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Metal-organic frameworks (MOFs) are promising multifunctional porous materials for biomedical and environmental applications. Here, we report synthesis and characterization of a new MOF based on the tetrahedral secondary building unit [Zn

Metal organic frameworks (MOFs) have received significant attention in recent years in the areas of biomedical and environmental applications. Among them, mixed metal MOFs, although promising, are relatively few in number in comparison with their homometallic analogues. The employment of benzophenone-4,4′-dicarboxylic acid (bphdcH2) in mixed metal MOF chemistry provided access to a 3D MOF, [Na2Zn(bphdc)2(DMF)2]n (NUIG1). NUIG1 displays a new topology and is a rare example of a mixed metal MOF based on 1D rod secondary building units. UV-vis, HPLC, TGA, XRPD, solid state NMR and computational studies indicated that NUIG1 exhibits an exceptionally high Ibuprofen (Ibu) and nitric oxide adsorption capacity. The MCF-7 cell line was used to assess the toxicity of NUIG1 and Ibu@NUIG1, revealing that both species are non-toxic (cell viability > 70%). NUIG1 exhibits good performance in the adsorption of metal ions (CoII, NiII, CuII) from aqueous environments, as was demonstrated by UV-vis, EDX, ICP, SEM and direct and alternate current magnetic susceptibility studies. The colour and the magnetic properties of the M@NUIG1 species depend strongly on the kind and the amount of the encapsulated metal ion in the MOF pores.

The initial employment of methyl 2-pyridyl ketoxime, (py)C(Me)NOH, in mixed metal Ni/Mn cluster chemistry, provided access to complexes [NiII2MnIII{(py)C(Me)NO}6](ClO4) (1) and [NiII2MnIII2{(py)C(Me)NO}6(OMe)2(MeOH)2](ClO4)2 (2) that display a linear and a zig-zag metal arrangement, respectively. 1 and 2 are synthesized by reacting Ni(ClO4)2·6H2O, (py)C(Me)NOH, Mn(ClO4)2·6H2O and NaOMe in different molar ratios (2:6:1:6, 1; 1:3:1:3, 2) in MeOH, and they are the first examples of 3d–3d′ mixed-metal clusters bearing (py)C(Me)NOH. The employment of phenyl 2-pyridyl ketoxime, (py)C(ph)NOH, instead of (py)C(Me)NOH, provided access to the octanuclear homometallic compound [MnII4MnIII4O4(NO3)2{(py)C(ph)NO}8(HCO2)2(MeOH)2] (3) that possesses a double-butterfly {MnII4MnIII4(μ4-O)2(μ3-O)2}12+ core. 3 joins the small family of Mn/(py)C(ph)NO− clusters. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on 1 and 2 and revealed the presence of antiferromagnetic exchange interactions between the metal ions (JMn–Ni = −6.34 ± 0.14 cm−1 in 1; JMn–Ni = −4.57 ± 0.08 cm−1, JMn–Mn = −12.72 ± 0.12 in 2) and a diamagnetic ground state for both compounds.

The initial study of the ligand blend pyridine-2-amidoxime (pyaoxH2)/1,4-benzenedicarboxylic (H2bdc) or 1,3,5-benzenetricarboxylic acid (H3btc) provided access to four 1D coordination polymers, [Zn(bdc)(pyaoxH2)(DMF)]n (1), {[Ni(bdc)(pyaoxH2)2]·2DMF}n (2·2DMF), {[Mn(bdc)(pyaoxH2)2]·2DMF}n (3·2DMF) and [Ni(Hbtc)(pyaoxH2)2]n (5), and the discrete (0D) compound [Ni(H2btc)2(pyaoxH2)2]·2H2O (4·2H2O), whose further polymerization yielded 5. These compounds are the first metal coordination polymers bearing pyaoxH2 and rare examples of such species with any type of a 2-pyridyl oxime. The crystal structures of the compounds have been determined by single crystal X-ray crystallography, whereas their identity, purity and stability were confirmed by pxrd studies. Thermal stability studies were performed in 1, 2·2DMF, 4·2H2O and 5. The photoluminescence properties of 1 have been studied and revealed a maximum emission peak at 440 nm and a visible shoulder at 467 nm, assigned to the pyaoxH2 and bdc2− ligands, respectively.

