Structures,Unimolecular Fragmentations,and Reactivities of the Self‐Assembled Multimetallic/Peptide Complexes [Mnn(GlyGly‐H)2n−1]+ and [Mnn+1(GlyGly‐H)2n]2+

Complexes of Mn²⁺ with deprotonated GlyGly are investigated by sustained off‐resonance irradiation collision‐induced dissociation (SORI‐CID), infrared multiple‐photon dissociation spectroscopy, ion–molecule reactions, and computational methods. Singly [Mn_n(GlyGly‐H)_2n?1]⁺ and doubly [Mn_n+1(GlyGly‐H)_2n]²⁺ charged clusters are formed from aqueous solutions of MnCl₂ and GlyGly by electrospray ionization. The most intense ion produced was the singly charged [M₂(GlyGly‐H)₃]⁺ cluster. Singly charged clusters show extensive fragmentations of small neutral molecules such as water and carbon dioxide as well as dissociation pathways related to the loss of NH₂CHCO and GlyGly. For the doubly charged clusters, however, loss of GlyGly is observed as the main dissociation pathway. Structure elucidation of [Mn₃(GlyGly‐H)₄]²⁺ clusters has also been done by IRMPD spectroscopy as well as DFT calculations. It is shown that the lowest energy structure of the [Mn₃(GlyGly‐H)₄]²⁺ cluster is deprotonated at all carboxylic acid groups and metal ions are coordinated with carbonyl oxygen atoms, and that all amine nitrogen atoms are hydrogen bonded to the amide hydrogen. A comparison of the calculated high‐spin (sextet) and low‐spin (quartet) state structures of [Mn₃(GlyGly‐H)₄]²⁺ is provided. IRMPD spectroscopic results are in agreement with the lowest energy high‐spin structure computed. Also, the gas‐phase reactivity of these complexes towards neutral CO and water was investigated. The parent complexes did not add any water or CO, presumably due to saturation at the metal cation. However, once some of the ligand was removed via CO₂ laser IRMPD, water was seen to add to the complex. These results are consistent with high‐spin Mn²⁺ complexes.     

New insights into water‐soluble and water‐coordinated copper 15‐metallacrown‐5 gadolinium complexes designed for high‐field magnetic resonance imaging applications

The development of contrast agents specifically designed for high‐field magnetic resonance imaging (MRI) is required because the relaxation efficiency of classic Gd(III) contrast agents significantly decreases with increasing magnetic field strengths. With an idea of exploring the unique structure of lanthanide (Ln) 15‐MC‐5 metallacrowns, we developed a series of water‐soluble Gd(III) aqua‐complexes, bearing aminohydroxamate (glycine, α‐alanine, α‐phenylalanine and α‐tyrosine) ligands, with increasing number of water molecules directly coordinated to the Gd(III) ion: Gd(H₂O)₄[15‐MC_Cu(II)Glyha‐5](Cl)₃ ( 1 (Gd)), Gd(H₂O)₄[15‐MC_Cu(II)Alaha‐5](Cl)₃ ( 2 (Gd)), Gd(H₂O)₃[15‐MC_{Cu(II)Phalaha}‐5](Cl)₃ ( 3 (Gd)) and Gd(H₂O)₃[15‐MC_Cu(II)Tyrha‐5](Cl)₃ ( 4 (Gd)). In these systems, the Ln(III) central ion is coordinated by five oxygen donor atoms of the ligands and three or four inner‐sphere water molecules. The X‐ray crystal structure of metallacrown Ln(H₂O)_3,4[15‐MC_Cu(II)Rha‐5]³⁺ agrees with density functional theory predictions. The calculations demonstrate that the exchange of coordinated water molecules can proceed easily, resulting in increased relaxivity parameters. The longitudinal relaxivities (r₁) of 1 (Gd)– 4 (Gd) in water at ultrahigh magnetic field of 9.4 T were determined to be 11.5, 14.8, 13.9 and 12.2 mM^?1 s^?1, respectively. The ability to increase the number of Ln(III) inner‐sphere water molecules up to four, the planar metallacrown structure and the rich hydration shell due to strong hydrogen bonds between the [15‐MC‐5] moiety and bulk water molecules provide new opportunities for potential MRI applications.     

