Heterobimetallic Coordination Polymers Research Articles

Synthesis, structure and photoluminescence properties of heterometallic-based coordination polymers of trimesic acid.

Reacting trimesic acid (H3TMA, C9H6O6) with CaCl2 and MCl2 at 110 °C under hydrothermal conditions gave the isostructural heterobimetallic coordination polymers (CPs) catena-poly[[tetraaquazinc(II)]-μ-5-carboxybenzene-1,3-dicarboxylato-[tetraaquacalcium(II)]-μ-5-carboxybenzene-1,3-dicarboxylato], [CaZn(HTMA)2(H2O)8]n, 1, and catena-poly[[tetraaquacobalt(II)]-μ-5-carboxybenzene-1,3-dicarboxylato-[tetraaquacalcium(II)]-μ-5-carboxybenzene-1,3-dicarboxylato], [CaCo(HTMA)2(H2O)8]n, 2. Compounds 1 and 2 crystallize in the monoclinic space group C2/c. The solid-state structures consist of eight-coordinate CaII ions and six-coordinate MII ions. These ions are connected by a doubly deprotonated HTMA2- ligand to create a one-dimensional (1D) zigzag chain. Poly[[decaaquabis(μ3-benzene-1,3,5-tricarboxylato)calcium(II)dizinc(II)] dihydrate], {[CaZn2(TMA)2(H2O)10]·2H2O}n, 3, was found incidentally as a minor by-product during the synthesis of 1 at a temperature of 140 °C. It forms crystals in the orthorhombic space group Ccce. The structure of 3 consists of a two-dimensional (2D) layer composed of [Zn(TMA)] chains that are interconnected by CaII ions. The presence of aromatic carboxylic acid ligands and water molecules, which can form numerous hydrogen bonds and π-π interactions, increases the stability of the three-dimensional (3D) supramolecular architecture of these CPs. Compounds 1 and 2 exhibit thermal stability up to 420 °C, as indicated by the thermogravimetric analysis (TGA) curves. The powder X-ray diffraction (PXRD) data reveal the formation of unidentified phases in methanol and dimethyl sulfoxide, while 1 exhibits chemical stability in a wide range of solvents. The luminescence properties of 1 dispersed in various low molecular weight organic solvents was also examined. The results demonstrate excellent selectivity, sensitivity and recyclability for detecting acetone molecules in aqueous media. Additionally, a possible sensing mechanism is also outlined.

One-Dimensional Heterobimetallic Au/Ag Coordination Polymer Showing a Selective, Reversible, and Visible Vapor-Chromic Photoluminescent Response toward Methanol.

A heterobimetallic coordination polymer [Au4(dppmt)4(AgCl)2]n (1) incorporating an in situ generated P-S ligand (dppmtH) was synthesized from the solvothermal reaction of Au(tht)Cl, AgCl, and dpppyatc in CH3CN/CH2Cl2 (dppmtH = (diphenylphosphino)methanethiol, tht = tetrahydrothiophene, dpppyatc = N,N-bis((diphenylphosphaneyl)methyl)-N-(pyridin-2-yl)-amino-thiocarbamide). The structure of 1 contains a one-dimensional helical Au-Au chain in which the unique [Au4Ag2S2] cluster units are connected by [Au2(dppmt)2] dimers. Upon excitation at 343 nm, 1 exhibited cyan (495 nm) phosphorescent emission at quantum yield (QY) = 22.3% and τ = 0.78 μs (λex = 375 nm). Coordination polymer 1 exhibited a rapid, selective, reversible, and visible vapor-chromic response on exposure to methanol (MeOH) vapor with its emission shifting to a more intense green (530 nm, λex = 388 nm) with QY = 46.8% and τ = 1.24 μs (λex = 375 nm). A polymethylmethacrylate film containing 1 served as a reversible chemical sensor for the sensitive detection of MeOH in air.

Coinage Metal Bis(amidinate) Complexes as Building Blocks for Self-Assembled One-Dimensional Coordination Polymers.