The synthesis, structural characterization and magnetic study of novel CoII/4f and CoII/YIII clusters are described. In particular, the initial employment of di-2-pyridyl ketone, (py)2CO, in mixed metal Co/4f chemistry, provided access to four triangular clusters, [CoII2MIII{(py)2C(OEt)(O)}4(NO3)(H2O)]2[M(NO3)5](ClO4)2 (M = Gd, 1, Dy, 2, Tb, 3, Y, 4), where (py)2C(OEt)(O)&minus, is the monoanion of the hemiketal form of (py)2CO. Clusters 1&ndash, 4 are the first reported Co/4f (1&ndash, 3) and Co/Y (4) species bearing (py)2CO or its derivatives, despite the fact that over 200 metal clusters bearing this ligand have been reported so far. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on 1&ndash, 4 and revealed the presence of weak ferromagnetic exchange interactions between the metal ions (JCo-Co = +1.3 and +0.40 cm&minus, 1 in 1 and 4, respectively, JCo-Gd = +0.09 cm&minus, 1 in 1). The ac susceptibility studies on 2 revealed nonzero, weak out-of-phase (&chi, &rsquo, M) signals below ~5 K.

The use of pyridine-2-amidoxime (pyaoxH2) in Ni chemistry has provided access to a dodecanuclear complex and a hexadecanuclear Ni cluster, namely [Ni12(pyaox)6(pyaoxH)6(MeOH)2Cl2]Cl4·5MeOH (1·5MeOH) and [Ni16(pyaox)8(pyaoxH)8(MeOH)4](SO4)4·10H2O·26MeOH (2·10H2O·26MeOH). Complex 1·5MeOH was isolated by the reaction of NiCl2·6H2O, pyaoxH2 and NaOMe in a 1 : 1 : 2 molar ratio in MeOH in 60% yield. Treatment of NiSO4·6H2O with pyaoxH2 and NEt3 in a 1 : 1 : 2 molar ratio in MeOH afforded 2·10H2O·26MeOH in good yield (65%). The two compounds display a multi-decker configuration based on stacked Ni4 layers, {Ni4(pyaox)2(pyaoxH)2}2+x (x = 3, 1·5MeOH; x = 4, 2·10H2O·26MeOH); each deck consists of two square planar and two octahedral NiII centres. The number of decks observed in 1·5MeOH and 2·10H2O·26MeOH depends on the nature of the inorganic anion that is present in the reaction system, which provides elements of synthetic control towards new high nuclearity NiII species. 2·10H2O·26MeOH is the first structurally characterized complex of any metal displaying a quadruple-decker configuration, being also the highest nuclearity metal cluster bearing pyaoxH2 and the highest nuclearity NiII cluster with any type of 2-pyridyl oxime. Each cluster cation displays ferromagnetic exchange between the octahedral NiII ions resulting in a spin ground state of S = 6 for 1 and S = 8 for 2. Magnetothermal studies have been performed and discussed for both clusters., CP and CE thank the School of Chemistry, NUI Galway, for the financial support. RI thanks the Royal Society of Edinburgh and ME thanks Spanish MINECO (MAT2015-68204-R) for funding. LCS acknowledges the financial support by FEDER (Fundo Europeu de Desenvolvimento Regional) through PT2020, by FCT (Fundação para a Ciência e a Tecnologia) for the research centre REQUIMTE/LAQV (UID/QUI/50006/2013) and for the grant SFRH/BPD/111899/2015.

The importance of 3d/4f-metal cluster chemistry is outlined, and the employment of 2-pyridyl ketone- and 2-pyridyl oxime-based ligands for the preparation of low-nuclearity NiII/LnIII complexes (Ln = lanthanide) is reviewed. The synthetic utility of the “metal complexes as ligands” and “one-pot” approaches is critically discussed. The small nuclearity of the products permits the in-depth analysis of their magnetic properties.

