interactions between the Ni II ions in the binuclear subunits but negligible -if anycoupling across the metallocene dicarboxylate bridge.Considering the long distance between the nickel(II) ions, this is not surprising.

Functionalized naphthalene diimide as a bifunctional linker
We and others have been working with naphthalene diimides as a suitable class of chemically robust redox-and photo-active units with which to explore molecular electronic applications [94,95].
The naphthalene diimides are a compact, electron-deficient class of aromatic compounds that allow further finetuning of their optical properties (absorbance and emission) via suitable core functionalization [95].The consideration that naphthalene diimides can act as ideal components for the creation of supramolecular functional materials has transpired as a result of their more desirable electronic and spectroscopic properties relative to pyromellitic diimides and better fabrication properties than the perylene diimide dyes, the latter being a result of their enhanced solubility properties.Naphthalene diimides (NDI) undergo single reversible one-electron reduction (chemically and electrochemically) at modest potentials (NDI: E 1 red ≈1.1 V vs.Fc/Fc + ) to form stable radical anions in high yield [96].They are seen as attractive redox-active units because of their electronic complementarity to ubiquinones [97] which make them excellent components for studying photoinduced electron transfer [98].Here we examine the interplay of a binucleating nickel(II) cavitand [LNi 2 (μ-Cl)][ClO 4 ](1) [1] with a naphthalene diimide 16 bearing two β-alanyl groups [99,100] (Scheme 6).
To our knowledge, complex 15 represents the first example of a supramolecular ensemble containing dinuclear amine-thiolate complexes and redox-active organic components within the same molecule.
Reaction of 1 with half an equivalent of 16 with NEt 3 in MeOH at r.t.leads to the immediate formation of a green solution.After the addition of a ten-fold excess of LiClO 4 a green microcrystalline solid, characterized as the 2:1 complex 15[ClO 4 ] 2 , is obtained in 72% yield.The perchlorate salt of 15 2+ is an air-stable solid that is readily soluble in polar aprotic solvents such as N,N-dimethylformamide, dichloromethane and acetonitrile, but virtually insoluble in methanol and water.The  The low energy bands at 360 and 380 nm which are typical for naphthalene diimides [96] further confirm the identity of complex 15 2+ .TheUV/Vis spectrum also reveals two weak d-d absorption bands at 644 and 1122 nm typical of octahedral Ni II in an N 3 S 2 O carboxylate environment.The observed values closely compare with those of 5 + (see inset in Fig. 12) again consistent with pseudo-octahedral N 3 S 2 O coordination environments around the metal atoms.All these findings strongly indicate that the tetranuclear complex 15 2+ retains its integrity in solution.
To determine whether 15 2+ exhibits electron transfer events due to the NDI unit and the [Ni  (15 4+ ).The redox-wave for the oxidation of the tetracation 15 4+ to the hexacation 15 6+ (formally a Ni II Ni III → Ni III Ni III process as seen for complex 5[ClO 4 ]) could not be detected.We assume that it is obscured by the redox-waves associated with the oxidation of the solvent.The observed potentials for the reduction of the naphthalene diimide ligand 16 are ca.100 mV more negative than those reported for other N-alkylated naphthalene diimides [95].Though there are many factors that could contribute to this significant effect, a simplistic thermodynamic view would argue that the influence of the aromatics within the cavitand structure on the NDI upon encapsulation is a strong contributor.The single peak value of 0.15 V measured for the Ni II → Ni III oxidation steps is almost identical to that observed for the model 5[ClO 4 ] (E = 0.11 V vs. Fc + /Fc) [29], indicating that the oxidation/reduction process on one [Ni 2 L] unit does not influence the processes that occur at the other site [75].In other words, the two dinuclear nickel(II) subunits behaveas two independent redox-groups.This observation is consistent with the large distance of ca.19 Å between the two subunits (see Fig. 14(a)) and the fact that the electrostatic (Coulombic) interactions decrease rapidly with increasing distance between two redox-sites.
The radical anion of the NDI within 15 + is characterised by a set of intense and characteristic visible and nearinfrared (NIR) absorption bands.Thus, the electronic spectrum of a solution of 15 + in DMF (generated by reduction of 15 2+ with an aqueous Na 2 S 2 O 4 solution) shows bands at 270 (50236), 283 (26840), 329 (28917), 373sh (1072), 400sh (8360), 474 (31586), 607 (9019), 682 (4738) and 756 nm (6618 M -1 cm -1 ).Similar values have been reported for other NDI radicals [95].The composition of the assembly as 15 2+ was confirmed by a single-crystal X-ray structure determination, as the tetraphenylborate salt 15[BPh 4 ] 2 (prepared by salt metathesis of 15[ClO 4 ] 2 with NaBPh 4 ).Crystals of 15[BPh 4 ] 2 •xCH 3 CN suitable for X-ray crystallography were grown by recrystallisation from MeCN.Fig. 14 displays a van der Waals representation of the centrosymmetric dication 15 formed within a triclinic crystal with space group P1.The dicarboxylate acts as a tetradentate bridging ligand joining two dinuclear [LNi II 2 ] 2+ fragments through its carboxylate functions.Each Ni atom is thus surrounded in a highly distorted octahedral fashion by two sulfur atoms and three nitrogen atoms from the supporting ligand L 2-, and one oxygen atom from the carboxylate groups of [16-2H] 2-.
The macrocycle assumes a rigid bowl-shaped conformation very similar to that found for [Ni 2 L(μ-OAc)][ClO 4 ] (5) [29].As a consequence, the [Ni 2 L] 2+ subunits in 15 and 5 are structurally very similar, and the Ni-N and Ni-S distances lie within very narrow ranges.The NDI ligand assumes a planar conformation and the Ni 2 O 2 planes are only slightly folded with respect to the NDI plane (folding angle = 15.1 o ).The NDI unit is not coplanar with the aromatic rings of the cavitand, the folding angles between the planes of the two aromatic rings of the cavitand and the plane through the NDI unit being 31.8o and 53.9 o , respectively.The Ni •••Ni distance of 3.481(1) Å is practically the same as that in 5.The distance between the center of the Ni•••Ni axes of the binuclear subunits are amounts to 19.010(1) Å.
Complex 15 is unique in the sense that its naphthalene diimide coligand is included within the two metallocavitands.To the best of our knowledge, this is the first structural report of such an inclusion complex.In contrast to 'free' NDI compounds, no π-π-stacking interactions involving the NDIs are present in 15, a fact attributable to the steric shielding of the [Ni 2 L] 2+ units.This feature is no doubt responsible for the enhanced solubility of the complex 15 over 16.Furthermore, limiting the ability for NDIs to stack has important implications for their use in molecular electronics by limiting aggregation and hence the excimer emission found in many systems

