Random Co(II)-Ni(II) Ferromagnetic Chains Showing Coexistent Antiferromagnetism, Metamagnetism, and Single-Chain Magnetism.

A series of isomorphous compounds of general formula [Co1- xNi x(tzpo)(N3)(H2O)2] n· nH2O ( x = 0, 0.19, 0.38, 0.53, 0.68, 0.84, and 1; tzpo = 4-(5-tetrazolate)pyridine- N-oxide) was prepared. The compounds consist of homometallic or heterometallic chains with simultaneous azide-tetrazolate bridges. The heterometallic systems feature random distribution of metal ions. All compounds across the series exhibit intrachain ferromagnetic coupling, interchain antiferromagnetic (AF) ordering, field-induced metamagnetic transition, and, except the Ni-only compound, single-chain magnetic dynamics. The AF ordering temperature, the metamagnetic critical field, and the relaxation parameters show different composition dependence. Notably, the blocking temperature for the Co-rich materials is higher than the Co-only compound, suggesting synergy between the randomly distributed Co(II) and Ni(II) ions in promoting slow relaxation. The results imply rich physics in the random mixed-metal systems and demonstrate the possibility of improving single-chain relaxation properties by blending metal ions.

Magnetic coupling and slow relaxation of magnetization in chain-based Mn(II), Co(II), and Ni(II) coordination frameworks.

Three isomorphous coordination polymers based on the chain with triple (µ-1,1-N3)(µ-1,3-COO)2 bridges have been synthesized from a new zwitterionic dicarboxylate ligand [L(-) = 1-(4-carboxylatobenzyl)pyridinium-4-carboxylate]. They are of formula [M(L)(N3)]n·3nH2O [M = Mn(II), Co(II), and Ni(II)]. In these compounds, the mixed-bridge chains are linked into 2D coordination networks by the N-benzylpyridinium spacers. The magnetic properties depend strongly on the nature of the metal center. The magnetic coupling through (µ-1,1-N3)(µ-1,3-COO)2 is antiferromagnetic in the Mn(II) compound but ferromagnetic in the Co(II) and Ni(II) analogues. Magnetostructural analyses indicate that the magnitude of the magnetic coupling can be correlated to the M-N-M angle of the azide bridge and the average M-O-C-O torsion angle of the carboxylate bridge. As the values of these parameters increase, the antiferromagnetic coupling for Mn(II) decreases while the ferromagnetic coupling for Co(II) increases. With strong magnetic anisotropy, the Co(II) compound behaves as a single-chain magnet showing hysteresis and Glauber-type slow dynamics probably in the infinite-chain region, with Δ(τ)/k = 86 K, Δ(ξ)/k = 26 K, and Δ(A)/k = 34 K. With weaker anisotropy, the Ni(II) species shows slow relaxation of magnetization at much lower temperature.

Tricomponent azide, tetrazolate, and carboxylate cobridging magnetic systems: ferromagnetic coupling, metamagnetism, and single-chain magnetism.

Three novel coordination polymers with azide and a bifunctional zwitterionic ligand bearing carboxylate and tetrazolate as bridging groups, [M(L)(N(3))]·xH(2)O [L=1-(carboxylatomethyl)-4-(5-tetrazolato)pyridinium, M=Cu (1, x=2), Ni (2, x=1), and Co (3, x=1)], have been synthesized and characterized by X-ray crystallography and magnetic measurements. The compounds consist of two-dimensional coordination layers in which uniform anionic chains with the unprecedented tricomponent (µ-azide)(µ-tetrazolate)(µ-carboxylate) bridges are cross-linked by cationic 1-methylenepyridinium spacers. The tricomponent bridges induce ferromagnetic interactions in all the compounds. Furthermore, this isostructural series of ferromagnetic-chain-based compounds has allowed us to observe distinct bulk properties that are dependent upon the natures of the different spin carriers: with the isotropic Cu(II) ion, 1 exhibits a paramagnetic phase of the ferromagnetic chains without long-range magnetic order above 2 K; with the weakly anisotropic Ni(II) ions, 2 displays antiferromagnetic ordering and field-induced metamagnetism without slow dynamic relaxation; and with Co(II), which has strong magnetic anisotropy due to first-order spin-orbital coupling, 3 exhibits magnetic hysteresis and slow magnetization dynamics typical of single-chain magnets.

Magnetic systems with mixed carboxylate and azide bridges: slow relaxation in Co(II) metamagnet and spin frustration in Mn(II) compound.

