Change In Coordination Number Research Articles

Amorphous GaN: Polyamorphism and crystallization at high pressure

Employing constant pressure ab initio simulations, we have shed light on the previously unknown high-pressure behavior of amorphous gallium nitride. Our findings reveal a two-step transformation sequence under pressure. The initial transition involves a polyamorphic transformation from a low-density amorphous (LDA) phase to a high-density amorphous (HDA) phase with an average coordination number of 5.4. Upon pressure release, the HDA state partially reverts to a denser amorphous network with a higher coordination number (4.34) compared to the original LDA phase. Further pressurization triggers the crystallization of the HDA state into a rocksalt structure. Remarkably, the electronic structure of the amorphous forms of GaN exhibits insignificant sensitivity to changes in coordination number, maintaining a band gap of approximately 1.7–2.0 eV across all phases.

Thermal Expansion of Metal Oxides in Silicate Melts: A Simple Theoretical Analysis

The isobaric, isochemical coefficient of thermal expansion ( α) is the proportionality constant relating ∂V/V and ∂T. Noting that ∂V/V equals ∂lnV at constant pressure and composition (i.e., P and X): α=(∂VV∂T)P,X=(∂lnV∂T)P,X A polynomial expression for the temperature dependence of lnV yields direct and accurate calculation of α of melts and glasses. Using the approach, αG of Na-silicate glasses is shown to be constant between 300 and ∼650 K (P and X constant), but it increases linearly with Na2O content, indicating that α is controlled mostly by Na behaviour. Values of α for a melt or glass are necessarily (thermodynamically) related to the coefficients of thermal expansion of its ‘N’ melt components ( αN) by: α=α1θ1+α2θ2+α3θ3+⋯+αNθN where θ represents volume fraction of a component. Calculated αNa2O and αSiO2 values compare satisfactorily with reported values for melts containing ∼40–60 mole% Na2O but are less satisfactory for highly siliceous melts, implying need for refinement of α values. The Coulombic force of attraction between cation and anion is the primary determinant of the magnitude of α values of alkali and alkaline earths oxides. Their values represent a lower bound on α of 3d and 4f modifier oxides. Values larger than this lower bound likely result from a change in coordination number (CN) from higher to lower CN values of modifier cations. Experimental and molecular dynamics studies indicate that partial charges on NBO (O of Si-O-M moieties) and BO (O of Si-O-Si moieties) are about −0.96 and −0.64 respectively, thus NBOs should be incorporated into the first coordination spheres of modifier cations in preference to BOs. A simple mechanism is proposed whereby NBO-BO exchange occurs and CN of the modifier cation decreases with minimal topological adjustment or energetic cost to the melt.

Enhanced Carbon-Carbon Coupling at Interfaces with Abrupt Coordination Number Changes.

Cu-catalyzed electrochemical CO2 reduction reaction (CO2RR) produces multi-carbon (C2+) chemicals with considerable selectivities and activities, yet required high overpotentials impede its practical application. Here, we design interfaces with abrupt coordination number (CN) changes that greatly reduce the applied potential for achieving high C2+ Faradaic efficiency (FE). Encouraged by the mechanistic finding that the coupling between *CO and *CO(H) is the most probable C-C bond formation path, we use Cu2O- and Cu-phthalocyanine-derived Cu (OD-Cu and PD-Cu) to build the interface. Using operando X-ray absorption spectroscopy (XAS), we find that the Cu CN of OD-Cu is ~11, favoring CO* adsorption, while the PD-Cu has a COH*-favorable CN of ~4. Operando Raman spectroscopy revealed that the interfaces with abrupt CN changes promote *OCCOH formation. As a result, the designed catalyst achieves a C2+ FE of 85±2 % at 220 mA cm-2 in a zero-gap CO2 electrolyzer. An improvement of C2+ FE by 3 times is confirmed at the low potential regime where the current density is 60-140 mA cm-2, compared to bare OD-Cu. We report a 45-h stable CO2RR operation at 220 mA cm-2, producing a C2+ product FE of ~80 %.

Structural Aspects of Ambient-Temperature Densification of Highly Crack-Resistant Borosilicate and Aluminoborosilicate Glasses: Two Case Studies Examined by Solid-State NMR.