Conclusions
In summry, a series of novel tri-, tetra-and pentanuclear complexes composed of dinuclear LM 2 units (M=Co, Ni, Zn; L 2− = represents a macrocyclic hexaazadithiophenolate ligand) and ferrocenecarboxylate (CpFeC 5 H 4 CO 2 ˉ), 1,1'-ferrocenedicarboxylate(Fe(C 5 H 4 -CO 2 ) 2 2 ˉ), acetylenedicarboxylate, terephthalate, isophthalate, and naphthalene diimide dicarboxylate groups is reported.The complexes, have been synthesized and characterised by UV/Vis-, IRspectroscopy, and X-ray crystallography.Each dicarboxylate dianion acts as a quadridentate bridging ligand linking two bioctahedral LM 2 units via μ 1,3 -bridging carboxylate functions to generate discrete dications with a central LM 2 (O 2 C-R-CO 2 )M 2 L core.The structures differ mainly in the distance between the center of the Ni  (12)(13)(14) bridging ligands towards one or two bioctahedral LM 2 subunits, respectively.The structures are retained in solution as indicated by NMR spectroscopic studies on the diamagnetic ferrocenylcarboxylate [ClO 4 ].All complexes were found to exhibit a rich redox chemistry.Complexation of the ferrocenylcarboxylates by the LM 2 fragments results in large potential shifts of the ferrocenyl-centred redox process.The redox processes of the LM 2 units are also affected upon complex formation, showing that the electron transfer events of the ferrocenyl moiety and the binuclear subunit infl uence one another.In 14, however, the two dinuclear cobalt(II) subunits behave as two independent redox-groups owing to the large distance between them.Additionally, we found that the magnetic properties in the pentanuclear Ni 4 Fe complex 13 are based on the ferromagnetic exchange interactions between the Ni II ions in the binuclear subunits.The coupling across the metallocene dicarboxylate bridge is negligible.These results can now be used as a guide for further studies aimed at the synthesis of polynuclear complexes with novel electronic and magnetic properties.