Water‐Soluble Manganese Inorganic Polymers: The Role of Carborane Clusters and Producing Large Structural Adjustments from Minor Molecular Changes

The reaction of two different carboranylcarboxylate ligands, 1‐CH₃‐2‐CO₂H‐1,2‐closo‐C₂B₁₀H₁₀ or 1‐CO₂H‐1,2‐closo‐C₂B₁₀H₁₁, with MnCO₃ in water leads to polymeric compounds 1 a and 1 b . Both compounds have been characterized by analytical and spectroscopic techniques. Additionally, electrochemical techniques have also been used for compound 1 a . X‐ray analysis revealed substantial differences between both compounds: whereas a six‐coordinated Mn^II compound with water molecules bridging two Mn^II centers has been observed for 1 a , a square pyramidal geometry around each Mn^II ion with terminal water molecules coordinated to each Mn^II center has been found for 1 b . The observed differences have been attributed to the existence of different substituents, ?CH₃ or ?H, on one of the carbon atoms of the carboranylcarboxylate ligand. The reaction of 1 a and 1 b with coordinating solvents, such as ethers or Lewis bases, leads to the formation of new compounds with low (mononuclear 4 a , 4 b ; dinuclear 3 a , 3 b ; and trinuclear 2 a ) or high nuclearity (hybrid polymer, 5 a ), due to breakage of the corresponding polymer. X‐ray analysis shows that the structural core present in the polymeric materials is not maintained in the resulting compounds, with the exception of trinuclear compound 2 a . The magnetic properties of the compounds studied show weak antiferromagnetic coupling.     

Superoxide Dismutase Activity of the Naturally Occurring Human Serum Albumin–Copper Complex without Hydroxyl Radical Formation

The superoxide radical anion (O₂^.?) is biologically toxic and contributes to the pathogenesis of various diseases. Here we describe the superoxide dismutase (SOD) activity of human serum albumin (HSA) complexed with a single Cu^II ion at the N‐terminal end (HSA–Cu complex). The structure of this naturally occurring copper‐coordinated blood serum protein has been characterized by several physicochemical measurements. The O₂^.? dismutation ability of the HSA–Cu (1:1) complex is almost the same as that of the well‐known SOD mimics, such as Mn^III‐tetrakis(N‐methylpyridinium)porphyrin. Interestingly, the HSA–Cu complex does not induce a subsequent Fenton reaction to produce the hydroxyl radical (OH^.), which is one of the most harmful reactive oxygen species.     

General Protocol for the Synthesis of Functionalized Magnetic Nanoparticles for Magnetic Resonance Imaging from Protected Metal–Organic Precursors

The development of magnetic nanoparticles (MNPs) with functional groups has been intensively pursued in recent years. Herein, a simple, versatile, and cost‐effective strategy to synthesize water‐soluble and amino‐functionalized MNPs, based on the thermal decomposition of phthalimide‐protected metal–organic precursors followed by deprotection, was developed. The resulting amino‐functionalized Fe₃O₄, MnFe₂O₄, and Mn₃O₄ MNPs with particle sizes of about 14.3, 7.5, and 6.6 nm, respectively, had narrow size distributions and good dispersibility in water. These MNPs also exhibited high magnetism and relaxivities of r₂=107.25 mM^?1 s^?1 for Fe₃O₄, r₂=245.75 mM^?1 s^?1 for MnFe₂O₄, and r₁=2.74 mM^?1 s^?1 for Mn₃O₄. The amino‐functionalized MNPs were further conjugated with a fluorescent dye (rhodamine B) and a targeting ligand (folic acid: FA) and used as multifunctional probes. Magnetic resonance imaging and flow‐cytometric studies showed that these probes could specifically target cancer cells overexpressing FA receptors. This new protocol opens a new way for the synthesis and design of water‐soluble and amino‐functionalized MNPs by an easy and versatile route.     