The pyridyl functionalized amidinate [{PyC≡CC(NDipp)2 }Li(thf)2 ]n was used to synthesize a series of bis-amidinate complexes [{PyC≡CC(NDipp)2 }2 M2 ] (M=Cu, Ag, Au) with fully supported metallophilic interactions. These metalloligands were then used as building blocks for the synthesis of one-dimensional heterobimetallic coordination polymers using Zn(hfac)2 (hfac=hexaflouroacetylacetonate) for self-assembly. Interestingly, the three coordination polymers [{PyC≡CC(NDipp)2 }2 M2 ][Zn(hfac)2 ] (M=Cu, Ag, Au), exhibit a zig zag shape in the solid state. To achieve linear coordination geometry other connectors such as M'(acac) (M'=Ni, Co) (acac=acetylacetonate) were investigated. The thus obtained compounds [{PyC≡CC(NDipp)2 }2 Cu2 ][M'(acac)2 ] (M'=Ni, Co) are indeed linear heterobimetallic coordination polymers featuring a metalloligand backbone with fully supported metallophilic interactions.

A Bispidine Based CuII/ZnII Heterobimetallic Coordination Polymer

AbstractThe metalloligand approach was used to obtain a novel CuII/ZnII heterobimetallic coordination polymer (CP) 1, based on the carefully designed bispidine ligand L4. CP 1, characterized by single crystal (SC‐) and powder X‐ray diffraction methods (P‐XRD), is constituted by repeating large 32‐membered macrocycles forming ribbon‐like linear arrays and it features a CuII‐coordination site occupied by a markedly labile MeCN. We also describe the synthesis and characterization of intermediate metalloligands (with CuII, FeIII, MnII, and PdII, the latter three obtained as SCs and characterized accordingly) and provide a view of potential intermediate species along the route from metalloligands to heterometallic CPs.

Phosphorus or nitrogen - the first phosphatriptycene in coordination polymer chemistry.

Phosphasilatriptycene, a phenylene spacer and a pyridyl moiety represent the building blocks of TRIP-Py, the first heteroditopic ligand featuring a phoshatriptycene scaffold. The P and N donor sites located at opposite ends of the prolate TRIP-Py molecule selectively coordinate metal cations matching their Pearson character. The harder pyridyl donor binds to ZnII, the softer phosphorus donor to PtII, HgII and AuI. The remarkably short Au-P bond in the latter underlines the good π acceptor character of the phoshatriptycene moiety. When both the chloride salts of hard ZnII and soft AuI cations are available for coordination, TRIP-Py acts as selective ditopic linker in the discrete trinuclear mixed-metal complex [ZnCl2(TRIP-PyAuCl)2]. For CdII, a cation with intermediate Pearson character, selectivity withers, and a monometallic coordination polymer is obtained. Its significantly elongated Cd-P coordinative bonds underline, however, the preference of CdII for the harder N donor. When ZnII and HgII halides are combined, their preference for the matching donor sites in TRIP-Py and for tetrahedral coordination afford 1D and 2D heterobimetallic polymers with and without solvent-accessible voids. TRIP-Py enables the use of two important analytical tools: its rigidity facilitates crystallization and allowed to investigate 14 crystalline solids, and its P donor provides a powerful NMR probe for coordination.

Synthesis, characterization and antimicrobial studies of 1D hetero-bimetallic coordination polymers of pyridine-2,6-dicarboxylic acid with iron and alkaline earth metals

Three hetero-bimetallic coordination polymers {[Fe3Ca(PDA)5(H2O)6Cl]n.2nH2O} (1), {[Fe3Sr(PDA)5(H2O)6Cl]n.2nH2O} (2) and {[Fe3Ba(PDA)5(H2O)6Cl]n.2nH2O} (3) (PDA = pyridine-2,6-dicarboxylate anion) have been synthesized and characterized structurally by FT-IR and single crystal X-ray diffraction study, thermally by TG-DTG analysis and magnetically by VSM analysis. All the complexes are isomorphs with orthorhombic crystal system and exist as one dimensional coordination polymers. Antimicrobial activity of all compounds was investigated against micro-organisms, Escherichia coli (ATCC 25922), Klebsiella pneumonia (ATCC 13883), Pseudomonas aeroginosa (ATCC 27853), Staphylococcus aureus (ATCC 25923), Streptococcus mutans (MTCC 890), Aspergillus niger (ATCC 16404) and Candida albicans (ATCC 10231).

