Crystal structure of a heterotrimetallic 12-metalla-crown-4 with 2-propylvalerate anion bridges

The synthesis and single-crystal X-ray structure for tetraaquatetrakis( (cid:2) -2-pro- pylvalerato)tetrakis(

The synthesis and single-crystal X-ray structure for tetraaquatetrakis(-2-propylvalerato)tetrakis( 4 -salicylhydroximato)dysprosiumtetramanganesesodium dimethylformamide tetrasolvate, [DyMn 4 Na(C 7 H4NO 3 ) 4 (C 8 H 15 O 2 ) 4 (H 2 O) 4 ]Á-4C 3 H 7 NO or DyNa(2-PV) 4 [12-MC Mn III Nshi -4](H 2 O) 4 Á4DMF, 1, where MC is metallacrown, shi 3À is salicylhydroximate, 2-PV is 2-propylvalerate, and DMF is N,N-dimethylformamide, is reported. The slightly domed metallamacrocycle contains four ring Mn III ions and four shi 3À ligands that generate an [Mn III -N-O] repeat unit that recurs four times. The ring Mn III ions are fivecoordinate with a square-pyramidal shape. Furthermore, the metallacrown binds both a Dy III ion and a Na + ion in the central cavity. The central ions are located on opposite faces of the cavity with the Dy III ion located on the convex side of the MC and the Na + ion located on the concave side. Each central ion is eight-coordinate although they possess different geometries. The Dy III ion has a square-antiprismatic shape, while the Na + ion has an extremely distorted biaugmented trigonal-prismatic shape. The four 2-propylvalerate anions help to tether the Dy III to the MC cavity by forming bridges between the Dy III ion and each ring Mn III ion. Moreover, the interstitial DMF molecules are hydrogen bonded to the water molecules that complete the coordination environment of the Na + ion. The metallacrown framework (excluding the Dy III and Na + ions), the bridging 2-propylvalerate, and the interstitial DMF molecule experience whole-molecule disorder due to the rotational orientation of the metallamacrocycle. Additionally, the main moiety alkyl chain of the 2propylvalerate is disordered over two additional orientations, and the main moiety interstitial DMF molecule is disordered over one additional orientation. The main moiety of the metallacrown framework refined to 0.9030 (14), while the minor B-moiety refined to 0.0971 (14). The main moiety alkyl chain of the 2-propylvalerate refined to 0.287 (3): 0.309 (3): 0.307 (3), and the minor B-moiety alkyl chain refined to 0.0971 (14). Lastly, the main moiety interstitial DMF refined to 0.549 (3): 0.354 (3), and the minor B-moiety DMF refined to 0.0971 (14).