The structural aspects of ambient-temperature densification via pressurization at 25 GPa were studied by solid-state NMR for two case studies: An alkaline earth boroaluminosilicate glass with the composition 6CaO-3SrO-1BaO-10Al2O3-10B2O3-70SiO2 (labeled SAB) and a sodium magnesium borosilicate glass with the composition 10Na2O-10MgO-20B2O3-60SiO2 (labeled MNBS). For SAB glass, cold pressurization results in significant increases in the average coordination numbers of both boron and aluminum, in line with previous results found in hot-compressed alkali aluminoborosilicate glasses. In addition, 27Al/11B dipolar recoupling experiments reveal a significant decrease in the 11B/27Al dipolar interaction strength upon pressurization, suggesting that the higher-coordinated boron and aluminum species experience weaker magnetic interactions. While this is an expected consequence of the longer internuclear distances involving higher coordination states, the magnitude of the effect also is consistent with a decrease of average B-O-Al internuclear connectivity. By conjecture, a decreased B-O-Al connectivity may present a mechanism of plastic flow inhibiting crack initiation in aluminoborosilicate glasses. In the case of the MNBS glass, no change in the average boron coordination number was observed within experimental error; however, densification increases the extent of B-O-Si connectivity at the expense of small ring structures with dominant B-O-B connectivity. With regard to boron coordination, the data obtained for both case studies differ from those previously found in a series of alkali borosilicate glasses, which had shown an unexpected decrease in N4 upon increased pressure. The results of the present study highlight the importance of changes of medium-range order regarding densification.

Selectivities of Cu edges surface environment for C1 and C2 pathways

Copper (Cu) is an effective catalytic material for the electrochemical CO2 reduction reaction (CO2RR). The final products are highly reliant on surface conditions, and edge models can effectively expose different surface environments, which provide a large number of representative adsorption sites. Compared with the traditional Cu(111), the change of coordination number (CN) and the formation of OCu bond greatly increase the number of electrons transferred during CO2 activation. First-principles calculations have found that the adsorption site at the outer edge (6-site) of the step surface exhibits a significant advantage in both the C1 and C2 pathways. Due to its minimum CN, there is deep p-d hybridization, resulting in the lower Gibbs free energy (G) at the rate-determining steps (RDS). Specifically, the overpotentials are only 0.74 and 0.66 V during C1 and C2 pathways, respectively, indicating good catalytic performance. Differences in surface conditions will inevitably induce better adsorption state of intermediates, optimizing the selectivity of CO2RR. Our current work potentially provides a new avenue for designing more efficient and selective Cu electrocatalysts.

Pressure-induced phase transitions of intermetallic TMBe2 (TM = Zr and Hf) from first-principles calculations

High-pressure stable structures of intermetallic TMBe2 (TM = Zr and Hf) have been fully explored up to 40 GPa using particle swarm structure searches combined with first-principles calculations. The resulting findings show that both intermetallics undergo a structure transition from the ambient-pressure layered AlB2-type structure to a uniform orthorhombic Cmcm structure at 4.5 GPa and 13.8 GPa, respectively. The significant volume collapses under high pressure indicate that the structural transitions of two intermetallics are typical first-order. During the pressure-induced phase transition process, the formation of newly folded Be hexagonal rings in the high-pressure Cmcm structure with unusual change of coordination numbers of TM atoms was attributed to the alternating distortions of the layer-like Be hexagonal rings in ambient AlB2-type structure. The contributions of atomic orbitals near the Fermi level changes correspondingly before and after the structural phase transition, demonstrated by an analyses of electronic band structures and density of states. An obvious degeneracy of TM-d orbitals in the new high-pressure Cmcm structure was further revealed. Additionally, a systematic comparative analysis of mechanical parameters and anisotropic distributions of TMBe2 intermetallics with two structures was performed.

Liquid-Liquid Crossover in Water Model: Local Structure vs Kinetics of Hydrogen Bonds.

In equilibrium and supercooled liquids, polymorphism is manifested by thermodynamic regions defined in the phase diagram, which are predominantly of different short- and medium-range order (local structure). It is found that on the phase diagram of the water model, the thermodynamic region corresponding to the equilibrium liquid phase is divided by a line of the smooth liquid-liquid crossover. In the case of the water model TIP4P/2005, this crossover is revealed by various local order parameters and corresponds to pressures on the order of 3150 ± 350 atm at ambient temperature. In the vicinity of the crossover, the dynamics of water molecules change significantly, which is reflected, in particular, in the fact that the self-diffusion coefficient reaches its maximum values. In addition, changes in the structure also manifest themselves in changes in the kinetics of hydrogen bonding, which are captured by values of such quantities as the average lifetime of hydrogen bonding, the average lifetimes of different local coordination numbers, and the frequencies of changes in different local coordination numbers. An interpretation of the hydrogen bond kinetics in terms of the free energy landscape concept in the space of possible coordination numbers is proposed.