Proton‐Conducting Magnetic Coordination Polymers

Three isostructural lanthanide‐based two‐ dimensional coordination polymers (CPs) {[Ln₂(L)₃(H₂O)₂]_n ? 2n CH₃OH) ? 2n H₂O} (Ln=Gd³⁺ ( 1 ), Tb³⁺ ( 2 ), Dy³⁺ ( 3 ); H₂L=cyclobutane‐1,1‐dicarboxylic acid) were synthesized by using a low molecular weight dicarboxylate ligand and characterized. Single‐crystal structure analysis showed that in complexes 1 – 3 lanthanide centers are connected by μ₃‐bridging cyclobutanedicarboxylate ligands along the c axis to form a rod‐shaped infinite 1D coordination chain, which is further linked with nearby chains by μ₄‐connected cyclobutanedicarboxylate ligands to form 2D CPs in the bc plane. Viewing the packing of the complexes down the b axis reveals that the lattice methanol molecules are located in the interlayer space between the adjacent 2D layers and form H‐bonds with lattice and coordinated water molecules to form 1D chains. Magnetic properties of complexes 1 – 3 were thoroughly investigated. Complex 1 exhibits dominant ferromagnetic interaction between two nearby gadolinium centers and also acts as a cryogenic magnetic refrigerant having a significant magnetic entropy change of ?ΔS_m=32.8 J kg^?1 K^?1 for ΔH=7 T at 4 K (calculated from isothermal magnetization data). Complex 3 shows slow relaxation of magnetization below 10 K. Impedance analysis revealed that the complexes show humidity‐dependent proton conductivity (σ=1.5×10^?5 S cm^?1 for 1 , σ=2.07×10^?4 S cm^?1 for 2 , and σ=1.1×10^?3 S cm^?1 for 3 ) at elevated temperature (>75 °C). They retain the conductivity for up to 10 h at high temperature and high humidity. Furthermore, the proton conductivity results were correlated with the number of water molecules from the water‐vapor adsorption measurements. Water‐vapor adsorption studies showed hysteretic and two‐step water vapor adsorption (182000 μL g^?1 for 1 , 184000 μL g^?1 for 2 , and 1874000 μL g^?1 for 3 ) in the experimental pressure range. Simulation of water‐vapor adsorption by the Monte Carlo method (for 1 ) confirmed the high density of adsorbed water molecules, preferentially in the interlayer space between the 2D layers.     

Designing Novel Contrast Agents for Magnetic Resonance Imaging. Synthesis and Relaxometric Characterization of three Gadolinium(III) Complexes Based on Functionalized Pyridine‐Containing Macrocyclic Ligands

The three novel pyridine‐containing 12‐membered macrocyclic ligands 1 – 3 were synthesized. The coordinating arms are represented by three acetate moieties in 1 and 3 and by one acetate and two phosphonate moieties in 2 . In all three ligands, the acetate arm in the distal position is substituted, with a benzyl group in 1 and 2 and with an arylmethyl moiety in 3 . The relaxivities r_1p (20 MHz, 25°) of Gd^III complexes are: GD?1 , r_1p=8.3 mM ^?1 s^?1; GD?2 , r_1p8.1 mM ^?1 s^?1; Gd?3 , r_1p10.5 mM ^?1 s^?1. ¹H‐NMRD and ¹⁷O‐NMR T₂ data show that Gd?1 and Gd?3 contain two H₂O molecules in the inner sphere, whereas the presence of two phosphonate arms allows the coordination of only one H₂O molecule in Gd?2 . Interestingly, the exchange lifetime of coordinated H₂O in the three complexes is similar in spite of the difference in the coordination number of the Gd^III ion (i.e., 9 in Gd?1 and Gd?3 , and 8 in Gd?2 ). ¹H‐Relaxometric measurements at different pH and in the presence of lactate and oxalate were carried out to get some insight into the formation of ternary complexes from Gd?1 and Gd?3 . Finally, it was found that binding to human‐serum albumin (HSA) of Gd?1 and Gd?2 , though weak, yields limited relaxivity enhancements, likely as a consequence of effects on the hydration sphere caused by donor atoms on the surface of the protein.     

