A linear triple-helical supramolecule Ni₉L₆ has been prepared through a controllable self-assembly approach using 1,3-bis-(3-oxo-3-phenylpropionyl)-2-hydroxy-5-methylbenzene (H₃L) and Ni(OAc)₂ under solvothermal conditions. Single-crystal X-ray diffraction analysis confirms the axial C₃ symmetrical helical structure of the product and the temperature-dependent magnetic susceptibility corresponds to a typical shape of a paramagnet showing dominant ferromagnetic exchange couplings between the neighboring Ni^II ions.

Two pairs of enantiomeric compounds with formulas (S)- or (R)-Co₃(ppap)₂(4,4′-bpy)₂(H₂O)₂⋅4 H₂O [(S)-1 or (R)-1], (S)- or (R)-Co₃(ppap)₂(4,4′-bpy)₂(H₂O)₂⋅3 H₂O [(S)- or (R)-2), and related racemic compound Co₃(ppap)₂(4,4′-bpy)₂(H₂O)₂⋅4 H₂O (rac-3; 4,4′-bpy=4,4′-bipyridine, H₃ppap=3-phenyl-2-[(phosphonomethyl)amino]propanoic acid) are reported. Compounds 1 and rac-3 show identical three-dimensional framework structures, whereas compounds 2 have two-dimensional layer structures. Compounds 1 and 2 are catenation isomers, formation of which is controlled solely by the pH of the reaction mixtures, whereas the formation of isomeric compounds 1 and rac-3 is controlled purely by the chirality of the phosphonate ligand. The magnetic properties of fully dehydrated (S)-1, (S)-2, and rac-3 are highly dependent on both structure and chirality.

This paper reports two metal phosphonate clusters containing Mn^III–Schiff base units, namely, [Mn₂(5-Brsalen)₂(C₁₀H₇PO₃H)₂]·2CH₃OH (1) and [Mn₆(5-Brsalen)₆(C₁₀H₇PO₃)₂(H₂O)₂](ClO₄)₂·7.6H₂O (2) [5-Brsalen = N,N′-ethylenebis(5-bromosalicylideneiminate) dianion]. Compound 1 shows a discrete dinuclear structure in which dimers of Mn₂(5-Brsalen)₂ are terminated by the naphthylphosphonate ligand. In 2, each naphthylphosphonate ligand connects three Mn atoms, forming triangular units of {Mn₃PO₃}, which are further cross-linked through phenoxide oxygen atoms into a hexanuclear cluster. Magnetic studies reveal that the exchange couplings mediated through the phenoxide bridges within the dimer are ferromagnetic in compounds 1 and 2. Further, slow magnetization relaxation, characteristic of single-molecule magnets (SMMs), is observed in both 1 and 2, in contrast to the non-SMM behavior in the precursor of [Mn(5-Brsalen)(H₂O)]₂(ClO₄)₂.

Two pairs of enantiomeric Co^II compounds with formulas [Co₂(μ₃-OH)(cyamp)(C_nH_2n+1COO)] (cyampH₂=(S)- or (R)-[(1-cyclohexylethyl)amino]methylphosphonic acid; n=1 (1); n=7 (2)) were synthesized. The structures of S-1 and S-2 were determined by single-crystal structural analyses. Both crystallize in a monoclinic chiral space group P2₁, and exhibit layered structures in which the Δ-type chains of corner-sharing Co₃(μ₃-OH) triangles are connected by the phosphonate groups. The interlayer spaces are filled with the organic groups of the phosphonate and carboxylate ligands. Therefore, the distances between the layers can be manipulated by the length of the alkyl chain of the carboxylate ligands, from 14.6 Å in 1 to 20.0 Å in 2. Magnetic studies were carried out for compounds S-1 and S-2. Both show metamagnetism at low temperature. The critical field decreases with increasing interlayer distance from 8.18 kOe for S-1 to 7.01 kOe for S-2 at 1.8 K. The optical properties were also studied.

Two cobalt phosphonates, [Co₂(2,2′-bpy)₂(H₂O)(pbtcH)] (1) and [Co₂(H₂O)(pbtcH)(phen)₂] (2; pbtcH₅=5-phosphonatophenyl-1,2,4-tricarboxylic acid, 2,2′-bpy=2,2′-bipyridine, phen=1,10-phenanthroline), with layer structures are reported. Compound 1 contains O-C-O and O-P-O bridged tetramers of Co₄, which are further connected by pbtcH⁴⁻ units to form a layer. In compound 2, the cobalt tetramers made up of water-bridged Co₂ dimers and O-P-O linkages are connected into a layer by pbtcH⁴⁻ units. Upon dehydration, compounds 1 and 2 experience single-crystal-to-single-crystal (SC–SC) structural transformations to form [Co₂(2,2′-bpy)₂(pbtcH)] (1 a) and [Co₂(pbtcH)(phen)₂] (2 a), respectively. The process is reversible in each case. Notably, a breathing effect is observed for 1, accompanied by pore opening and closing due to the reorientation of the coordinated 2,2′-bpy molecules. The transformation was also monitored by in situ IR measurements. Magnetic studies reveal that antiferromagnetic interactions are mediated between the magnetic centers in compounds 1 and 1 a, whereas ferromagnetic interactions are dominant in compound 2.