Gallium isotope fractionation during precipitation of α-GaOOH from aqueous solution

Gallium (Ga) has two naturally-occurring stable isotopes: 69Ga (60.1%) and 71Ga (39.9%). Their isotopic ratios were employed as a potential proxy to trace the geochemical behavior of Ga and its analogue Al. Ga is also an important component of many semiconductors. When exposed to aqueous solutions, it may be dissolved and then precipitate as Ga-bearing crystals (e.g., GaOOH). Thus, the exploration of Ga isotope fractionation during α-GaOOH precipitation could be helpful for understanding geochemical behaviors of Ga and other metals (including Al and Fe) during oxyhydroxide precipitation. In this study, three series of precipitation experiments with variable initial aqueous Ga concentrations (about 9.2, 2.0, and 1.8 ppm) were carried out to determine Ga isotope fractionation factor during α-GaOOH precipitation at ∼20 °C and neutral pH as a function of time. The experimental results could be modeled using a Rayleigh precipitation process, in which fractionation factors between crystals and solution (Δ71Gasolid-solution) are between −0.28 and − 0.37‰, depending on the initial Ga concentration and type of matrix anion (Cl− vs. NO3−). This isotope fractionation is significantly smaller in magnitude than the values reported for Ga adsorption on goethite (−0.89‰) and calcite (−1.27‰). The isotope fractionation is mainly caused by the increase in GaO bond length from ∼1.84 Å in aqueous GaOH4— to ∼1.991 Å in α-GaOOH solid, with a simultaneous change of Ga coordination number from 4 to 6, although kinetic isotope fractionation may play an important role. Our study provides the first experimental evidence of significant Ga isotope fractionation during kinetic oxyhydroxide precipitation, and suggests that the measurable Ga isotope fractionation occurred at water-solid interface and during precipitations can be potentially used for tracing global geochemical cycling of Ga and its analogue Al and Fe.

Ultrahigh pressure phase stability of AlB2-type and CaC2-type structures with respect to Fe2P-type and Ni2In-type structures of zirconia

Using density-functional theory, we have performed first-principles calculations to test the phase stability of the hexagonal AlB2-type and tetragonal CaC2-type phases at ultrahigh pressures with respect to the experimentally observed hexagonal Fe2P-type phase and the recently predicted (as post-Fe2P) hexagonal Ni2In-type phase of ZrO2. The phase relations among the four phases have been thoroughly investigated to better understand the high-pressure behavior of ZrO2, especially the upper part of the pressure phase transition sequence. Our enthalpy calculations revealed that the transformation from Ni2In phase to either AlB2 phase or CaC2 phase is unlikely to happen. On the other hand, a direct phase transition from Fe2P phase to Ni2In, CaC2 and AlB2 phases is predicted to occur at 325 GPa, 505 GPa and 1093 GPa, respectively. A deep discussion has been made on the Fe2P → Ni2In and Fe2P → CaC2 transitions in terms of the volume change, the coordination number (CN) change, and the band gap change to obtain a better prediction of the favored post-Fe2P phase of ZrO2. Additionally, the equation of state (EOS) parameters for each phase have been computed using Birch-Murnaghan EOS. To further investigate the phase stability testing, we have studied the components of the enthalpy difference to explore their effect on our findings, and found that all predicted transitions from Fe2P phase are driven by the volume reduction effect when compared to the slight effect of the electronic energy gain.

Joint analysis of macroscopic response and microfabric evolution of coral sand during earthquake-induced liquefaction

This study addresses the microfabric evolution of coral sand during earthquake-induced liquefaction using the joint tests of macroscopic shaking table and microscopic X-ray computed tomography. Based on the non-destructive scanning and image reconstruction in three-dimensional, the change in the grain–pore structure of sands under earthquakes is discussed. Furthermore, the special microstructural evolution of coral sand is studied by the contrast tests with Fujian sand. The results show that the coordination number of coral sand is larger than that of Fujian sand after liquefaction, which is consistent with that the reduction in acceleration of coral sand is smaller than that of the Fujian sand, and the coral sand foundation still has a larger shear strength due to the smaller excess pore pressure accumulation. Moreover, the contact index of Fujian sand and Reigate sand fluctuates in a similar range with the change of void ratio and coordination number compared with coral sand. This is due to the fact that the Fujian sand and Reigate sand are both general terrigenous sands (quartz sand), while coral sand has irregular particle shapes and larger surface friction caused by marine biogenesis. The test results deepen the understanding of the liquefaction mechanism of coral sand.