Figure 2 .Figure 3 .
Figure 2. Left: Van der Waals representation of the [(LNi II 2 ) 2 (μ-terephthalato)] 2+ dication in crystals of 7[BPh 4 ] 2 •2EtOH•0.5MeCN•H 2 O. Middle: ORTEP representation of the core structure of 7 with the atom labeling scheme.Ellipsoids are represented at the 50% probability level.Right: Relative orientation of the Ni 2 carboxylato planes in 7. The [LNi 2 ] 2+ subunits in 6 and 7 are structurally very similar, and the Ni-N, Ni-O, and Ni-S distances lie within very narrow ranges.As in 6, the tBu groups of the two opposing Ni 2 clusters are forced to interlock to accommodate the terephthalato ligand.This causes tilting of the carboxylato planes that are rotated by 58.2° with respect to each other and by 19.1° and 39.1° with respect to the aromatic ring of the terephthalato coligand.Again, there are no intermolecular interactions between the tetranuclear complexes other than van der Waals contacts.The intramolecular Ni•••Ni distances between the two dinuclear subunits are within the range 10.833(1) -11.155(1)Å (mean 10.990(1) Å].This is a typical value for terephthalato-bridged nickel(II) complexes [40,41].Crystals of 8[BPh 4 ] 2 •4MeCN•EtOH are triclinic, space group P1.ORTEP views of the structure of the dication 8 and the central core are provided in Figure 3. p g
The 1 H NMR spectrum shows the characteristic signal patterns for the [LZn 2 ] 2+[78], and [CpFe(C 5 H 4 CO 2 )]‾[79], units indicating local C 2v symmetry for 11.Particularly indicative of a stable 1:1 complex is the upfi eld shift of the tert-butyl resonance of the [LZn 2 ] unit (0.25 ppm relative to 3).The resonances of the ferrocenecarboxylate are observed at δ 3.40 for the unsubstituted Cp ring, δ 3.90 for the two meta-H and δ 4.04 for the two ortho-H of the substituted Cp ring.These values are also signifi cantly shifted to higher fi eld when compared with the corresponding resonances of uncomplexed ferrocenmonocarboxylate[80, 81].The 13 C NMR spectrum is also in accord with the proposed formulation showing fi ve signals for the [CpFe(C 5 H 4 CO 2 )]‾ unit and only 13 signals for the [LZn 2 ] 2+ moiety.The local C 2v symmetry is suggestive of a dynamic averaging process in solution.A rapid rotation of the ferrocenyl group about the CpFeCp-CO 2 Zn 2 L bond seems most likely.This motion would result in the coalescence of the respective signals and the time averaged C 2v symmetry of the complex.The crystal structure determinations of 9 and 10 support this assumption.

14 [ 77 Figure 5 .
Figure 5. Structure of the cation 9 in crystals of 9[BPh 4 ]•3MeCN.Thermal ellipsoids are drawn at the 30% probability level.Hydrogen atoms are omitted for reasons of clarity.Only one orientation of a rotationally disordered tBu group is shown.

