A new family of high nuclearity CoII / DyIII coordination clusters possessing robust and unseen topologies †

Mixing Co(NO3)2·6H2O/Dy(NO3)3·6H2O/(E)-4-(2-hydroxy-3-methoxybenzylideneamino)-2,3-dimethyl-1phenyl-1,2-dihydropyrazol-5-one (HL)/pivalic acid/Et3N in various solvents results in the synthesis of seven compounds formulated as [Co 2Dy III 2 (μ3-MeO)2(L)2(piv)4(NO3)2] (3), [Co Dy 3 (μ3-MeO)2(μ2MeO)2(L)2(piv)2(NO3)3]·2(CH3OH) (4·2CH3OH), 2[Co II 4Dy III 4 (μ2-O)2(μ3-OH)4(L)4(piv)8][Co II 2Dy III 5 (μ3-OH)6(L)2(piv)8(NO3)4] (5), [Co II 4Dy III 4 (μ2-O)2(μ3-OH)4(L)4(piv)8]·2(CH3CN) (6·2CH3CN), [Co II 2Dy III 5 (μ3-OH)6(L)2(piv)8(NO3)4]·4(CH3CN) (7·4CH3CN), [Co II 2Dy III 2 (μ3-OH)2(L)2(piv)2(NO3)2(EtOH)2(H2O)2](NO3)2·(EtOH) (8·EtOH) and [Co 4Dy III 4 (μ2-O)2(μ3-OH)4(L)4(piv)8] (9) with robust and unseen topologies. These show that the temperature and reaction time influence the formation of the final product. Preliminary magnetic studies, performed for 6 and 7 in the temperature range 2–300 K, are indicative of Single Molecule Magnet (SMM) behaviour. Moreover, analysis of the catalytic properties of compound 3 as an efficient catalyst for the synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary amines has been carried out.


Introduction
7][8][9] The simple preparative procedure and the wide range of 3d, 4f elements and organic ligands that can be used have led to numerous compounds with unprecedented structures. 10The high coordination numbers that lanthanides favour make prediction and description of the final product difficult.Recognizing the importance of topology in the development of coordination polymer chemistry, 11 and aiming to create order in the fast-expanding group of polynuclear coordination clusters (CCs), we have developed a methodology which simplifies the description of the complicated structures of such species. 12,13This methodology classifies 14,15 and compares polynuclear CCs of defined nuclearity and topology 14 and allows a graphical search for structural motifs. 16 recently employed (E)-4-(2-hydroxy-3-methoxybenzylideneamino)-2,3-dimethyl-1-phenyl-1,2-dihydropyrazol-5-one (HL, (Scheme 1, left)) in Co/Ln chemistry, in the absence of a coligand to give two isoskeletal Co II 3 Dy III 4 CCs formulated as [Co II 3 - Dy III 4 -(µ 3 -OH) 6 L 6 (CF 3 SO 3 )](ClO 4 ) 5 (1) and [Co II 3 Dy III 4 (µ 3 -OH) 6 L 6 -(CF 3 SO 3 )](ClO 4 ) 3 (CF 3 SO 3 ) 2 (2) possessing a disk-like or 3,6M7-1 topology, previously unseen in Co/Ln chemistry and exhibiting interesting magnetic properties. 17The two different coordination pockets, the limited degree of flexibility of the ligand, the unusual Co/Dy topology and the higher nuclearity afforded in comparison with compounds containing similar ligands, 18 lead us to explore the coordination chemistry of HL in more detail and to undertake a systematic investigation.

Experimental
Materials and methods Materials.Chemicals (reagent grade) were purchased from Sigma Aldrich and Alfa Aesar.All experiments were performed under aerobic conditions using materials and solvents as received.
Instrumentation.NMR spectra were recorded on a Varian VNMRS solution-state spectrometer at 500 MHz at 30 °C using residual isotopic solvent (DMSO, δ H = 2.50 ppm) as an internal reference.Chemical shifts are quoted in ppm.Coupling constants ( J) are recorded in Hz.IR spectra of the samples were recorded over the range of 4000-650 cm −1 on a Perkin Elmer Spectrum One FT-IR spectrometer fitted with a UATR polarization accessory.EI-MS was performed on a VG Autospec Fissions instrument (EI at 70 eV).