Gadolinium(III) Complexes of dota‐Derived N‐Sulfonylacetamides (H4(dota‐NHSO2R)=10‐{2‐[(R)sulfonylamino]‐2‐oxoethyl}‐1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic Acid): A New Class of Relaxation Agents for Magnetic Resonance Imaging Applications

Four new ligands for lanthanide ions based on the H₃do3a (=1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid) structure and bearing one N‐sulfonylacetamide arm were synthesized, i.e., H₄dota‐NHSO₂R=10‐{2‐[(R)sulfonylamino]‐2‐oxoethyl}‐1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acids 1a – e . A ¹⁵N‐NMR study of the ¹⁵N‐labelled Eu³⁺ complex of one such ligands, 1d , showed that the coordination of the N‐sulfonylacetamide arm involves the carbonyl O‐atom rather than the N‐atom. The relaxometric properties of the corresponding Gd³⁺ complexes were investigated as a function of pH and temperature. These complexes have relaxivities in the range 4.5–5.3 mM ^?1 s^?1, at 20 MHz and 25°, and are characterized by a single H₂O molecule in their inner coordination sphere. The mean residence lifetime of this molecule is relatively long (500–700 ns) compared to other anionic complexes. The slow rate of H₂O exchange can be justified by the extensive delocalization of the negative charge on the N‐sulfonylacetamide arm. The long residence time of the coordinated H₂O allowed the observation of the effect of the prototropic exchange on the relaxivity. The study of the interaction between the complex [Gd( 1e )]‐ and HSA revealed a weak affinity constant highlighting the importance of a localized negative charge on the complex to promote a strong interaction with the protein.     

Amphiphilic Ditopic Bis‐Aqua Gd‐AAZTA‐like Complexes Enhance Relaxivity of Lipidic MRI Nanoprobes

Two amphiphilic mono‐ and dimeric GdAAZTA‐like chelates composed of stable bis‐aquo Gd^III complexes (q=2) linked to one (for the monomer) or two dodecyl aliphatic chains (for the dimer) were synthesized. Both chelates showed high relaxivity when incorporated into the lipid bilayer of liposomes or after interaction with human serum albumin (HSA). The ditopic complex shows a significantly decreased internal motion relative to the monomeric complex, associated with an enhanced relaxivity (r₁≈60 mm ^?1 s^?1, at 30 MHz and 310 K). The presence of two metal‐bound water molecules in fast exchange and the restricted rotational freedom make the relaxivity of this system the highest measured for paramagnetic liposomes.     

MnOx Nanoparticles Supported on a New Mesostructured Silicate with Textural Porosity

A two‐step synthesis of a novel mesostructured silicate, KIL‐2, and its manganese‐containing analogue, Mn/KIL‐2, has been developed. KIL‐2 possesses interparticle mesopores with pore dimensions between 5 and 60 nm and a surface area of 448 m². The mesopores are formed by the aggregation of silica nanoparticles, which creates a network with interparticle voids. The particle size and the pore diameters depend on the temperature of the ageing step (first step) and on the solvothermal treatment in ethanol (second step), respectively. Mn/KIL‐2 contains octahedrally coordinated Mn³⁺ (80 %) and tetrahedrally coordinated Mn²⁺ (20 %) ions. Mn³⁺ ions are present in the extra‐framework MnO_x nanoparticles with typical dimensions of 2 nm, which are homogeneously distributed throughout the material. Mn²⁺ ions occur as isolated manganese framework sites. The material is also able to retain its structure characteristics after the hydrothermal treatment in boiling water. Because of its non‐toxic nature and cost‐effective synthesis, Mn/KIL‐2 thus exhibits properties that are needed for an environment‐friendly catalyst.     

Stability and Dynamics of Cyclic Diguanylic Acid in Solution

Cyclic diguanylic acid (CDG) is a ubiquitous messenger involved in bacterial signaling networks. Despite its central role in motility, biofilm formation, virulence, and flagellum development, fundamental properties such as its aggregation state are still poorly understood. Here the dynamics and stability of metal‐free and Mg²⁺‐bound CDG are characterized. Atomistic simulations establish that the CDG dimer is slightly favored (by ?5 kcal mol^?1) over its dissociated form (2 CDG), while the Mg²⁺ ion coordinated in the X‐ray structure readily dissociates from (CDG)₂ in solution and prefers water coordination. As a ligand in a protein, CDG binds both as a U‐shaped and a quasilinear monomer. The current results indicate that the energy difference between these two conformations is only a few kilocalories per mole, which explains the facile adaptation to different protein environments. This, together with the slight preference of (CDG)₂ over 2 CDG suggests that (CDG)₂ binding to a protein does probably not occur via sequential binding of two individual monomers.     