Two coordination polymers formulated as [{[Co(2)(L)(N(3))(4)]·2DMF}(n) (1) and [Mn(2)(L)(H(2)O)(0.5)(N(3))(8)](n) (2) (L = 1,4-bis(4-carboxylatopyridinium-1-methyl)benzene) were synthesized and structurally and magnetically characterized. In compound 1, the anionic uniform Co(II) chains with mixed (µ-EO-N(3))(2)(µ-COO) triple bridges (EO = end-on) are cross-linked by the cationic bis(pyridinium) spacers to generate 2D coordination layers. It was demonstrated that the triple bridges mediate ferromagnetic coupling and that the compound represents a new example of the rare systems exhibiting the coexistence of antiferromagnetic ordering, metamagnetism, and slow magnetic dynamics. Compound 2 features the magnetic Δ-chain formed from isosceles triangular units with single µ-EE-N(3) and double (µ-EO-N(3))(µ-COO) bridges (EE = end-to-end). The Δ-chains are interlinked by long organic ligands into a 3D framework with novel net topology and 3-fold interpenetration. The magnetic properties of 2 indicate the presence of spin frustration characteristic of Δ-chains with antiferromagnetic interactions.

Novel three-dimensional metal-azide network induced by a bipyridine-based zwitterionic monocarboxylate ligand: structures and magnetism.

The 4,4'-bipyridine-based zwitterionic monocarboxylate ligand, 4,4'-dipyridinio-1-acetate (L), is used as coligand to construct novel magnetic coordination polymers with mixed azide and carboxylate bridges. Two compounds, [Co(2)(L)(2)(N(3))(4)(H(2)O)] x 4 H(2)O (1) and [Mn(6)(L)(4)(N(3))(12)(H(2)O)] x 5 H(2)O (2), have been structurally and magnetically characterized. Compound 1 consists of one-dimensional (1D) coordination chains in which the unprecedented binuclear motifs with mixed (mu-EO-N(3))(mu-COO)(2) (EO = end-on) triple bridges are cross-linked by the 4,4'-dipyridinium-N-methylene spacers. In compound 2, the azide anions link the metal ions into a very complicated three-dimensional (3D) network with unprecedented topology, and the zwitterionic coligand is embedded in and serves as additional supports for the 3D network. Magnetic studies reveal that the mixed (mu-EO-N(3))(mu-COO)(2) triple bridges transmit ferromagnetic coupling in the Co(II) compound, and the overall antiferromagnetic interactions exist in the Mn(II) compound.

2,2'-[1-(2,4,6-Trichlorophenyl)-1H-1,2,4-triazole-3,5-diyl]diphenol.

The title compound, C(20)H(12)Cl(3)N(3)O(2), was synthesized by the reaction of 2-(2-hydroxy-phen-yl)benz[e][1,3]oxazin-4-one with 2,4,6-trichloro-phenyl-hydrazine in ethanol. The trichloro-phenyl ring is nearly perpendicular to the triazole plane [dihedral angle 80.56 (8)°], whereas the two hydroxy-phenyl rings are approximately coplanar with the triazole ring [dihedral angles of 2.79 (12) and 8.00 (14)°]. Intra-molecular O-H⋯N hydrogen bonding is observed between the hydroxy-phenyl and triazole rings.

Decacarbonyl-1κC,2κC,3κC-µ-hydrido-1:2κH:H-(µ-quinoline-2-thiol-ato-1:2κS:S)diosmium(I)osmium(0)(3 Os-Os).

The title compound, [Os(3)(C(9)H(6)NS)H(CO)(10)], contains a nearly equilateral triangle of Os atoms. Two of the Os atoms are bridged by an S atom of the quinoline-2-thiol-ate ligand. Ten carbonyl groups complete the cluster, resulting in a distorted octa-hedral geometry for each Os atom. The hydride atom, which was located in a difference Fourier map and refined isotropically, bridges the shortest Os-Os edge.

Poly[diaqua-bis(µ-azido-κN:N)bis-(µ(3)-1-oxoisonicotinato-κO:O':O'')dicadmium(II)].