N-Donor-Functionalized Acetylacetones for Heterobimetallic Coordination Polymers, the Next Episode: Trimethylpyrazoles

The ditopic molecule 3-(1,3,5-trimethyl-4-1H-pyrazolyl)acetylacetone (HacacMePz) combines an acetylacetone group suitable for deprotonation and O,O′ coordination to a Pearson hard cation with a softer N-donor site. Both binding modes were employed individually: the pyrazolyl moiety was coordinated to ZnII, HgII, and AgI, and with trivalent iron the tris-chelating O,O′ complex [Fe(acacMePz)3] was isolated. The CuII derivative shows shorter O,O′ chelation and N coordination in the more distant Jahn–Teller sites and exists in two alternative crystal forms: namely, as a tetranuclear discrete complex and as a chain polymer. The different Pearson hardnesses of the coordination sites of acacMePz– allow for the design of well-ordered mixed-metal solids. Selective complexation to a hard and soft cations was achieved in coordination polymers combining hard FeIII and softer HgII or AgI. Even slight differences in Pearson hardness based on different oxidation states of the same cation imply sufficient selectivity, as shown by the successful synthesis of a mixed-valence CuII/CuI chain polymer. A synopsis of all structurally characterized compounds confirms that HacacMePz represents a bridging ligand with restricted conformational freedom. No full rotation about the single bond between the pyrazolyl and acetylacetone fragments occurs, and dihedral angles between these moieties are limited to values of 90 ± 17°.

Syntheses, structures and thermal stability of three heterobimetallic CuIILnIII (Ln = Tb, Tm and Y) coordination polymers bridged by formate

Using formate, three heterobimetallic CuIILnIII coordination polymers (CPs), [(Cu(Cl)(valen)Ln(NO3)(CH3OH)(μ-HCOO)]n [H2valen = 1,2-ethanediylbis(2-iminomethylene-6-methoxy-phenol); Ln = Tb(1), Tm(2), Y(3)], were synthesized and characterized by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction analyses. In these complexes, Cu ions are five-coordinate with an elongated square pyramidal (C 4v) geometry, while the Ln (Tb, Tm and Y) ions are nine-coordinate with a muffin (C s) geometry. In 1-3, the formate bridging ligands adopt a syn-anti coordination mode and cross-link the [(Cu(Cl)(valen)Ln(NO3)(CH3OH)]+ units into infinite zigzag chains, which are further connected by C-H···O and the C-H···Cl interactions to form 3 D supramolecular structures. In addition, the thermal stabilities of 1-3 were studied. This article offers a promising method for the design of 3d-4f molecular architectures with formate.

Insights into nature of a magnetization plateau of 3d-4f coordination polymer [Dy2Cu2]n from a spin-1/2 Ising-Heisenberg orthogonal-dimer chain

The ground state and magnetization process of an exactly solved spin-1/2 Ising-Heisenberg orthogonal-dimer chain with two different gyromagnetic factors of the Ising and Heisenberg spins are investigated in detail. It is shown that the investigated quantum spin chain exhibits up to seven possible ground states depending on a mutual interplay of the magnetic field, intra- and inter-dimer coupling constants. More specifically, the frustrated and modulated quantum antiferromagnetic phases are responsible in zero-temperature magnetization curves for a zero magnetization plateau. The intermediate 1/11- and 5/11-plateaus emerge due to the frustrated and modulated quantum ferrimagnetic phases, while the intermediate 9/11- and 10/11-plateaus can be attributed to the quantum and classical ferrimagnetic phases. It is conjectured that the magnetization plateau experimentally observed in a high-field magnetization curve of 3d-4f heterobimetallic coordination polymer [{Dy(hfac)2(CH3OH)}2{Cu(dmg)(Hdmg)}2]n (H2dmg = dimethylglyoxime; Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) could be attributed to the classical and quantum ferrimagnetic phases.