Surface and Structural Investigation of a MnOx Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions

Catalytically active MnO_x species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnO_x catalysts form without supports in situ under photocatalytic conditions. Our most active ⁴MnO_x catalyst (～0.84 mmol O₂ mol Mn^?1 s^?1) forms from a Mn₄O₄ bearing a metal–organic framework. ⁴MnO_x is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m²g^?1) and small regions of crystallinity and layer flexibility. In contrast, the ^SMnO_x formed from Mn²⁺ salt gives an amorphous species of lower surface area (80 m²g^?1) and lower activity (～0.15 mmol O₂ mol Mn^?1 s^?1). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p_3/2 core levels detects enriched Mn³⁺ and Mn²⁺ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.     

Employing an Unsaturated Th4+ Site in a Porous Thorium–Organic Framework for Kr/Xe Uptake and Separation

Actinide based metal–organic frameworks (MOFs) are unique not only because compared to the transition‐metal and lanthanide systems they are substantially less explored, but also owing to the uniqueness of actinide ions in bonding and coordination. Now a 3D thorium–organic framework ( SCU‐11 ) contains a series of cages with an effective size of ca. 21×24 Å. Th⁴⁺ in SCU‐11 is 10‐coordinate with a bicapped square prism coordination geometry, which has never been documented for any metal cation complexes. The bicapped position is occupied by two coordinated water molecules that can be removed to afford a very unique open Th⁴⁺ site, confirmed by X‐ray diffraction, color change, thermogravimetry, and spectroscopy. The degassed phase ( SCU‐11‐A ) exhibits a Brunauer–Emmett–Teller surface area of 1272 m² g^?1, one of the highest values among reported actinide materials, enabling it to sufficiently retain water vapor, Kr, and Xe with uptake capacities of 234 cm³ g^?1, 0.77 mmol g^?1, 3.17 mmol g^?1, respectively, and a Xe/Kr selectivity of 5.7.     

Using Ho3+ Fluorescence Enhancement as a Novel Probe in Monitoring of Human Serum Albumin

Abstract

In this work, for the first time, the fluorescence enhancement of Ho³⁺ ions is introduced as a novel probe for human serum albumin (HSA) determination in aqueous solution. Lanthanides express very specific luminescence emissions, due to their unfilled 4fⁿ electronic orbital, and thus, the fluorescence of the lanthanide ions can be radically improved when they are coordinated with the appropriate organic molecules. By applying this method, HSA can be determined up to 0.066 mg L^?1.     

Synthesis,Structure, and Magnetic Behavior of a 1‐D Coordination Polymer [Ni(NIT4py)2(ip)(H2O)]n

A new coordination polymer of the formula [Ni(NIT4py)₂(ip)(H₂O)]_n(NIT4py = 2‐(4′‐pyridinyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide and ip = isophthalate dianion) has been synthesized and characterized by elemental analyses, IR spectrum, and single‐crystal X‐ray diffraction. The coordination about each Ni²⁺ ion is a distorted octahedra. Each isophthalate dianion binds two Ni²⁺ ions in monodentate‐bidentate mode, leading to a 1‐D chain. Among the chains, the coordinated water molecules and carboxylato oxygen atoms form hydrogen bonds, generating an infinite 1‐D ladder structure of a double‐chain. The magnetic study shows that the decrease of χ_MT value in the low temperature for the complex is mainly ascribed to the zero‐field splitting of the distorted octahedral Ni²⁺ ions.     