Effects of Particle Shape and Packing Density on the Mechanical Performance of Recycled Aggregates for Construction Purposes

This paper employs the discrete element method (DEM) to study the mechanical properties of artificial crushed stone. Different grain shapes and gradations are considered, and three types of 3D artificial stone models are generated based on the statistical conclusions in the relevant literature and the observed data. Concurrently, the 3D models of the artificial stones are divided into three groups by their shape parameters (elongation index and flatness index). Furthermore, three types of gradation with different Cu (coefficient of uniformity) and Cc (coefficient of curvature) are also considered. Then, several 3D triaxial compression tests are conducted with the numerical methods to determine the relationship between the grain shapes and their mechanical characteristics. The test results showed that there was a positive correlation between a particles’ angularities and the maximum deviatoric stress in the triaxial compression tests when there were obvious distinctions between the particles. In addition, gradations had a conspicuous impact on the stiffness of the sample. The stress–strain curve possessed a larger slope when the coefficient of curvature was bigger. In terms of shear strength, the results in this paper align well with the traditional shear strength envelope which are convincing for the dependability of the methods used in this paper. The radial deformation capacity and volume strain of the specimen during the triaxial compression tests are also examined. It is believed that there were great differences in deformability between different samples. At the mesoscopic level, the change in coordination number is identified as the fundamental reason for the change in volume strain trend.

Dynamic Behavior Analysis of Wax Crystals during Crude Oil Gelation.

The motion behaviors, rheological properties, and mechanical properties of a wax crystal mesoscale force chain network of waxy crude oil during gelation were experimentally studied and simulated by rheo-optic in situ measurement and computational fluid dynamics-discrete element method (CFD-DEM) numerical simulation, respectively. The motion behavior characteristics of wax crystals and the changes in the average coordination number of wax crystal networks were obtained at different temperatures. The study investigates the rule of crude oil rheological deterioration, the increase of wax crystals, and the changes in wax crystal motion behaviors with decreasing temperature. The relationship between the structure of the mesoscale force chain of the wax crystal network and the motion behaviors of the wax crystal and its rheological properties was analyzed. The results show that the average motion velocity of wax crystals or aggregates decreases from 28.48 to 22.56 μm/s when the temperature decreases from wax appearance temperature (48 °C) to 25 °C. The rotation and rolling trend of wax crystals gradually flatten, and the average coordination number increases 4.39 times. The viscosity of waxy crude oil increases from 6.27 to 8369.7 mPa·s, and the average coordination number of wax crystals obtained by CFD-DEM also increases significantly, which confirms the experimental results. We also found that when the system tended to gelation, a complex and stable force chain network was formed between the wax crystals, with a force chain coverage of 87.93% and a significant increase in the pressure drop in the flow field, which is consistent with the variation pattern of the system viscosity. The micro-meso-dynamic behavior analysis of waxy crude oil combined with CFD-DEM coupling provides a new way to explore the rheological properties of waxy crude oil and the microscopic mechanism of its modification.

Ultrahigh‐Pressure Acoustic Velocities of Aluminous Silicate Glass up to 155 GPa With Implications for the Structure and Dynamics of the Deep Terrestrial Magma Ocean

AbstractWe have carried out in situ high‐pressure acoustic velocity measurements of (Fe2+, Al)‐bearing MgSiO3 glass up to pressures of 155 GPa, which confirmed a distinct pressure‐induced trend change in the transverse acoustic velocity (VS) profile around 98 GPa, likely caused by the Si‐O coordination number (CN) change from 6 to 6+. Although it has been reported that the substitution of Fe2+ in MgSiO3 glass induces almost linear velocity reduction up to ∼160 GPa, we revealed that the VS profile of (Fe2+, Al)‐bearing MgSiO3 becomes anomalously steeper above ∼100 GPa and eventually came to be equivalent to MgSiO3 glass above ∼125 GPa. This implies the incorporation of Al into Fe‐bearing MgSiO3 glass significantly facilitates making it far elastically stiffer and thus the densification under pressures well within the Earth's lower mantle. Our results indicate the possible presence of stiff and highly dense silicate melts in deep MOs in the rocky terrestrial planets.