Chemical context
Materials that combine both 3d and 4f metal ions have potentially interesting magnetic properties as a result of the interaction between the paramagnetic centers. In particular, 3d-4f materials have applications in the areas of single-molecule magnetism (Liu et al., 2015), single-chain magnetism (Wang et al., 2014), and magnetorefrigeration (Lun et al., 2021). The systematic synthesis of these heterometallic compounds is of interest to chemists and material scientists, and metallacrowns (MC) are a class of molecules particularly suited for the investigation of such materials because of their ability to interchange components of the molecule while maintaining the overall structural features (Mezei et al., 2007;Lutter et al., 2018).
Metallacrowns are metallamacrocyclic compounds with a metal-nitrogen-oxygen repeat unit about the inner ring. Several 3d-4f metallacrown systems have proven to be single-molecule magnets (SMM) (Boron, 2022) and magnetorefrigerates (Lutter et al., 2021;Salerno et al., 2021;Saha et al., 2022). Indeed, we have been particularity focused on a lanthanide-manganese 12-metallacrown-4 system, LnNaY 4 [12-MC Mn III Nshi -4], where Y is a carboxylate anion and shi 3À is salicylhydroximate (Azar et al., 2014). These metallacrowns are based on a 12-membered MC ring with four oxygen atoms comprising the MC cavity. In addition, four Mn III are part of the MC ring and the central cavity captures two cations in the central cavity: an Ln III ion and a Na + ion. The two cations bind to opposite sides of the MC cavity. Furthermore, four carboxylate anions bridge between each ring Mn III ions and the central Ln III ion. We first reported these heterotrimetallic compounds with acetate bridges in 2014 (Azar et al., 2014) and demonstrated that the MCs could bind a range of Ln III ions in the central cavity, Pr to Yb (except Pm). Subsequently, we investigated the singlemolecule magnet behavior of a series of DyNaY 4 [12-MC Mn III Nshi -4] compounds, where Y is acetate, trimethylacetate, benzoate, or 2-hydroxybenzoate (i.e. salicylate) (Boron et al., 2016). In this series, only the MCs with bridging 2-hydroxybenzoate anions displayed single-molecule magnet properties. We hypothesized that the Lewis basicity of the bridging ligand may affect the magnetic coupling between the metal centers, thus switching on or off the SMM behavior. The pK a of the parent carboxylic acid was used as a proxy for the Lewis basicity of the carboxylate, with lower pK a values indicating greater electron-withdrawing ability for the subsequent carboxylate anion. For the investigated carboxylate anions, 2-hydroxybenzoic acid has the lowest pK a (2.98) while the other acids are of comparable pK a values, 4.20 for benzoic acid, 4.76 for acetic acid, and 5.03 for trimethylacetic acid (Haynes, 2010). Therefore, 2-hydroxybenzoate is the most electron-withdrawing in the series, and this may affect the magnetic coupling between the Dy III and Mn III ions. We have also extended the types of DyNaY 4 [12-MC Mn III Nshi -4] structures by synthesizing complexes with 3-hydroxy-and 4-hydroxybenzoate (Manickas et al., 2020) and with halogenated benzoate anions (2-fluoro-, 3-fluoro-, 4-fluoro-, 2-chloro-, 3-chloro-, 3-bromo-, and 2-iodobenzoate; (Michael et al., 2021). These carboxylates have a range of pK a values that spans from 2.86 to 4.57 (Haynes, 2010), although at this time we have not investigated the SMM properties of these compounds.
Seeking to expand the types of DyNaY 4 [12-MC Mn III Nshi -4] structures beyond benzoate anions, we decided to determine if 2-propylvalerate, which has two propyl chains off the carboxylate carbon atom, could lead to MC formation. Herein we report the synthesis and crystal structure DyNa(2-PV) 4 [12-MC Mn III Nshi -4](H 2 O) 4 Á4DMF, 1, where 2-PV is 2-propylvalerate and DMF is N,N-dimethylformamide. Although the pK a of the parent 2-propylvaleric acid is 4.6 (Haynes, 2010) and the MC is not expected to possess SMM based on previous results, the 3d-4f compound will allow further investigation into the molecular characteristics that lead to single-molecule magnetism.