Synthetic procedures
Ligand synthesis.The synthesis of HL has been carried out according to the reported synthetic procedure. 17ynthesis of [Co II 2 Dy III 2 (µ 3 -MeO) 2 (L) 2 ( piv) 4 (NO 3 ) 2 ] (3).0.075 g (0.22 mmol) of L and 0.036 g (0.35 mmol) of pivalic acid were added to 20 ml of MeOH and stirred.To this 118 μl (0.84 mmol) of 99% NEt 3 were added and the resulting mixture was brought to 40 °C and stirred for 10 minutes.To this 0.068 g (0. Synthesis of [Co II Dy III 3 (µ 3 -MeO) 2 (µ 2 -MeO) 2 (L) 2 ( piv) 2 (NO 3 ) 3 ]• 2(CH 3 OH) (4).0.075 g (0.22 mmol) of L and 0.036 g (0.35 mmol) of pivalic acid were added to 20 ml of MeOH and stirred.To this 118 μl (0.84 mmol) of 99% NEt 3 were added and the resulting mixture was brought to reflux and stirred for 10 minutes.To this 0.068 g (0. . 0.075 g (0.22 mmol) of L and 0.036 g (0.35 mmol) of pivalic acid were added to 20 ml of MeCN and stirred.To this 118 μl (0.84 mmol) of 99% NEt 3 were added and the resulting mixture was brought to reflux and stirred for 10 minutes.To this 0.068 g (0.23 mmol) of Co II (NO 3 ) 2 •6H 2 O and 0.104 g (0.23 mmol) of Dy III (NO 3 ) 3 •5H 2 O were added and the resulting mixture was refluxed for a further hour.This was then filtered and left undisturbed for slow evaporation; red hexagonal plate like crystals of 6 formed within 48 hours.Yield: 18.2 mg (10.4% based on Co).Selected IR peaks (cm −1 ): 2958.46   (7).0.075 g (0.22 mmol) of L and 0.036 g (0.35 mmol) of pivalic acid were added to 20 ml of MeCN and stirred.To this 118 μl (0.84 mmol) of 99% NEt 3 were added and the resulting mixture was brought to reflux and stirred for 10 minutes.To this 0.068 g (0.23 mmol) of Co II (NO 3 ) 2 •6H 2 O and 0.104 g (0.23 mmol) of Dy III (NO 3 ) 3 •5H 2 O were added and the resulting mixture was refluxed for a further 24 hours.This was then filtered and left undisturbed for slow evaporation; orange rectangular plate like crystals of 7 formed within 72 hours.Yield: 16 mg (13.0%based on Dy).Selected IR peaks (cm  (8).0.075 g (0.22 mmol) of L and 0.036 g (0.35 mmol) of pivalic acid were added to 20 ml of EtOH and stirred.To this 118 μl (0.84 mmol) of 99% NEt 3 were added and the resulting mixture was brought to reflux and stirred for 10 minutes.To this 0.068 g (0.23 mmol) of Co II (NO 3 ) 2 Conversion of 8 to 6. 10 mg (0.00623 mmol) of 8 was added along with 1.27 mg (0.01246 mmol) of pivalic acid to 5 ml MeCN.To this 0.86 μl (0.00623 mmol) of 99% NEt 3 were added and the resulting mixture was stirred and refluxed for 24 hours.Crystals of 6 were formed within 72 hours.Conversion of 8 to 9. 10 mg (0.00623 mmol) of 8 was added along with 1.27 mg (0.01246 mmol) of pivalic acid to 5 ml EtOH.To this 0.86 μl (0.00623 mmol) of 99% NEt 3 were added and the resulting mixture was stirred and refluxed for 24 hours.Crystals of 9 were formed within 72 hours.
Magnetic studies.Magnetic susceptibility measurements were carried out on polycrystalline samples with a MPMS5 Quantum Design susceptometer working in the range 30-300 K under an external magnetic field of 0.3 T and under a field of 0.03 T in the 30-2 K range to avoid saturation effects.Diamagnetic corrections were estimated from Pascal Tables.
Crystallography.Data for 4 and 8 were collected (ω-scans) at the University of Sussex using an Agilent Xcalibur Eos Gemini Ultra diffractometer with a CCD plate detector under a flow of nitrogen gas at 173(2) K using Mo Kα radiation (λ = 0.71073 Å).CRYSALIS CCD and RED software were used respectively for data collection and processing.Reflection intensities were corrected for absorption by the multi-scan method.Data for 3, 5, 6, 7, 8′ and 9 were collected at the National Crystallography Service, University of Southampton 26 using a Rigaku Saturn 724+ area detector mounted at the window of an FR-E+ rotating anode generator with a Mo anode (λ = 0.71075 Å) under a flow of nitrogen gas at 100(2) K.All structures were determined using Olex2, 27 solved using either Superflip 28 or SHELXT 29,30 and refined with SHELXL-2014. 31All non-H atoms were refined with anisotropic thermal parameters, and H-atoms were introduced at calculated positions and allowed to ride on their carrier atoms.Geometric/crystallographic calculations were performed using PLATON, 32 Olex2, 27 and WINGX 29 packages; graphics were prepared with Crystal Maker. 33rystallographic details for 3-9 are given in Table S1.†