The use of pyridine-2-amidoxime (pyaoxH

The combined use of di-2-pyridyl ketone, (py)(2)CO, and acetates (MeCO2-) in nickel(II) chemistry in H2O-MeCN under basic conditions (Et3N) afforded the coordination cluster [ Ni-11(OH)(6)(O2CMe)(12){(py)(2)C(OH)(O)}(4)(H2O)(2)] (1) in 80% yield, where (py)(2)C(OH)(O)(-) is the monoanion of the gem-diol form of (py)(2)CO. The complex contains a novel core topology. The core of 1 comprises a central non-linear {Ni-3(mu(2)-OH)(4)}(2+) subunit which is connected to two cubane {Ni-4(OH)(mu(3)-OR)(2)(mu(3)-OR')}(4+) subunits [RO- = (py)(2)C(OH)(O)(-) and R'O- = MeCO2-] via the OH- groups of the former which become mu(3). The linkage of the Ni3 subunit to each Ni-4 subunit is completed by two eta(1):eta(1):mu(2) and one eta(1):eta(3):mu(4) MeCO2- groups. Peripheral ligation is provided by two terminal monodentate MeCO2- and two terminal aqua ligands. The (py)(2)C(OH)(O)(-) ligands adopt the eta(1):eta(1):eta(3):mu(3) coordination mode. From the twelve MeCO2- ligands, two are eta(1), two eta(1):eta(3):mu(4) and eight adopt the syn, syn eta(1):eta(1):mu(2) coordination mode; four of the latter bridge NiII centers at opposite faces of the cubane subunits. Complex 1 is the largest nickel(II)/(py)(2)CO-based ligand coordination cluster discovered to date and has an extremely rare nuclearity (Ni-11) in the cluster chemistry of nickel(II). Variable-temperature, solid state dc susceptibility, and variable-field magnetization studies at low temperatures were carried out on complex 1. The study of the data reveals an S = 3 ground state, which has been well rationalized in terms of known magnetostructural correlations and the structural features of 1. An attempt has also been made to interpret the magnetic properties of the undecanuclear cluster in a quantitative manner using four exchange interaction parameters and the obtained J values are discussed. The role of H2O in the solvent medium that led to 1, and the high nickel(II) and acetate to di-2-pyridyl ketone reaction ratio employed for its preparation, on the nuclearity and identity of the cluster are critically analyzed.

Nucleophilic attack by the carbanion C ¯ H 2 COCH 3 at the carbonyl atom of di-2-pyridyl ketone, (py)2CO, in the presence of NiII under basic conditions has yielded the cationic cluster [Ni4{(py)2C(CH2COCH3)(O)}4](ClO4)4 (1). The cluster cation possesses a distorted cubane {Ni4(μ3-OR′)4}4+ core resulting from the η1:η3:η1:η1:μ3 coordination mode of the in situ formed ligand and has a diamagnetic ground state.

The preparation and crystal structure of a tetranuclear Ni(II) sulfato cluster containing the anion of di-2-pyridyl ketone oxime, (py)2CNO−, are reported. Treatment of NiSO4·6H2O with one equivalent of (py)2CNOH and one equivalent of NEt3 in MeOH leads to the compound [Ni4{(py)2CNO}4(SO4)2(MeOH)4] (1) in moderate yield. The metal ions are linked together by two 3.2111 and two 2.1110 (Harris notation) (py)2CNO− ligands, as well as two 2.1100 SO42− ions to create a rare metallacrown-type (12-MC-4) ring. Strong H-bond intermolecular interactions in 1 lead to the formation of a 1D chain along the axis. Characteristic IR bands are discussed in terms of the known structure of 1.