X-ray Structure and Magnetic Properties of Heterobimetallic Chains Based on the Use of an Octacyanidodicobalt(III) Complex as Metalloligand

The assembly of [Co2III(μ-2,5-dpp)(CN)8]2− anions and [MII(CH3OH)2(DMSO)2]2+ cations resulted into the formation of two heterobimetallic 1D coordination polymers of formula [MII(CH3OH)2(DMSO)2(μ-NC)2Co2III(μ-2,5-dpp)(CN)6]n·4nCH3OH [M = CoII (1)/FeII (2) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine. The [Co2III(μ-2,5-dpp)(CN)8]2− metalloligand coordinates the paramagnetic [MII(CH3OH)2(DMSO)2]2+ complex cations, in a bis-monodentate fashion, to give rise to neutral heterobimetallic chains. Cryomagnetic dc (1.9–300 K) and ac (2.0–13 K) magnetic measurements for 1 and 2 show the presence of Co(II)HS (1) and Fe(II)HS (2) ions (HS – high-spin), respectively, with D values of +53.7(5) (1) and −5.1(3) cm−1 (2) and slow magnetic relaxation for 1, this compound being a new example of SIM with transversal magnetic anisotropy. Low-temperature Q-band EPR study of 1 confirms that D value is positive, which reveals the occurrence of a strong asymmetry in the g-tensors and allows a rough estimation of the E/D ratio, whereas 2 is EPR silent. Theoretical calculations by CASSCF/NEVPT2 on 1 and 2 support the results from magnetometry and EPR. The analysis of the ac magnetic measurements of 1 shows that the relaxation of M takes place in the ground state under external magnetic dc fields through dominant Raman and direct spin-phonon processes.

Zn/Ni and Zn/Pd Heterobimetallic Coordination Polymers with [SSC-N(CH2COO)2]3− Ligands

In the construction of heterobimetallic coordination polymers based on dithiocarbamato–carboxylate (DTCC ligands), platinum as a thiophilic metal center can be replaced by the cheaper nickel or palladium. The compounds Zn[Pd(HL)2] and Zn2[M(L)2] (M = Ni, Pd; L = {SSC-N(CH2COO)2}3−) were prepared in a sequential approach starting from K3(L). The products were characterized by IR and NMR spectroscopy, thermal analyses, and single-crystal X-ray diffraction. The products decompose under nitrogen between 300 and 400 °C. Zn[Pd(HL)2] · 6H2O forms polymeric chains in the solid state, and the Zn2[M(L)2] · 14H2O (M = Ni, Pd) exhibit two-dimensional polymeric structures, each being isotypic with the respective Zn/Pt analogs. While the carboxylate groups in all these products are coordinated to zinc in a κO-monodentate mode, a structural variant of Zn2[Ni(L)2] having κO:κO′-briding carboxylate groups was also obtained. Exchange of the metal sites in the two Ni/Zn compounds was not observed, and these compounds are therefore diamagnetic.

Dithiocarbamatocarboxylate (DTCC) Ligands-Building Blocks for Hard/Soft-Heterobimetallic Coordination Polymers.

Four zinc/platinum(II) heterobimetallic coordination polymers with dithiocarboxylate-functionalized carboxylate (DTCC) ligands were prepared by different synthetic approaches and characterized by elemental analyses, IR and NMR (1H, 13C, and 195Pt) spectroscopy, thermal analyses coupled with mass spectrometry (TG/DTA/MS), and single-crystal and powder X-ray diffraction studies. Sequential syntheses via the carboxylic acid substituted platinum dithiocarbamates and zinc acetate revealed crystalline products in good to excellent yields. One-pot preparations from potassium DTCC salts, K2PtCl4, and ZnCl2 led to comparable products, thus demonstrating the high selectivity of the two donor groups toward platinum(II) and zinc. [SSC-N(Me)CH2COO]2- and [SSC-N(CH2COO)(CH2COOH)]2-, DTCC ligands derived from sarcosine and iminodiacetic acid, respectively, were found to form planar zigzag chains with zinc and platinum(II) ions, while the use of the l-proline-derived ligand [SSC-NC4H7COO]2- results in a helical structure. In the case of [SSC-N(CH2COO)2]3-, two-dimensional arrays are formed. All compounds are thermally stable up to 240-400 °C under nitrogen.