Results and discussion
Some general observations for all compounds are: (a) except 4, each L − is chelated to a Co II centre, forming a cationic metalloligand, (CoL) + , which in turn is linked to other metal centres, (b) L − is coordinated to three metal centres exhibiting two different coordination modes (modes I and II, Scheme 2, above), (c) two coordination modes can be found for the coligand (Scheme 2, below), (d) Co II centres are six coordinated in an essentially regular octahedral coordination and (e) the coordination spheres of the Dy centres are completed by the carboxylate and the nitrate groups.
By changing the reaction conditions that afforded 1, 17 introducing pivalic acid as a co-ligand, and heating at 40 °C for one hour (Table 1, entry 1), we obtained orange diamond-shaped crystals of compound 3 (Fig. 1a).The structure, confirmed by X-ray studies, 26 possesses the well-known defect dicubane 34 or, according to our nomenclature, 2,3M4-1 13 topology.The coordination number of the two Dy III ions is 8. Using Shape software, 35 the geometry of Dy(1) can be best described as biaugmented trigonal prism or square antiprism [S(P) values 1.767 and 1.968, respectively] and of Dy(2) as biaugmented trigonal prism [S(P) = 2.372].
The orange needles obtained under reflux (Table 1, entry 2) were found to be 4•2(CH 3 OH) (Fig. 1b), also possessing the defect dicubane or 2,3M4-1 topology.In this compound, two L − are chelated to a Co II centre, forming a neutral metalloligand, (CoL 2 ), which in turn is linked to the Dy III centres.The coordination number of all Dy III ions is 8. Using Shape software, 35 the geometry of Dy(1) can be best described as intermediate between heptagonal pyramid and Johnson elongated triangular bipyramid, and the geometry of Dy(2) can be best described as an intermediate of Johnson gyrobifastigium, 36 biaugmented trigonal prism and elongated trigonal bipyramid.The lattice methanol is hydrogen bonded to the chelated nitrate group of Dy(2).Reaction for a longer time (Table 1, entry 3) again gave 4, confirmed by a unit cell check.To the best of our knowledge, such a defect dicubane Co II Dy III 3 topology has not previously been reported.In both 3 and 4, MeO groups, arising from solvent deprotonation, bridge the metal centres in a µ 2 -or µ 3 -fashion and, the structure is unchanged, even after prolonged heating under reflux.
As the complexes required bridging MeO groups to give a defect dicubane geometry it would be reasonable to suggest that a non-coordinating solvent may result in different topologies.Indeed, repetition of the reaction that afforded 3 in CH 3 CN instead of CH 3 OH (Table 1, entry 4), results in orange hexagonal crystals of 5 (Fig. 1c), the lattice of which contains two octanuclear and one heptanuclear Co II /Dy III unit.The octanuclear one can be considered as two Co II 2 Dy III 2 cubanes joined by two oxo bridges, and bridged by four pivalates, possessing a 3,4M8-3 topology (Table 1, entry 4) and the heptanuclear fragment possesses a disk-like or 3,6M7-1 topology.According to our survey, both topologies are unprecedented in Co/Ln chemistry, and mixed nuclearity CCs are very rare in coordination chemistry as a whole. 37The unusual 3,4M8-3 topology can be found in compounds containing solely Fe, 38,39 Zn 40 and Dy 41 but not in mixed metal species.Additionally, the 3,6M7-1 topology has been seen in mixed valence Co II/III42-44 and Dy III45 compounds, in a series of Mn II 3 Ln III 4 , 46 51,52 Triply bridging hydroxyl groups further support the formation of both species.In the  1, entry 5), only compound 6•2CH 3 CN was isolated and characterized (Fig. 1d).Compound 6 is identical to the octanuclear species found in 5.The coordination number of the four Dy III ions is 8. Using Shape software, 35 the geometry of both Dy III ions can be best described as triangular dodecahedron, S(P) = 0.790.A further increase of the reaction time to 24 hours (Table 1, entry 6) results in the isolation of only compound 7•4CH 3 CN (Fig. 1e) which is identical to the heptanuclear species found in 5.This indicates a rearrangement to a species in which the Co/Dy ratio is different.The coordination numbers of the three peripheral and the central Dy III ions are 8 and 7, respectively.The geometry of the central Dy III ion can be best described as capped octahedron and of the four wheel Dy III as bicapped trigonal prism.Thus, the solvent has a major effect on the adopted topology in this family of CCs.The use of CH 3 CN does not provide a link between the metal centres; instead it promotes hydrolysis of the metal salts to give CCs of higher nuclearity.The differences in temperature and reaction time in the synthesis of 5-7 influence the final product.A unit cell check of twenty random samples selected from three different vials gave identical unit cells, indicating that formation of 5-7 was reproducible.