The reactions of representative 2-pyridyl oximes with NiII salts in the presence of a base have been investigated. The synthetic study has led to the new triangular complexes [Νi3(ppko)6]·2H2O·0.5EtOH·MeOH (1·2H2O·0.5EtOH·MeOH), [Νi3(mpko)3(HCO2)2(mpkoH)2](ClO4) (2) and [Νi3(ppko)3(HCO2)2(ppkoH)2](ClO4) (3), where ppko− is the anion of phenyl(2-pyridyl)ketone oxime and mpko− is the anion of methyl(2-pyridyl)ketone oxime. The structures of compounds 1 and 2 have been determined by single crystal X-ray diffraction. The ppko− ligand in 1 adopts four different coordination modes including the unique NpyridylOoximate chelating one which gives rise to a 6-membered chelating ring, while the neutral and the deprotonated oxime ligands in 2 adopt three different coordination modes. The magnetic properties of 1 and 2 have been studied by variable-temperature dc magnetic susceptibility techniques which indicate antiferromagnetic interactions.

The preparation and crystal structure of a hexanuclear Ni(II) sulfato cluster containing the anion of phenyl(2-pyridyl)ketone oxime, (py)C(ph)NO − , is reported. Treatment of NiSO 4 ·6H 2 O with 1 equiv. of (py)C(ph)NOH and 1 equiv. of NaOMe in DMF under reflux leads to the compound [Νi 6 (SO 4 ) 2 {(py)C(ph)NO} 8 ] · 6DMF ( 1· 6DMF) in moderate yield. The metal ions are linked together by two 3.211 (Harris notation) (py)C(ph)NO − ligands, six 2.111 (py)C(ph)NO − ligands and two 5.2210 SO 4 2 - ions. Its skeleton consists of six Ni II ions arranged in a chair conformation. Compound 1 joins a small family of structurally characterized metal complexes containing the neutral or anionic forms of phenyl(2-pyridyl)ketone oxime as ligands, and it is a rare example in which the SO 4 2 - ions are coordinated in the 5.2210 fashion. Characteristic IR bands are discussed in terms of the known structure of 1 . Its magnetic properties have been studied by variable-temperature dc magnetic susceptibility techniques which indicate competitive antiferromagnetic interactions within its triangular subunits.

The reactions of 2-(hydromethyl)pyridine, hmpH, with Ni(O2CMe)2·4H2O in H2O, in the absence of counterions, have been investigated. The synthetic study has led to the two new complexes [Ni(O2CMe)2(hmpH)2] (1) and [Ni4(O2CMe)4(hmp)4(H2O)2] (2). Complex 1 can also be transformed into 2 by reacting with an excess of NaOH in H2O. The structures of 1 and 2·2.25H2O·0.5(1,4-dioxane) have been solved by single-crystal, X-ray crystallography. The octahedral NiII center in centrosymmetric 1 is coordinated by two 1.10 (Harris notation) MeCO2− groups and two N,O-chelating (1.11) hpmH ligands. The tetranuclear cluster molecule of 2·2.25H2O·0.5(1,4-dioxane) possesses a distorted cubane {Ni4(μ3-OR′)4}4+ core [R′ = (2-pyridyl)CH2–] with the NiII ions and the oxygen atoms from the 3.31 hmp− ligands occupying alternate vertices of the cube. Two 2.11 MeCO2− groups cap two opposite faces of the cube, while two 1.10 MeCO2− ions and two aqua ligands complete the octahedral coordination sphere of the metal centers. Characteristic IR bands for the two complexes are discussed in terms of the nature of bonding and the structures of the two complexes. The variable-temperature magnetic properties of 2 have been modeled with two J values, and reveal antiferromagnetic exchange interactions between the four NiII ions to give a diamagnetic ground state.

Employing the mononuclear complex [Ni{(py)C(Me)NO}2{(py)C(Me)NOH}] (1) as ‘ligand’ [(py)C(Me)NOH = methyl 2-pyridyl ketone oxime], the use of the ‘metal complexes as ligands’ approach has led to the synthesis of the mixed NiII/LnIII complexes [NiTb{(py)C(Me)NO}2(NO3)3{(py)C(Me)NOH}] (2), [Ni2Ln2{(py)C(Me)NO}6(NO3)4] (Ln = Dy, 3; Ln = Tb, 4) and [Ni2Tb{(py)C(Me)NO}6](NO3) (5). The structures of 2, 3, and 5, and the magnetic properties of 2 and 5 are briefly discussed.