Efficient optimization of the Li-ion conductivity of borovanadate glass materials for Li-ion batteries

The lithium-doped borovanadate glasses of high chemical purity are obtained via the traditional-melt quenching method. The obtained glasses are identified as having an amorphous character by XRD. DSC spectra reveal the glassy nature and good thermal stability of the prepared samples. FTIR spectroscopy reveals the structural groups of these glasses. The incorporation of Li+ ions into the glass modifies the boron coordination so that the boron coordination number changes from BO4 to BO3. The structural conversion of BO4 to BO3 boosts the number of NBOs. The increased number of NBOs indicates borate network depolymerization and a more open network structure, which leads to Li+ ions easily transferring in the glass network. This, in turn, optimizes the ionic conductivity of the present glassy system and can be of order 10−4 S.cm−1 at 300 K. This is the highest value of ionic conductivity reached by the borovanadate glasses at 300 K. Accordingly, borovanadate glasses containing lithium could pave the way for the use of glass materials as electrode material for Li-ion batteries.

Micro-CT characterization on pore structure evolution of low-permeability sandstone under acid treatment

Permeability enhancement via acid has drawn broad attention in mining and oil industries to treat low-permeability formations to increase the resource recovery rate. In this study, experiments including static acid permeability enhancement tests, flooding acid permeability enhancement tests, and micro-CT scanning were conducted to investigate the mechanism of permeability enhancement and changes in pore structure during acid treatment. First, the extent of reaction between low-permeability sandstone samples and four different acids was evaluated by static tests. The hydrochloric and formic acids exhibited good performance to dissolve filling minerals during static tests. Second, acid flooding in sandstone cores was carried out under reservoir conditions. After acid flooding, the porosities of sandstone cores were significantly increased and a decrease in pressure difference was observed, demonstrating a permeability increase. The pressure difference of hydrochloric acids was lower than that of formic acids at the end of flooding, and the permeability results indicated that the percentage of permeability increase by hydrochloric acid treatment and formic acid treatment were 283% and 120%, respectively. Third, all samples were scanned by micro-CT before and after acid permeability enhancement tests, and CT images were analyzed to study changes in pores, pore throats, and coordination numbers using Avizo software. The mineral compositions and 2D micromorphology were characterized by SEM-EDS, XRD and ICP. After acid treatment, the number of interconnected pores, pore throats, and their equivalent radii all increased, leading to a higher permeability. The improved permeability was mainly due to the dissolution of dolomite, which was identified by SEM-EDS and ICP.

Tetracarbonates in silicate melts may be at the origin of a deep carbon reservoir in the deep Earth

Much of Earth’s carbon may have been stripped away from the silicate mantle by dense metallic-iron during core formation. However, at deep magma ocean conditions carbon becomes less siderophile and thus large amounts of it may be stranded instead in the deep mantle. Here, we describe the structure and compaction mechanisms of carbonate glass to deep mantle pressures. Our results, based on non-resonant inelastic X-ray scattering, X-ray diffraction and ab initio calculations, demonstrate a pressure-induced change in hybridization of carbon from sp2 to sp3 starting at 40 GPa, due to the conversion of [3]CO32- groups into [4]CO44- units, which is completed at ~112 GPa. The pressure-induced change of carbon coordination number from three to four increases possibilities for carbon-oxygen interactions with lower mantle silicate melts. sp3 hybridized carbon provides a mechanism for changing the presumed siderophile nature of deep carbon, becoming a possible source for carbon-rich emissions registered at the surface in intra-plate and near-ridge hot spots.

Reactions of Nickel Ions in Water Radiolysis up to 300 °C

Radiation chemistry of hydrated metal ions plays a significant role in the field of nuclear energy, especially regarding water radiolysis in coolant water in nuclear reactors. This work reports new experimental data on the reactivity of Ni2+/+ species under critical conditions of temperature and pressure. The reaction rates of hydrated nickel ions with water radiolysis products (e-aq, •OH, H, and H2O2) have been investigated for a 25-300 °C temperature range and 200 bar pressure using electron pulse radiolysis/transient absorption. Extensive experiments with the Ni2+/+ species in various salts and pH up to 300 °C were performed. Kinetic decay traces of short-lived monovalent nickel ions were fitted to extract the rate constants versus temperature up to 300 °C. A blue shift of the absorption spectrum of the monovalent nickel ion with increasing temperature was demonstrated, which may indicate a change in the average coordination number. The Arrhenius parameters for the reactions of Ni2+ with e-aq and Ni+ with •OH, H, and H2O2 were obtained. All measured rate constants increased with temperature and followed Arrhenius behavior.