The next step was to incorporate a protic solvent that has similar coordination ability to MeOH but is more bulky.The additional bulk should prevent the formation of bridges to give the defect dicubane geometry.Indeed, a reaction in EtOH at 40 °C for 1 hour (Table 1, entry 7) resulted in the formation of a dicationic tetranuclear compound 8•EtOH possessing a cubane (Fig. 1f ) or 3M4-1 topology (Table 1, entry 7).Two triply bridging hydroxyl groups further enhance the formation of the cubane topology, while ethanol and water molecules fill the vacant positions on the two Dy III centres.The coordination number of the two Dy III ions is 9.The geometry of both Dy III ions can be best described as Spherical capped square antiprism [S(P) = 1.144].This cubane topology has been reported previously only once in Co/Ln chemistry. 53Most of the known tetranuclear Co 2 Dy 2 compounds possess a defect dicubane topology.
Thus, the employment of EtOH as a solvent prevents the formation of EtO bridges and promotes partial hydrolysis of the metal centres to give a cubane unit.From the decorated topologies 12 (Table 1, entries 7 or 8 and 5) compound 8 can be considered as half the octanuclear species found in 6. 6 could be formed by linking two cubane units by double deprotonation of a coordinated H 2 O molecule to form a µ 2 -O bridge.At the same time, replacement of two coordinated NO 3 , two EtOH and the remaining coordinated H 2 O molecules in each cubane by pivalate groups further stabilizes the octanuclear species.The formation of 8 was achieved in one hour at 40 °C, thus the next step is to confirm that 8 is indeed an intermediate in the formation of 6.This could be done in two ways: (a) by showing that an increase in temperature or time affords an octanuclear species isoskeletal to 6 and (b) by converting 8 to 6 in an independent reaction.Reaction under reflux conditions for an hour (Table 1, entry 8) afforded compound 8•2(EtOH), which crystallized in a different space group.However, reaction for 24 hours under reflux (Table 1, entry 9) afforded compound 9, isoskeletal to 6. Furthermore, heating 8 for 24 hours under reflux in EtOH or CH 3 CN, in the presence of 2 equivalents of pivalic acid and 1 equivalent of Et 3 N, resulted in the formation of 9 or 6, respectively (Scheme 3), as confirmed by unit cell check and IR.
To confirm the identity of these compounds in solution, we made use of electrospray ionization mass spectrometry Since a tetranuclear Co II 2 Dy III 2 compound 9 is an efficient catalyst for the synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary and secondary amines, we used compound 3 as a catalyst in this domino reaction (Scheme 4 and Table 2).Loadings of 1% and 2.5% for 2 h resulted in 43% and 73% yields, respectively.A loading of 10% for 8 h showed the highest yield of 95%.No significant improvement in yield was observed for any % loading over 8 hours.A fourfold decrease in catalyst loading for 8 h (2.5%) still shows good yields (85%), however these are lower than the previously mentioned Co II 2 Dy III 2 compound, 9 suggesting that catalytic efficiency is highly dependent on the coordination environment of the Dy III centres.Efforts to recover the catalyst were not successful, while theoretical studies on this aspect are in progress.
The room temperature χ M T values for 6 and 7 (62.5 and 75.4 cm 3 K mol −1 , respectively) are in agreement with the expected values of 64.18 and 74.60 cm 3 K mol −1 for four noninteracting Dy III ( 6 H 15/2 free ion; S = 5/2; L = 5; g J = 4/3) centres, and four Co II ions or five non-interacting Dy III and two Co II respectively (Fig. 2).Upon cooling, the χ M T products decrease monotonically for 6 reaching 40.7 cm 3 K mol −1 at 2 K and down to a quasi-constant value around 63 cm 3 K mol −1 for 7.This decrease is mainly due to the progressive depopulation of the Dy III excited Stark sublevels.The relativity high χ M T value and the absence of decay at low temperature for 7, as well its fast magnetization (Fig. S10 †), may also suggest weak intramolecular ferromagnetic coupling.In the light of the susceptibility responses, alternating-current (ac) preliminary magnetic susceptibility measurements were performed on polycrystalline samples of 6 and 7 (Fig. S11 †).In a zero applied dc field and a 4 G ac field oscillating at 1000 and 10 Hz frequencydependent out-of-phase (χ″ M ) weak tails were observed, but no peaks were seen even under a dc field of 0.1 T, suggesting a weak single-molecule magnet response clearly below 2K.
The CCs presented here show how major differences in the core motif are caused by subtle changes in reaction conditions.The employment of HL in Co/Dy chemistry affords, compounds (a) with Co in oxidation state II and (b) with hitherto unobserved topologies that are preserved in alcoholic solvents.The most important feature of HL is that despite being monoanionic and showing a coordination environment similar to that in other ligands, 18 it gives CCs with higher nuclearity.Two different coordination modes are seen for HL in compounds 3-9 (Scheme 2), however despite the increase in reaction temperature no increase in the number of bridging metal centres is observed.In protic solvents, the ligand coordinates