Structural commentary
, is centered about a crystallographic C 4 axis along the Dy III and Na + ions located in the central cavity of the metallamacrocycle. The fourfold rotational axis generates a metallacrown with four ring Mn III ions and four shi 3À ligands that yield the Mn III -N-O repeat unit. In addition, four 2-propylvalerate anions form bridges between each ring Mn III ion and the central Dy III ion, and four interstitial DMF molecules are hydrogen bonded to the sodium-coordinated water molecules of the metallacrown. The metallacrown framework (excluding the Dy III and Na + ions), the bridging 2-propylvalerate, and the interstitial DMF molecule experience whole molecule disorder as a result of the rotational orientation of the macrocycle. The main moiety of the molecule has an Mn III -N-O counterclockwise rotation about the C 4 axis, while the minor B-moiety has an Mn III -N-O clockwise rotation about the C 4 axis. Furthermore, the main moiety alkyl chain of the 2-propylvalerate is disordered over two additional orientations, and the main moiety interstitial DMF molecule is disordered over one additional orientation. The main moiety of the metallacrown framework occupancy refined to 0.9030 (14), while the minor B-moiety refined to 0.0971 (14). The main moiety alkyl chain of the 2-propylvalerate occupancies refined to 0.287 (3):0.309 (3):0.307 (3), and the minor B-moiety alkyl chain occupancy refined to 0.0971 (14). Lastly, the main moiety interstitial DMF refined to 0.549 (3):0.354 (3), and the minor B-moiety DMF refined to 0.0971 (14). In the following sections, all numbers refer to the major component, unless stated otherwise. The Refinement section contains complete details of the treatment of the disorder.
The oxidation states of the metal ions were determined based on overall molecular charge considerations, structure features of the manganese ion, and bond-valence sum (BVS) values. The four triply deprotonated shi 3À ligands and four 2-propylvalerate anions provide an overall 16-charge, which is counterbalanced by one Dy III ion, one Na + ion, and four Mn III ions (16+ total charge). In addition, the Mn III ion possesses an elongated bond along the z-axis [2.126 (5) Å ] and compressed bonds in the xy lane [1.840 (4) to 1.946 (5) Å ], which are typical of high spin 3d 4 ions. Lastly, the BVS values (Liu & Thorp, 1993;Trzesowska et al., 2004) indicate that the Dy III and Mn III ions have a 3+ charge (Table 1).
Both central ions, Dy III and Na + , are eight-coordinate although with different coordination geometries ( Fig. 1; Table 2). The metallacrown framework of 1 is slightly domed with the Dy III ion located on the convex side of the metallamacrocycle and the Na + ion located on the concave side. The Dy III ion is bound to the four oxime oxygen atoms of the MC cavity, which are provided by four different shi 3À ligands, and four carboxylate oxygen atoms of four different 2-propylvalerate anions. The carboxylate groups of the 2-propylvalerate anions form three atom bridges to each ring Mn III ion. An analysis of the geometry with the program SHAPE 2.1 (Llunell et al., 2013;Pinsky & Avnir, 1998) best describes the shape as a square antiprism (Casanova et al., 2005). The Continuous Shape Measure (CShM) value is 0.747, indicating that the geometry approaches that of an ideal square antiprism. The Na + ion is also bound to the four oxime oxygen atoms of the MC cavity, and the coordination environment is completed by four water molecules. Each water molecule also hydrogen bonds (Fig. 2) to two interstitial DMF molecules. The geometry of the Na + ion cannot be clearly defined based on CShM values as the two lowest values are 3.667 for a biaugmented trigonal prism and 3.803 for a square antiprism. Typically values above 3.0 indicate significant distortions from ideal geometry; thus, for the Na + ion the geometry cannot be unambiguously specified (Cirera et al., 2005).
The ring Mn III ion is five-coordinate with a square-pyramidal shape (

Figure 2
The single-crystal X-ray structure of DyNa ( the ligand, and the other shi 3À ligand forms a six-membered chelate ring by binding with the oxime nitrogen and phenolate oxygen atom of the ligand. The apical position is occupied by the carboxylate oxygen atom of the bridging 2-propylvalerate anion. Lastly, the water molecule that is coordinated to the Na + ion forms a long interaction [2.527 (5) Å ] with the Mn III ion.