A general method of increasing the ground-state total spin value of a polynuclear 3d-metal complex is illustrated through selected examples from cobalt(II) and nickel(II) cluster chemistry that involves the dianion of the gem-diol form of di-2-pyridyl ketone and carboxylate ions as organic ligands. The approach is based on the replacement of hydroxo bridges, that most often propagate antiferromagnetic exchange interactions, by the end-on azido ligand, which is a ferromagnetic coupler.

The use of di-2-pyridyl ketone ((py)2CO)/sulfate “blend” in nickel and zinc chemistry has yielded the neutral cubane clusters [Ni4(SO4)2{(py)2C(OH)O}4]·4MeOH·3H2O (1·4MeOH·3H2O) and [Zn4 (SO4)2{(py)2C(OH)O}4 (H2O)2]·6H2O (2·6H2O). The preparation of the two complexes was achieved by the reaction of MSO4·×H2O [M = Ni, x = 6 (1); M = Zn, x = 7 (2)] with (py)2CO and LiOH·H2O in MeOH/H2O (for both complexes) or MeOH/MeCN (only for 1). The structures of both compounds have been determined by single-crystal X-ray crystallography. Di-2-pyridyl ketone exists in its monoanionic gem-diol form and functions as an η1:η3:η1:μ3 ligand. Both complexes have been characterized by spectroscopic techniques (IR, Raman). Thermal decomposition (TG, DTG and DTA) data for 2 are also discussed. The magnetic properties of 1 have been studied by variable-temperature dc magnetic susceptibility techniques. The studies indicate both ferromagnetic and antiferromagnetic coupling between the four NiII atoms. A three-J model was found to be adequate for describing the thermal variation of the molar magnetic susceptibility.

The further use of di-2-pyridyl ketone [(2-py) 2 CO] in nickel(II) acetate chemistry has been investigated. Various synthetic procedures have led to the synthesis of complexes [Ni 4 (O 2 CMe) 2 ((2-py) 2 C(OH)O} 4 (H 2 O) 2 ](ClO 4 ) 2 (1), [Ni(O 2 CMe){(2-py) 2 C(OH) 2 }{(2-py) 2 CO}](ClO 4 )·H 2 O (2. H 2 O), [Ni 4 (O 2 CMe) 3 {(2-py) 2 C(OH)O} 4 ](ClO 4 )·2H 2 O·2EtOH (3·2H 2 O·2EtOH), [Ni 4 (O 2 CMe) 4 ((2-py) 2 C(OH)O} 4 ]·2MeCN (4·2MeCN), and [Ni4(O 2 CMe) 3 ((2-py) 2 C(OH)O} 4 ](O 2 CMe)· 6H 2 O·MeCN (5·6H 2 O·MeCN). The Ni II -mediated hydrolysis of (2-py) 2 CO to give the coordinated molecule (2-py) 2 C(OH) 2 or the monoanion (2-py) 2 C(OH)O - involves nucleophilic attack by H 2 O on the carbonyl group. The Ni II ion in 2·H 2 O is coordinated by one monodentate acetate, one N,N',O-tridentate chelating (2-py) 2 C(OH) 2 molecule, and one N,N'-bidentate chelating (2-py) 2 CO ligand. The tetranuclear cluster cation of 1 has a cubane (Ni 4 (μ 3 -OR) 4 } 4+ core with Ni II ions and deprotonated oxygen atoms occupying alternate vertices. The [Ni 4 (O 2 CMe) 3 {(2-py) 2 C(OH)O} 4 ] + cations present in the complexes 3·2H 2 O·2EtOH and 5·6H 2 O·MeCN have almost identical cubane structures that are different from the structure of the cation of 1. The four metal ions in the centrosymmetric molecules of 4-2MeCN are located at four vertices of a defect dicubane (with two missing vertices) and are bridged by six oxygen atoms. Characteristic IR bands are discussed in terms of the known structures of 1-5. The magnetic data for the Ni II cubane 1 has been modeled with two J values, and shows that the coupling consists of two ferromagnetically coupled pairs that are antiferromagnetically coupled to give a diamagnetic ground state. The magnetic properties of 4 have been modeled with three J values, and reveal competing antiferromagnetic and ferromagnetic coupling between the four N II ions.