In the title compound, [Cd(2)(C(6)H(4)NO(3))(2)(N(3))(2)(H(2)O)(2)](n), one Cd(II) atom is located on an inversion center and is coordinated by four O atoms from four bridging 1-oxoisonicotinate ligands and two N atoms of two bridging azide ligands in a slightly distorted octa-hedral geometry. The other Cd(II) atom, also lying on an inversion center, is coordinated by four O atoms from two bridging 1-oxoisonicotinate ligands and two water mol-ecules and two N atoms of two bridging azide ligands in a slightly distorted octa-hedral geometry. The Cd atoms are connected via the 1-oxoisonicotinate and azide ligands into a two-dimensional coordination network. The crystal structure involves O-H⋯N and O-H⋯O hydrogen bonds.

Diaqua-bis[3-(2-hydroxy-ethyl)-2-methyl-4-oxopyrido[1,2-a]pyrimidin-9-olato-κN,O]manganese(II).

The title compound, [Mn(C(11)H(11)N(2)O(3))(2)(H(2)O)(2)], consists of discrete mononuclear complex mol-ecules. The Mn(II) atom is located on an inversion center and coordinated by two N atoms and two O atoms, each pair in a trans mode, from two 3-(2-hydroxy-ethyl)-2-methyl-4-oxopyrido[1,2-a]pyrimidin-9-olate ligands and by two water mol-ecules. The coordination geometry around the Mn(II) atom is slightly distorted octa-hedral. Mol-ecules are linked by O-H⋯O hydrogen bonds into a three-dimensional network.

Poly[(µ(6)-benzene-1,2,4,5-tetra-carboxyl-ato)bis-(1,10-phenanthroline-κN,N')dimanganese(II)].

The title polymeric compound, [Mn(2)(C(10)H(2)O(8))(C(12)H(8)N(2))(2)](n), was obtained by the reaction of manganese(II) chloride tetra-hydrate with benzene-1,2,4,5-tetra-carboxylic acid (H(4)bta) in aqueous solution. Each Mn(2+) ion is coordinated in a distorted octa-hedral geometry by two N atoms from one 1,10-phenanthroline ligand and four O atoms [Mn-O = 2.116 (2)-2.237 (2) Å] from three bta(4-) ligands, which also act as bridging groups between the Mn(2+) ions.

1,3-Bis[5-(2-pyrid-yl)-1H-tetra-zol-1-yl]propane.

The title compound, C(15)H(14)N(10), is a multidentate ligand obtained by the reaction of 5-(2-pyrid-yl)tetra-zole with 1,3-dibromo-propane. The mol-ecule consists of two 5-(2-pyrid-yl)-1H-tetra-zol-1-yl units connected by a propyl-ene bridge in a U-like conformation. A twofold rotation axis passes through the central C atom.

Random mixed-metal Co1-xNix single-chain magnets with simultaneous azide, carboxylate and tetrazolate bridges.

This paper reports the magnetic properties of a series of isomorphous metal-organic frameworks based on random heterometallic Co1-xNix chains with simultaneous azide, carboxylate and tetrazolate bridges. All the mixed-metal compounds show intrachain FM interactions, field-induced metamagnetism, and SCM-like slow magnetic relaxation. These behaviors are quite different from the parent Co(ii) and Ni(ii) materials, and even a small amount of metal replacement can cause significant magnetic changes. The static properties such as AF ordering, metamagnetic critical field and the hysteresis parameters show complicated composition dependence. Most interestingly, the mixed-metal systems can show a higher blocking temperature than the Co(ii) compound, suggesting that the randomly distributed metal ions have synergistic effects on slow relaxation of magnetization. This is phenomenologically associated with the competitive effects of Δτ and τo.

Diaqua-bis(picolinato N-oxide-κO,O')zinc(II).

In the title compound, [Zn(C(6)H(4)NO(3))(2)(H(2)O)(2)], the Zn atom is located on a centre of inversion and shows a distorted octa-hedral coordination geometry. Two aqua ligands occupy the axial positions and four O atoms of the two chelating picolinic acid N-oxide ligands are located in the equatorial plane. Inter-molecular hydrogen bonds between aqua ligands and organic ligands link mol-ecules into a two-dimensional arrangement.

Field-modified multiple slow relaxations in a metamagnet composed of cobalt(II) chains with mixed azide and tetrazolate bridges.

The title heterobridge system exhibits the coexistence of AF ordering, SCM-derived multi-relaxation dynamics, field-induced metamagnetism and field-induced spin-glass-like dynamics.

Structures and magnetic properties of copper(II) and manganese(II) polymers derived from pseudohalides and a flexible zwitterionic dicarboxylate ligand.