Supramolecular features
For 1, the main metallacrown molecule forms hydrogen bonds to the interstitial DMF molecules via the water molecules bound to the central sodium ion. Each water molecule is hydrogen bonded to the carbonyl oxygen atom of two adjacent DMF molecules (Table 4, Fig. 3). This generates a small hydrogen-bonding network on the concave side of the metallacrown between the four sodium-bound water molecules and the four interstitial DMF molecules. A similar hydrogen-bonding connectivity is also observed for the minor B-moiety of the compound. These hydrogen bonds and pure van der Waals forces contribute to the overall packing of the molecules.  (Azar et al., 2014;Travis et al., 2015Travis et al., , 2016Boron et al., 2016;Cao et al., 2016;Qin et al., 2017;Anthanasopoulou et al., 2018;Manickas et al., 2020;Michael et al., 2021). The central Ln III metal ions include the lanthanide ions from Pr to Yb (except Pm) and yttrium. The counter-cation X is usually an Na + or K + ion that is also bound to the central cavity, but other unbound countercations such as tetrabutylammonium, tetraethylammonium, and triethylammonium have been employed. A range of bridging carboxylate anions (Y) have been used including acetate (OAc), trimethylacetate (TMA), benzoate (ben), 2-hydroxybenzoate (2-OHben), 3-hydroxybenzoate (3-OHben), 4-hydroxylbenzoate (4-OHben), 2-fluorobenzoate (2-Fben), 3-fluorobenzoate (3-Fben), 4-fluorobenzoate (4-Fben), 2-chlorobenzoate (2-Clben), 4-chlorobenzoate (4-Clben), 3-bromobenzoate (3-Brben), and 2-iodobenzoate (2-Iben). Of the forty structures, thirteen contain both Dy III and Na + as in 1 (Azar et al., 2014;Boron et al., 2016;Manickas et al., 2020;Michael et al., 2021). The structural comparison of 1 will be limited to the MCs that contain Dy III and Na + ions captured in the central MC cavity (Table 5). Analysis of the parameters that define the MC cavity and framework such as the cavity radius, the cross cavity Mn III -Mn III distance, the distance between adjacent Mn III ions, the cross cavity oxime oxygenoxime oxygen distance, and the distance of the Dy III ion from the oxime oxygen mean plane reveals that the identity of the bridging carboxylate has little impact on the overall metallacrown structure.

Database survey
[These parameters were determined as previously defined (Azar et al., 2014)]. Indeed, this is a hallmark of metallacrown chemistry, the ability to switch components of the molecular systems without significantly affecting the overall structure. This asset allows the systematic investigation of chemical and physical properties such as   Table 4 Hydrogen-bond geometry (Å , ). (19) 177 (10) Symmetry code: (i) Ày þ 1 2 ; x; z.

Figure 3
Intermolecular hydrogen bonding between the water molecules coordinated to the Na + ion of 1 and the interstitial DMF molecules. Each coordinated water molecule forms hydrogen bonds with two neighboring DMF molecules. For clarity, only the hydrogen atoms (white) of the water molecules and only two of the four DMF molecules are displayed. See Fig. 1 for additional display details. [Symmetry codes: magnetism or luminescence across a range of structures (Boron et al., 2016;Chow et al., 2016).