Luminescence behaviour of Au(I)-Cu(I) heterobimetallic coordination polymers based on alkynyl-tris(2-pyridyl)phosphine Au(I) complexes.

A set of alkynyl-tris(2-pyridyl)phosphine Au(i) complexes was synthesized and characterized. Free coordination functions on the ligand environment periphery, namely 'scorpionate' PPy3 and the C[triple bond, length as m-dash]C bond, allowed these ditopic metalloligands to be selectively linked to 1D coordination polymers by reaction with Cu(i), which used both Cu-(N-PPy3) and Cu-(η2-C[triple bond, length as m-dash]C) coordination modes. Single-crystal and powder XRD, NMR, and XPS techniques were used to characterize the coordination polymers obtained. Heterobimetallic Au(i)-Cu(i) coordination polymers demonstrate triplet photoluminescence which was studied by spectroscopic and computational methods to understand the pathway of energy transfer inside the chain of linked chromophore centres. The intriguing feature of the electronic structure of heterobimetallic supramolecular assemblies is the 'long-distance' electronic transition involving PhC2 and PPy3 ligands located at a distance of more than 1 nm from each other. Thus, the assembly of a heterobimetallic coordination polymer from relatively simple 'building blocks' retains the block-wise nature of the electronic structure, but the photophysical properties of the polymer are fundamentally different from the properties of discrete organometallic components.

A Tris(3-pyridyl)stannane as a Building Block for Heterobimetallic Coordination Polymers and Supramolecular Cages.

The systematic assembly of supramolecular arrangements is a persistent challenge in modern coordination chemistry, especially where further aspects of complexity are concerned, as in the case of large molecular mixed-metal arrangements. One targeted approach to such heterometallic complexes is to engineer metal-based donor ligands of the correct geometry to build 3D arrangements upon coordination to other metals. This simple idea has, however, only rarely been applied to main group metal-based ligand systems. Here, we show that the new, bench-stable tris(3-pyridyl)stannane ligand PhSn(3-Py)3 (3-Py=3-pyridyl) provides simple access to a range of heterometallic SnIV /transition metal complexes, and that the presence of weakly coordinating counter anions can be used to build discrete molecular arrangements involving anion encapsulation. This work therefore provides a building strategy in this area, which parallels that of supramolecular transition metal chemistry.

Auxiliary ligand-induced structural diversities of octacyanometalate-based heterobimetallic coordination polymers towards diverse magnetic properties.

Three octacyanometalate-based bimetallic coordination polymers (CPs), {[μ4-MV(CN)8][Co(DMF)4]2(ClO4)}n (M = W CP-1, Mo CP-2) and {[μ4-WIV(CN)8]Co2(azpy)4}n CP-3, were synthesized in the absence (for CPs 1 and 2) or presence (for CP-3) of auxiliary ligand 4,4'-azopyridine (azpy), respectively. CPs 1 and 2 exhibit the same three-dimensional (3D) polymeric cation frameworks with [ClO4]- as the counterions, while CP-3 displays a porous 3D framework in an unusual 2-nodal (4,6)-connected 4,6T155 topology with point symbol as {42·64}{46·64·7·84}2. Notably is that octacyanometalate [WV(CN)8]3- has been reduced into [WIV(CN)8]4- during the synthetic process of CP-3. The magnetic investigations indicate that CP-1 exhibits the typical ferromagnetic property due to the ferromagnetic coupling between W(v) and Co(ii) spin centers, while CP-3 displays the weak ferromagnetic interaction at low temperature, which is consistent with the valence change of W center in CP-3.