The initial employment of 2-pyridinealdoxime in 3d/4f chemistry has led to a Ni(II)(8)Dy(III)(8) cluster with an unprecedented metal topology; the compound has an unusual structure, is the highest-nuclearity metal oxime cluster to date, and exhibits slow magnetization relaxation.

The importance of 3d/4f-metal cluster chemistry is outlined, and the employment of 2-pyridyl ketone- and 2-pyridyl oxime-based ligands for the preparation of low-nuclearity Ni II /Ln III complexes (Ln = lanthanide) is reviewed. The synthetic utility of the "metal com- plexes as ligands" and "one-pot" approaches is critically discussed. The small nuclearity of the products permits the in-depth analysis of their magnetic properties.

The coordination chemistry of di-2-pyridyl ketone and related ligands is reviewed. An outline of the variety of such ligands is presented. References are given to methods for the synthesis of ligands that are not available on the market. The activation of the carbonyl group(s) of some of the ligands towards further reactions seems to be an emergent area of synthetic inorganic chemistry. The coordination chemistry of each ligand with metals is briefly described. Emphasis is placed on structural features and physical properties (mainly magnetic) of the resulting metal clusters and coordination polymers. The structural diversity of the complexes stems from the ability of the deprotonated diol- or hemiketal-type ligands to adopt a variety of bridging coordination modes depending on the number of carbonyl groups, the nature of the extra donor groups in the molecule and on the reaction conditions. Employment of a second organic or inorganic ligand in this chemistry gives an extraordinary structural flexibility in the resulting mixed-ligand systems. The initial use of 1,1′-carbonyldiimidazole and 1,1′-oxalyldiimidazole in copper(II) chemistry, which leads to unprecedented coordination polymers containing alcoholysis and/or hydrolysis “fragments” of the ligands, is also illustrated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A general method of increasing the ground-state total spin value of a polynuclear 3d-metal complex is illustrated through selected examples from cobalt(II) and nickel(II) cluster chemistry that involves the dianion of the gem-diol form of di-2-pyridyl ketone and carboxylate ions as organic ligands. The approach is based on the replacement of hydroxo bridges, that most often propagate antiferromagnetic exchange interactions, by the end-on azido ligand, which is a ferromagnetic coupler. (c) 2006 Elsevier Ltd. All rights reserved.

Using monoanionic forms of di-2-pyridyl ketone as the only primary ligand, triangular Ni(2)M (M = lanthanide, Y) complexes with interesting magnetic properties have been synthesized.

The coordination chemistry of di-2-pyridyl ketone and related ligands is reviewed. An outline of the variety of such ligands is presented. References are given to methods for the synthesis of ligands that are not available on the market. The activation of the carbonyl group(s) of some of the ligands towards further reactions seems to be an emergent area of synthetic inorganic chemistry. The coordination chemistry of each ligand with metals is briefly described. Emphasis is placed on structural features and physical properties (mainly magnetic) of the resulting metal clusters and coordination polymers. The structural diversity of the complexes stems from the ability of the deprotonated diol- or hemiketal-type ligands to adopt a variety of bridging coordination modes depending on the number of carbonyl groups, the nature of the extra donor groups in the molecule and on the reaction conditions. Employment of a second organic or inorganic ligand in this chemistry gives an extraordinary structural flexibility in the resulting mixed-ligand systems. The initial use of 1,1′-carbonyldiimidazole and 1,1′-oxalyldiimidazole in copper(II) chemistry, which leads to unprecedented coordination polymers containing alcoholysis and/or hydrolysis “fragments” of the ligands, is also illustrated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)