The flexible zwitterionic dicarboxylate ligand 1,4-bis(4-carboxylato-1-pyridinium)butane (bcpb) assumes different conformations to collaborate with pseudohalides in various coordination modes to produce coordination polymers in which distinct anionic motifs with mixed carboxylate and pseudohalide bridges are interlinked by the cationic butylenebis(pyridinium) tethers. The Cu(II) compound, [Cu2(bcpb)(N3)4]n·nH2O (1), is a 1D coordination polymer based on the defective dicubane-like [Cu4(µ3-1,1,1-N3)2(µ-1,1-N3)2(µ-1,1-OCO)2] cluster. With Mn(II), four distinct 3D coordination polymers, [Mn4(bcpb)4(N3)(H2O)4]n(ClO4)7n·nCH3OH·3nH2O (2), [Mn2.5(bcpb)(N3)5(H2O)2]n (3), [Mn2(bcpb)(N3)4]n·nH2O (4), and [Mn2(bcpb)(NCO)4]n·nH2O (5), were characterized. 2 is the first Mn(II) compound with the rare µ4-1,1,3,3 azide bridge and exhibits an unusual 3D framework based on the [Mn4(µ4-1,1,3,3-N3)(µ-1,3-OCO)6] cluster. In 3, the unique undulated honeycomb-like [Mn2(µ-1,3-N3)3]n layers are interlinked into a 3D framework by disordered [Mn(µ-1,1-N3)4(µ-1,3-OCO)2] and [(O(aqua)-H)2···OCO]2 moieties, and the bcpb ligands serve as additional interlayer linkers to lead to the rare self-catenated 6(6) net. 4 and 5 show 3-fold interpenetrated 3D frameworks based on the chains with (µ-1,1-N3)2(µ-1,3-OCO) and (µ-N,N-NCO)2(µ-1,3-OCO) bridges, respectively. Magnetic studies indicated that 1 shows competing ferromagnetic and antiferromagnetic interactions. Compounds 2-5 all show antiferromagnetic coupling between Mn(ii) ions, while 3 shows 3D ordering. Analyses of magneto-structural data suggest a general trend that the antiferromagnetic interaction through (µ-1,1-N3)2(µ-1,3-OCO) or (µ-N,N-NCO)2(µ-1,3-OCO) increases with a decrease of the Mn···Mn distance.

Diverse manganese(II) coordination polymers derived from achiral/chiral imidazolium-carboxylate zwitterions and azide: structure and magnetic properties.

Five Mn(II) coordination polymers containing azide and carboxylate as simultaneous bridges have been derived from different imidazolium-carboxylate zwitterionic ligands: 1-methyl-3-(carboxylatomethyl)imidazolium (L(1)), 1,3-bis(carboxylatomethyl)imidazolium (L(2)), (S,S)-, (R,R)-, and (R,S)-1,3-bis(1-carboxylatoethyl)imidazolium (S,S-L(3), R,R-L(3) and R,S-L(3)). The compounds are formulated as [Mn(L(1))(N3)2] (1), [Mn(L(2))(N3)] (2), [Mn(R,R-L(3))(N3)]·0.5CH3OH (3-R), [Mn(S,S-L(3))(N3)]·0.5CH3OH (3-S), [Mn(R,S-L(3))(N3)] (4). In compound 1, the neutral monocarboxylate zwitterion ligand (L(1)) leads to uniform chains with bis(azide)(carboxylate) bridges. For compounds 2-4, the anionic dicarboxylate zwitterions L(2) and L(3) lead to (azide)bis(carboxylate) bridges, but the overall coordination networks are different. In 2 and 3-S (or 3-R), chains with the (azide)bis(carboxylate) bridges are connected by L(2) and S,S-L(3) (or R,R-L(3)), respectively, to give achiral and chiral 2D coordination networks with different connecting topologies. In compounds 4, which is derived from the mesomeric ligand R,S-L(3), linear trinuclear units with the (azide)bis(carboxylate) bridges are linked by µ-1,3 azides to give 2D layers, and the layers are pillared into a 3D framework by the 1,3-dimethyleneimidazolium tethers. Magnetic analyses suggested that compounds 1-3 behave as 1D antiferromagnetic systems, while 4 shows canted antiferromagnetism with weak ferromagnetic ordering below T(C) = 12.4 K.

Three-dimensional networks based on trinuclear motifs with tricomponent azide-carboxylate-tetrazolate cobridges: synthesis, structure and magnetic properties.