A new dysprosium(III) phosphonate dimer {Dy(notpH₄)(NO₃)(H₂O)}₂⋅8 H₂O (1) [notpH₆=1,4,7-triazacyclononane-1,4,7-triyl-tris(methylenephosphonic acid)] that contains two equivalent Dy^III ions with a three-capped trigonal prism environment is reported. Complex 1 can be transformed into {Dy(notpH₄)(NO₃)(H₂O)}₂ (2) in a reversible manner by desorption and absorption of solvent water at ambient temperature. This process is accompanied by a large dielectric response. Magnetic studies reveal that both 1 and 2 show thermally activated magnetization relaxation as expected for single-molecule magnets. Moreover, the magnetic dynamics of the two compounds can be manipulated by controlling the number of solvent molecules at room temperature.

The reaction of 1-phosphonomethyl-2-benzimidazolpyrrolidine (pmbpH₂) and CuCl₂ under slightly different conditions has generated three isomers: [Cu(pmbp)]⋅2.5 H₂O (1), [Cu(pmbp)]⋅2 H₂O (2), and [Cu(pmbp)(H₂O)]⋅x H₂O (3). All show 1D chain structures in which the adjacent Cu^II ions are connected purely by the OPO bridges, but the chains are packed in different manners. Dominant antiferromagnetic interactions are observed in these compounds. However, the coupling constant between the metal centers varies significantly for the isomers, which is attributed mainly to the intrachain structural parameters, such as the intrachain Cu⋅⋅⋅Cu distance and the torsion angles over the phosphonate bridge. DFT calculations have been conducted to understand the magnetostructural relationship.

A new layered metal–organic hybrid compound, namely, [Co₃(μ₃-OH)₂(BTP)₂] (1; BTP=4-(3-bromothienyl)phosphonate), is reported. The inorganic layer can be viewed as a pseudo-Kagomé lattice composed of corner-sharing irregular triangles of Co₃(μ₃-OH), with the cavities filled with the PO₃ groups. The interlayer space is occupied by the 3-bromothienyl groups of BTP²⁻. The bulk sample of compound 1 experiences a long-range ferromagnetic ordering below 30.5 K, with a coercivity (H_c) of 5.04 kOe at 5 K. A systematic study on the size-dependent magnetic coercivity of 1 reveals that the coercivity of 1 increases with reduced particle size from the micrometer to the nanometer scale. When the particle size is about 50–200 nm, the coercivity reaches 24.2 kOe at 5 K. The results demonstrate that compound 1 can vary from a soft magnet to one of the hardest molecule-based magnets, simply by reducing the particle size to nanoscale region.

The first examples of metal phosphonates based on 6-phosphononicotinic acid (pnaH₃), namely, M₃(pna)₂(H₂O)₂ {1: M = Cu^II, 2: M = Co^II} are reported. Both possess pillared layered structures. Within the inorganic layer, chains made up of dimers of edge-sharing {M2O₆} octahedra and {M1O₆} octahedra through O(1W), O–P–O, and O–C–O units are interconnected by {PO₃C} tetrahedra. The pyridyl groups of pna^3– serve as the pillars. An antiferromagnetic ground state is found for each compound. When the external field reaches critical points at low temperature, compound 1 features a spin flop transition, whereas 2 shows metamagnetic behavior.

Phosphonic acid (PO₃H₂) terminated self-assembled monolayers (SAMs) on a gold surface were used as a functional interface to immobilize hemoglobin (Hb). In situ surface-enhanced infrared absorption spectroscopy (SEIRAS) measurements show that Hb immobilization is a sluggish process due to formation of multilayer Hb structures on the PO₃H₂-terminated SAMs, as revealed by ellipsometry, atomic force microscopy (AFM), and cyclic voltammetry (CV). In the multilayered Hb film, the innermost Hb molecules can directly exchange electrons with the electrode, whereas Hb beyond this layer communicates electronically with the electrode via protein–protein electron exchange. In addition, electrochemical measurements indicate that immobilization of Hb on the PO₃H₂-terminated SAMs is not driven by the electrostatic interaction, but likely by hydrogen-bonding interaction. The immobilized Hb molecules show excellent bioelectrocatalytic activity towards hydrogen peroxide, that is, the PO₃H₂-terminated SAMs are promising for construction of third-generation biosensors.