A Gadolinium‐Binding Cyclodecapeptide with a Large High‐Field Relaxivity Involving Second‐Sphere Water

A new cyclodecapeptide incorporating two prolylglycine sequences as β‐turn inducers and bearing four side chains with acidic carboxyl groups for cation complexation has been prepared. Structural analysis in water by ¹H NMR spectroscopy and CD shows that this template adopts a conformation suitable for the complexation of lanthanide ions Ln³⁺, with its carboxyl groups oriented on the same face of the peptide scaffold. Luminescence titrations show that mononuclear Ln–PA complexes are formed with apparent stability constants of log β₁₁₀≈6.5 (pH 7). The high‐field water relaxivity values arising from the Gd–PA complex at 200–500 MHz have been interpreted with molecular parameters determined independently. The experimentally determined water relaxivities are undoubtedly 30 % higher than the expected values for this complex with two inner‐sphere (IS) water molecules and a medium‐range rotational correlation time (τ_R=386 ps (±10 %)). This led us to propose the existence of a large second‐sphere (2S) contribution to the relaxivity caused by the interaction of water molecules with the hydrophilic peptide ligand by hydrogen‐bonding.     

Unprecedented Kinetic Inertness for a Mn2+‐Bispidine Chelate: A Novel Structural Entry for Mn2+‐Based Imaging Agents

The search for more biocompatible alternatives to Gd³⁺‐based MRI agents, and the interest in ⁵²Mn for PET imaging call for ligands that form inert Mn²⁺ chelates. Given the labile nature of Mn²⁺, high inertness is challenging to achieve. The strongly preorganized structure of the 2,4‐pyridyl‐disubstituted bispidol ligand L₁ endows its Mn²⁺ complex with exceptional kinetic inertness. Indeed, MnL₁ did not show any dissociation for 140 days in the presence of 50 equiv. of Zn²⁺ (37 °C, pH 6), while recently reported potential MRI agents MnPyC3A and MnPC2A‐EA have dissociation half‐lives of 0.285 h and 54.4 h under similar conditions. In addition, the relaxivity of MnL₁ (4.28 mm ^?1 s^?1 at 25 °C, 20 MHz) is remarkable for a monohydrated, small Mn²⁺ chelate. In vivo MRI experiments in mice and determination of the tissue Mn content evidence rapid renal clearance of MnL₁. Additionally, L₁ could be radiolabeled with ⁵²Mn and the complex revealed good stability in biological media.     

Field‐Induced Slow Magnetic Relaxation in a Mononuclear Manganese(III)–Porphyrin Complex

We report on a novel manganese(III)–porphyrin complex with the formula [Mn^III(TPP)(3,5‐Me₂pyNO)₂]ClO₄?CH₃CN ( 2 ; 3,5‐Me₂pyNO=3,5‐dimethylpyridine N‐oxide, H₂TPP=5,10,15,20‐tetraphenylporphyrin), in which the Mn^III ion is six‐coordinate with two monodentate 3,5‐Me₂pyNO molecules and a tetradentate TPP ligand to build a tetragonally elongated octahedral geometry. The environment in 2 is responsible for the large and negative axial zero‐field splitting (D=?3.8 cm^?1), low rhombicity (E/|D|=0.04) of the high‐spin Mn^III ion, and, ultimately, for the observation of slow magnetic‐relaxation effects (E_a=15.5 cm^?1 at H=1000 G) in this rare example of a manganese‐based single‐ion magnet (SIM). Structural, magnetic, and electronic characterizations were carried out by means of single‐crystal diffraction studies, variable‐temperature direct‐ and alternating‐current measurements and high‐frequency and ‐field EPR spectroscopic analysis followed by quantum‐chemical calculations. Slow magnetic‐relaxation effects were also observed in the already known analogous compound [Mn^III(TPP)Cl] ( 1 ; E_a=10.5 cm^?1 at H=1000 G). The results obtained for 1 and 2 are compared and discussed herein.     

Switching of the Magnetocaloric Effect of MnII Glycolate by Water Molecules

The transformation of Mn^II glycolates (glc) between the three‐dimensional coordination polymer [Mn(glc)₂]_n ( 1 ) and discrete mononuclear phase [Mn(glc)₂(H₂O)₂] ( 2 ) can be reversibly switched by water molecules, which dramatically change the magnetocaloric effect (MCE) of Mn^II glycolates from the maximum of 6.9 J kg^?1 K^?1 in 1 to 60.3 J kg^?1 K^?1 in 2 . This case example reveals that the effect of magnetic coupling on MCE plays a dominant role over that of other factors such as magnetic density for 3d‐type magnetic refrigerants.