Synthesis, structure, and catalytic performance of heterobimetallic coordination polymers with β-diketone containing imidazole group

Four heterobimetallic coordination polymers [Cd[Al(L)3]2(NO3)2 (1), Zn[Al(L)3]2(NO3)2 (2), Zn[Fe(L)3]2(NO3)2 (3), and [ZnFe(L)3Cl](NO3)·3(MeOH)·3(DMF) (4) have been synthesized. The structural analyses of coordination polymers 1–4 showed that they were trigonal space group, among which, coordination polymer 4 was P3 chiral space group. The circular dichroism spectra also confirmed that coordination polymer 4 had chirality. Zn(II) ion in coordination polymer 4 was tetracoordinated, unsaturated, can act as Lewis acid catalyst. Therefore, coordination polymer 4 can catalyze the ring opening of epoxides with aromatic amines to produce β-amino alcohols at room temperature. The catalytic reaction was regioselective, easy to operate, and had good catalyst recovery and repeatability.

One-dimensional oxalato-bridged heterobimetallic coordination polymers by using [the [Cr(pyim)(C2O4)2]− complex as metalloligand [pyim = 2-(2′-pyridyl)imidazole

Four new coordination polymers based on the use of the [Cr(pyim)(C2O4)2]− species as a metalloligand, namely [LiCr(pyim)(C2O4)2(MeOH)]n (1), {[CaCr2(pyim)2(C2O4)4]·2MeOH}n (2), {[SrCr2(pyim)2(C2O4)4(H2O)]·0.45MeOH·4.55H2O}n (3) and {[CdCr2(pyim)2(C2O4)4]·MeOH}n (4) [pyim = 2-(2′-pyridyl)imidazole] have been synthesized and characterized by elemental analyses, IR spectra and X-ray diffraction on single crystals. Complex 1 is a neutral heterobimetallic chain where the tris(chelated) chromium(III) unit acts as a bis-bidentate ligand towards {Li(MeOH)}+ fragments through its two oxalate ligands, each lithium ion being five-coordinate in a intermediate surrounding between square pyramidal and trigonal bipyramidal. The structure of 2 consists of neutral oxalato-bridged chromium(III)-calcium(II) double chains of single chirality [all the tris(chelated) chromium centres have the same chirality either Λ or λ] and methanol molecules of crystallization. Each calcium ion in 2 exhibits a square antiprism environment which is built by four bidentate oxalate ligands from four [Cr(pyim)(C2O4)2]− units. Neutral oxalato-bridged chromium(III)-strontium(II) double chains also occur in 3 with methanol and water molecules of crystallization, each alkaline-earth cation being nine-coordinate in a monocapped square antiprism environment which is defined by a water molecule and eight oxalate-oxygens from four [Cr(pyim)(C2O4)2]− units. The CrIII2MII2 loops [M = Ca (2) and Sr (3)] within each double chain are planar. The structure of 4 is also made of neutral oxalato-bridged chromium(III)-cadmium(II) double chains but in contrast to 2 and 3, the chirality of the tris(chelated) chromium unit in 4 is alternated in each loop and the adjacent CrIII2CdII2 loops are not planar but form a dihedral angle of 84.8°. The potential use of the [Cr(pyim)(C2O4)2]− entity as a metalloligand in designing heterobimetallic compounds is analyzed and discussed.

Novel hetero-bimetallic coordination polymer as a single source of highly dispersed Cu/Ni nanoparticles for efficient photocatalytic water splitting

Monodispersed Cu and Ni nanoparticles are deposited over TiO2 using a hetero-bimetallic coordination polymer for efficient photocatalytic water splitting.

2D and 3D mixed MII/CuII metal-organic frameworks (M = Ca and Sr) with N,N'-2,6-pyridinebis(oxamate) and oxalate: preparation and magneto-structural study.