Figure 6 .
Figure 6.Structure of the cation 10 in crystals of 10[BPh 4 ]•MeCN.Thermal ellipsoids are drawn at the 30% probability level.Hydrogen atoms are omitted for reasons of clarity.Only one orientation of a rotationally disordered tBu group is shown.
, the ferrocenyldicarboxylate dianion links two [LCo II 2 ] 2+ units via two μ 1,3 -bridging carboxylate functions.The [LCo 2 ] 2+ subunits in 12 and 4 are structurally very similar, and the Co-N, Co-O, and Co-S distances lie within very narrow ranges.The carboxylato groups on the Cp rings assume an anti-eclipsed conformation as manifested by a torsional angle τ (CO 2 -centroid-centroid-CO 2 ) of 148.4 o [148.3 o ].The distance d between the centre of the Co•••Co axes of the binuclear subunits amounts to 10.751 Å [10.749Å], which is slightly smaller than the corresponding distance in [Mo 2 (DAniF) 3 ] 2 [ferrocendicarboxylate] [64].It should be noted that the Co 2 carboxylato planes are considerably tilted against each other (32.3 o , [33.1 o ]) and also with respect to their corresponding Cp rings (22.4 o , 10.1 o ; [22.4 o , 10.0 o ]).This distortion from coplanarity relates to steric interactions between the tBu groups of the two opposing [LCo II 2 ] 2+ subunits.The tert-butyl groups must interlock to accommodate the dicarboxylate ion.In ferrocenedicarboxylato complexes of sterically less encumbered supporting ligands the carboxylato planes are both coplanar with their parent Cp rings [87, 88].The crystal structure of 14[ClO 4 ] 4 •4H 2 O consists of [(LCo II Co III ) 2 (μ-O 2 CC 5 H 4 ) 2 Fe] 4+ cations (Figure 8), ClO 4 ‾ anions and water solvate molecules.There are two crystallographically independent but chemically almost identical molecules (labelled A and B) in the asymmetric unit; both have crystallographically imposed C 2 symmetry with the iron atoms residing on crystallographic two-fold axes.The overall structure of complex 14 is very similar to that of its parent 12, featuring two binuclear LCo 2 subunits linked by a tetradentate ferrocenedicarboxylate ion.Again, the carboxylato Chemistry Journal of Moldova.General, Industrial and Ecological Chemistry.2013, 8 (1), 58-77 groups are anti-eclipsed (τ = 148.6 o [136.9 o (molecule B)] and considerably tilted against each other (48.2 o , [25.2 o ]) and by 24.1 o [12.6 o ] with respect to their corresponding Cp rings.The distance d between the centre of the Co•••Co axes is 10.770 Å in molecule A and 10.322 Å in molecule B.

Figure 11 .
Figure 11.Temperature dependence of μ eff (per tetranuclear complex) for 13[BPh 4 ] 2 .The full line represents the best theoretical fi t.The dashed line represents the best fi t to the dimer model.
2 L] 2+ groups, cyclic voltammetric studies have been carried out on 15[ClO 4 ] 2 in DMF solution using 0.10 M [ n Bu 4 N][PF 6 ] as the supporting electrolyte (Fig. 13).The CV of the Ni 4 complex 15[ClO 4 ] 2 shows three redox waves at -1.62, -1.04 and 0.15 V, respectively, vs. ferrocenium /ferrocene (Fc + /Fc).The processes at -1.04 and -1.62 V correspond to the reduction of the dication 15 2+ to 15 + (bearing the radical anion 16 -• ) and the reduction of 15 + to neutral 15 (bearing the doubly reduced NDI ligand), respectively.Upon reduction of 15 2+ by either electrochemical or chemical means (Na 2 S 2 O 4 /H 2 O) the colour of the complex changes to deep mauve which (in the absence of air) persists in solution over 3 h indicative of radical anion formation.The redox wave located at 0.15 V on the other hand is tentatively assigned to a two-electron metal-centered Ni II Ni II → Ni II Ni III oxidation yielding the mixed-valent tetrametallic tetracation [(Ni III Ni II L) 2 (16)] 4+

Figure 14 .
Figure 14.(a) van derWaals representation of the molecular structure of the dication 15 2+ in crystals of 15[BPh 4 ] 2 .(b) Asymmetric unit of 15 2+ with thermal ellipsoids drawn at the 30% probability level, hydrogen atoms and MeCN solvent are omitted for clarity.(c) Packing of individual molecules in the crystal lattice of 15[BPh 4 ] 2 (BPh 4 ¯ anions and solvent acetonitrile molecules are omitted for clarity).

Table 1 Electrochemical data, E[V] vs SCE, for the compounds examined in this study. [b] Compound Solvent Fe III /Fe II E 1/2 [V] (∆Ep [mV]) b M III M II /M II 2 M III 2 /M III M II RS‾/RS
11[ClO 4 ] are summarized in Scheme 5.