Conclusions
The formation of the double cubane 9 either from the single cubane 8 or by increased reaction time and temperature (Table 1, entry 9) represents an interesting example in coordination chemistry.The structural relationship of compounds 6, 9 and 8 can immediately be visualized (Scheme 3) from topological analysis.Since the coordination chemistry of HL is still insufficiently delineated, further studies are required that will reveal its coordination behaviour and lead to a library of CCs.
We are extending this study to: (a) more complicated systems to explore synthesis of CCs with higher nuclearity and (b) compounds of other 3d and 4f elements to investigate their magnetic and photoluminescent properties.

Scheme 2 (
Scheme 2 (Above) The two coordination modes of the ligand.Mode I is seen in compounds 3, 4, 5 and 7, mode II is seen in 5, 6, 8, 8' and 9. (Below) The two coordination modes seen in 3-9 for the pivalate anion.
This was then filtered and left undisturbed for slow evaporation.Crystals of 5 were formed within 72 hours.Yield: 28 mg (17% based on Dy).

Table 1
A summary of the reaction conditions for the formation of 3-9 reaction in CH 3 CN under reflux conditions for an hour (Table

Table 2
Comparison of catalytic activity for compound 3 , but this can be attributed to the existence of further MeO bridges.The final products are influenced by the temperature and the reaction time.When CH 3 CN is used as a solvent, a mixed octanuclear and heptanuclear CC product is obtained (Table 1, entry 4) and when the reaction takes place under reflux (Table 1, entries 5 and 6), distinct octanuclear (Table 1, entry 5) and heptanuclear (Table 1, entry 6) CCs are obtained.Even with changes of solvents viz. to CH 3 CN (Table 1, entry 5) and EtOH (Table1, entry 9) and reaction times, isoskeletal products are obtained.For this specific reaction system, an increase in the reaction temperature enhances deprotonation of water molecules to form OH − and/or O 2− species leading to CC clusters of higher nuclearity in CH 3 CN and EtOH.