Three heterobimetallic complexes of formula [Ca2Cu3(mpyba)2(2-apyma)(H2O)7]·8.3H2O (1), [Sr2Cu3(mpyba)2(2-apyma)(H2O)8]·11.6H2O (2) and [Sr4.5Cu4(mpyba)4(ox)(H2O)20]·8.5H2O (3) [H4mpyba = N,N'-2,6-pyridinebis(oxamic acid), 2-apyma = 2-(6-aminopyridinyl)oxamate and ox = oxalate] have been synthesized and structurally characterized. Complexes 1 and 2 are isostructural compounds, with tricopper(ii) units having mpyba and its hydrolytic product (2-apyma) as ligands. They are interlinked through strontium(ii) (1) and calcium(ii) (2) ions to afford neutral two-dimensional networks. Two of the copper(ii) ions are five-coordinate in distorted square pyramidal (Cu3) and trigonal bipyramidal (Cu1) surroundings, whereas the other (Cu2) is six-coordinate in an elongated octahedral environment. The main difference between their structures, apart from the number of water molecules, resides in the nature of the alkaline earth cation coordinated to the oxamate fragments, Sr2+ (1)/Ca2+ (2), which exhibit eight and seven coordination, respectively. The π-π interactions and an extensive network of hydrogen bonds in 1 and 2 lead to supramolecular 3D structures. The relatively small size of their cavities, in the micropore domain, hinders the inclusion of N2 but allows CO2 adsorption (0.45 and 0.52 mmol g-1 for 1 and 2, respectively). The structure of 3 is made up of [3,3] metallacyclophane-type motifs, having the formula [Cu2(mpyba)2(H2O)2]4-. These act as tetrakis(bidentate) ligands towards the strontium(ii) ions (Sr1, Sr2 and Sr3), leading to a sheet-like polymer growing in the bc plane, which extends further along the crystallographic a axis by a bis(chelating) oxalate between the Sr1 atoms. The investigation of the magnetic properties of 1-3 in the temperature range 1.9-300 K shows the occurrence of an overall antiferromagnetic behaviour for 1 and 2 [J12 = J23 = -9.71(2) (1) and -10.81(5) cm-1 (2), with the Hamiltonian being defined as H = -J12S1·S2 - J23S2·S3 + gβH[S1 + S2 + S3], and a ferromagnetic coupling within the dicopper(ii) metallacylophane unit of 3 [J = +1.86(1) cm-1 through the Hamiltonian H = -JS1·S2 + gβH(S1 + S2)]. Simple orbital symmetry considerations (1-3) and the spin polarization mechanism (3) account for the observed magnetic properties.

1D hetero-bimetallic regularly alternated 4f-3d coordination polymers based on N-oxide-4,4'-bipyridine (bipyMO) as a linker: photoluminescence and magnetic properties.

Heterotopic divergent ligand N-oxide-4,4'-bipyridine (bipyMO) has been herein exploited for the preparation of hetero-bimetallic coordination polymers where Ln(hfac)3 and M(hfac)2 nodes regularly alternate (Hhfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione), bipyMO being able to selectively use its two potential coordination sites to discriminate the metal ions. The synthesis of three coordination polymers, [Ln(hfac)3M(hfac)2(bipyMO)2]n (Ln = Eu, M = Zn, 1; Ln = Eu, M = Cu, 2, Ln = Dy, M = Co, 3), was carried out by reacting the appropriate [M(hfac)2(bipyMO)]n and [Ln(hfac)3] precursors in toluene in the presence of a given stoichiometric amount of bipyMO. The products were characterized by elemental analysis, X-ray powder diffraction, and FTIR spectroscopy. Single crystal X-ray diffraction studies carried out on 2 showed that it was formed by chains containing the hexa-coordinated 3d metal (Cu(hfac)2[N]2) and the octa-coordinated lanthanide (Eu(hfac)3[O]2) nodes, where [N] and [O] stand for the donor atom of the bridging divergent ligand. The X-ray powder diffraction patterns of the three compounds and the comparison of their cell constant values allowed establishing that the derivatives were isotypic. Photoluminescence (PL) studies on microcrystalline sample powders evidenced a bright red emission for 1 with an absolute PL quantum yield of 0.24. The sensitized emission of Eu3+ can be excited in a wide wavelength range, from UV to visible, up to ≈450 nm. Conversely, europium emissions are not detectable in 2 due to the presence of Cu(hfac)2(bipyMO) moieties whose strong absorption overlaps Eu3+ transitions. Magnetic measurements conducted on 3 revealed the presence of a weak ferromagnetic interaction below 2.1 K. An ac susceptibility study highlighted a slow relaxation of the magnetization of 3 with an applied static magnetic field of 0.1 T, which could be equally fitted with a Orbach-direct or a Raman-direct mechanism. No relaxation dynamics was detected without the application of a static magnetic field.