Two 3D coordination polymers of Mn(II) with azide and bifunctional zwitterionic ligands bearing both carboxylate and tetrazolate groups, 1-(carboxylatomethyl)-3-(5-tetrazolato)pyridinium (L(1)) and 1-(carboxylatoethyl)-4-(5-tetrazolato)pyridinium (L(2)), were synthesized, and structurally and magnetically characterized. They are formulated as [Mn(3)(L(1))(2)(N(3))(4)(H(2)O)(2)](n)·4nH(2)O (1) and [Mn(3)(L(2))(2)(N(3))(4)(H(2)O)(3)](n)·3.5nH(2)O (2). In both compounds, octahedral Mn(II) ions are linked by the mixed (µ(2)-EO-N(3))(µ(2)-syn,syn-COO)(µ(2)-N(2),N(3)-CN(4)) (CN(4) = tetrazolate and EO = end-on) triple bridges to give anionic linear trinuclear motifs. The motifs are connected through EE-N(3) (EE = end-to-end) bridges to give layers and chains in 1 and 2, respectively, and the cationic pyridinium spacers serve to interlink the layers or chains into three-dimensional frameworks with the α-Po and CdSO(4)-type topology, respectively. Magnetic studies demonstrated that the magnetic interactions within and between the trinuclear motifs, through the tricomponent and EE-N(3) bridges, respectively, are both antiferromagnetic in both compounds.

Manganese(II) coordination polymers with mixed azide and pyridylbenzoate N-oxide ligands: structures and magnetism.

Two novel Mn(II) coordination polymers with azide and 4-(4-pyridyl)benzoic acid N-oxide (4,4-Hopybz) were synthesized and structurally and magnetically characterized. They are formulated as {[Mn(2)(4,4-opybz)(2)(N(3))(2)(H(2)O)(2)]·H(2)O}(n) (1) and {[Mn(4)(4,4-opybz)(5)(N(3))(H(2)O)(8)](N(3))(2)·2H(2)O}(n) (2). Compound 1 contains 2D coordination layers in which the infinite Mn(II) chains with alternating (µ-EO-N(3))(2)(µ-COO) (EO = end-on) and (µ-COO)(µ-O) bridges are interlinked by the backbones of the organic ligands. Compound 2 is a 3D metal-organic framework in which the unique linear tetranuclear clusters with (µ-EO-N(3))(µ-COO) and (µ-COO)(µ-O) bridges are cross-linked by organic backbones, and it represents a new example of the rare 8-connected self-catenated 3D net with the point symbol 4(16)·6(12). Magnetic analyses on the compounds have been performed in the classical-spin approximation, revealing that all the above-mentioned mixed bridging motifs induce weak antiferromagnetic interactions between Mn(II) ions.

Synthesis, structures, and magnetic properties of four copper compounds with 2,2'-dinitrobiphenyl-4,4'-dicarboxylate.

Four copper(II) coordination polymers of 2,2'-dinitrobiphenyl-4,4'-dicarboxylic acid (H(2)dnbpdc), with or without 4,4'-bipyridyl (bipy) as co-ligand, were synthesized under hydrothermal conditions and characterized crystallographically and magnetically. They are formulated as [Cu(2)(dnbpdc)(OH)(2)](n) (1), [Cu(Hdnbpdc)(2)(bipy)](n)·2nH(2)O (2), [Cu(2)(dnbpdc)(2)(bipy)(H(2)O)(2)](n)·2nH(2)O (3) and [Cu(3)(dnbpdc)(2)(bipy)(OH)(2)(H(2)O)](n)·nH(2)O (4). Compound 1 exhibits a 2D coordination network, in which infinite [Cu(µ-OH)(µ-COO)](n) chains are linked by the backbones of the dnbpdc(2-) ligands. Magnetic studies indicated antiferromagnetic coupling through the mixed hydroxo and carboxylate bridges between Cu(II) ions. In 2, mononuclear Cu(II) centers are linked by Hdnbpdc(-) and bipy ligands into 2D grid-like layers. Compound 3 also consists of 2D grid-like coordination layers, which however are based on aqua-bridged Cu(2)(µ-OH(2))(2) units. Magnetic studies showed that the magnetic coupling through the double aqua bridges is antiferromagnetic. Compound 4 exhibits a 3D framework in which [Cu(OH)(COO)](n) chains are linked by bipy and dnbpdc(2-) ligands. The chain has a complicated bridging network involving µ(3)-OH, µ(2)-OH and µ-COO, and magnetic studies revealed overall antiferromagnetic interactions within the chain.