New insights into the heat capacity enhancement of nano-SiO2 doped alkali metal chloride molten salt for thermal energy storage: A molecular dynamics study

Molten salts and their based nanofluids are important media for heat transfer and thermal energy storage in concentrated solar power (CSP) system. To improve the overall efficiency of the CSP plants, it is important to increase the specific heat capacity of molten salt to the extent possible. Nanomaterials have been doped in molten salt to enhance the specific heat capacity of molten salt; however, the mechanism of enhancement in specific heat capacity caused by doping of nanoparticles in molten salt is still unclear. In this work, the Buckingham force field parameters for alkali metal chloride molten salts (KCl, NaCl, LiCl) were first derived and carefully validated. The specific heat capacities, viscosities, and self-diffusion coefficients of pure molten salts and the specific heat capacities of molten-salt-based nanofluids with SiO2 nanoparticles were investigated by molecular dynamics (MD) simulations. The calculated thermophysical properties of the chloride molten salts using the derived Buckingham potential parameters are in good agreement with the experimental data, and the overall prediction performance is better than that of the BMH potential. Results show that the specific heat capacity of molten salt first increases and then decreases with increasing SiO2 doping ratio, reaching a maximum value at 1 wt%. The specific heat capacities of KCl, NaCl and LiCl nanofluids with 1 wt% SiO2 nanoparticle are increased by 6.2 %, 8.6 % and 19.8 % compared to the base salts, respectively. Number density, radial distribution function, coordination number curves, and energy of the nanofluid system were systematically analyzed. It is found that the increase of the specific heat capacities of the molten salt-based nanofluids can be explained by the energy and coordination number change caused by the number density mismatch of cations and anions. Interestingly, the local delamination of cations around SiO2 nanoparticle surfaces in LiCl-SiO2 nanofluids is clearly observed and visualized for the first time; it is a phenomenon well explained by the analysis of number density and contributes to the further enhancement of the heat capacity. The findings of this work could provide important fundamentals in understanding and designing more efficient molten salt nanocomposites for thermal energy storage in future studies.

Magnetic Switchability via Thermal-Induced Structural Phase Transitions in Molecular Solids

Magnetically switchable molecular solids with stimuli-responsive ON/OFF characteristics are promising candidates for smart switches and magnetic storage. In addition to conventional spin-crossover/charge-transfer materials whose magnetic responses arise from changes in the electronic structure of the metal centers, peripheral chemical entities that exhibit tunability provide an alternative and promising tactic for the construction of magnetic multi-stable materials. Temperature changes can trigger a reversible structural phase transition that can affect the coordination environment of a transition-metal center because of the thermal-induced motion of ligands, counterions, neutral guests, and/or changes in coordination number, thus potentially realizing magnetic bistability which can arise from a concomitant spin state change or the modulation of orbital angular momentum. Perspectives and challenges are also highlighted to provide insights into its development.

Tuning the Coordination Geometry and SMM Behavior of Binuclear {LnIII2} Complexes (Ln = Dy, Er) by Varying the Ligand Substitutions

Two series of lanthanide metal complexes [Ln2(H2TEA)2(p-NH2C6H4COO)2(NO3)2] (Ln = Dy (1), Er (2)) and [Ln2(H2TEA)2(p-NO2C6H4COO)4] (Ln = Dy (3), Er (4)) have been synthesized and characterized. Different substituents on benzoate ligands lead to a change in coordination number from nine (for 1 and 2) to eight (for 3 and 4) and a modification of coordination environment, which are further accompanied by a change in SMM behavior. Magnetic susceptibility measurements reveal that for 1 and 2 using p-aminobenzoate as coligand, compound 1 containing DyIII ions displayed single-molecule magnetic (SMM) behavior with the energy barrier Ueff = 98.25 K, while compound 2 containing ErIII ions did not show any sign of slow magnetic relaxation. However, for compounds 3 and 4 using p-nitrobenzoate as coligand, only compound 4 containing ErIII ions exhibits slow relaxation of magnetization expected for a SMM.