Refinement
Minor whole molecule disorder was detected for the metallacrown molecule (excluding the dysprosium and sodium ions) and all organic fragments, and the disorder was refined. The metallacrown is disordered by clockwise versus counterclockwise rotation orientation of the metallamacrocycle, as are the 2-propylvalerate anion and the interstitial DMF molecule (major and minor components). In addition, the main moiety alkyl chain of the 2-propylvalerate is disordered over two additional sites, and the main moiety interstitial DMF molecule is disordered over one additional site. The U ij components of ADPs for disordered atoms closer to each other than 2.7 Å were restrained to be similar (SIMU command of SHELXL). Occupancies were constrained to sum to unity for all sites using SUMP commands. The major and minor (Bmoiety) metallacrown units were restrained to have similar geometries. For the B-moiety benzene ring of the salicylhydroximate, the C atoms were restrained to be close to planar (FLAT command of SHELXL). For the 2-propylvalerate anion, the major (including the additional alkyl-chain disorder) and B-moieties were restrained to have similar geometries. The C-atom positions of the 2-propylvalerate were further restrained based on typical carbon-carbon bond distances and angles. The B-moiety carboxylate carbon atom (C8B) was restrained to planarity (CHIV 0 command of SHELXL).
For the interstitial DMF molecule, the N atom was restrained to be equidistant from both carbon atoms of the methyl groups. In addition, the major (including the additional disorder) and B-moieties were restrained to have similar geometries. Hydrogen-atom positions of the water molecule coordinated to the sodium ion were refined and O-H and HÁ Á ÁH distances were restrained to 0.84 (2) and 1.36 (2) Å , respectively. The water-O and H-atom positions were further restrained based on hydrogen-bonding considerations to the interstitial DMF molecule, and distances of all water H atoms to the sodium ion were restrained to be similar.
All other hydrogen atoms were placed in calculated positions and refined as riding on their carrier atoms with C-H distances of 0.95 Å for sp 2 carbon atoms and to 1.00, 0.99 and 0.98 Å for aliphatic C-H, CH 2 and CH 3 moieties, respectively. The U iso values for hydrogen atoms were set to a multiple of the U eq value of the carrying carbon or oxygen   (117) atom (1.2 times for C-H and CH 2 groups and 1.5 for water molecules and methyl groups). Subject to these conditions, the occupancy ratios refined as follows: main moiety metallacrown unit, 0.9030 (14) (14). Additional crystal data, data collection, and structure refinement details are summarized in Table 6.   Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Minor whole molecule disorder was detected for the metallacrown molecule and all organic fragments (excluding the dysprosium and sodium ions), and the disorder was refined. The metallacrown is disordered by clockwise vs counterclockwise rotation orientation of the metallacycle, as are the 2-propylvalerate anion and the interstitial DMF molecule (main moiety and B-moiety). In addition, the alkyl chain of the 2-propylvalerate of the main moiety is disordered over two additional sites, and the interstitial DMF molecule of the main moiety is disordered over one additional site. The Uij components of ADPs for disordered atoms closer to each other than 2.7 Angstrom were restrained to be similar (SIMU command of Shelxl). Occupancies were constrained to sum up to unity for all sites using SUMP commands. The major and minor (B-moiety) metallacrown units were restrained to have similar geometries. For the B-moiety benzene ring of the salicylhydroximate, the C atoms were restrained to be close to planar (FLAT command of Shelxl). For the 2-propylvalerate anion, the major (including the additional alkyl chain disorder) and B moieties were restrained to have similar geometries. The C atoms positions 2-propylvalerate were further restrained based on typical carboncarbon bond distances and angles. The B-moiety carboxylate carbon atom (C8B) was restrained to planarity (CHIV command of Shelxl). For the interstitial DMF molecule, the N atom was restrained to be equidistant from both carbon atoms of the methyl groups. In addition, the major (including the additional disorder) and B moieties were restrained to have similar geometries. H atom positions of the water molecule coordinated to the sodium ion were refined and O-H and H···H distances were restrained to 0.84 (2) and 1.36 (2) Angstrom, respectively. The water O and H atom positions were further restrained based on hydrogen bonding considerations to the interstitial DMF molecule and distances of all water H atoms to the sodium ion were restrained to be similar. All other hydrogen atoms were placed in calculated positions and refined as riding on their carrier atoms with C-H distances of 0.95 Angstrom for sp2 carbon atoms. The Uiso values for hydrogen atoms were set to a multiple of the Ueq value of the carrying carbon atom (1.2 times for sp2 hybridized carbon atoms, 1.5 for water molecules and methyl groups). Subject to these conditions the occupancy ratios were refined as follows: main metallacrown unit: 0.9030 (14)  0.120 (6) 0.123 (7) 0.082 (6) 0.011 (6) 0.025 (6) −0.011 (6) C14D 0.127 (7) 0.121 (7) 0.091 (7) 0.014 (7) 0.022 (6) −0.012 (6) C15D 0.140 (13) 0.131 (13)  0.042 (7) 0.032 (7) 0.075 (8) 0.003 (6) 0.009 (7) 0.007 (7)  O2B 0.048 (6) 0.035 (6) 0.073 (7) −0.002 (6) 0.006 (6) 0.001 (6)  O3B 0.054 (7) 0.047 (7) 0.074 (7) −0.004 (7) 0.009 (7) −0.005 (7)  N1B 0.052 (7) 0.040 (7) 0.070 (7) −0.006 (6) 0.010 (7) 0.000 (7)  0.057 (7) 0.045 (7) 0.084 (7) −0.007 (7) 0.011 (7) −0.002 (7)  C5B 0.058 (7) 0.046 (7) 0.085 (7) −0.012 (7) 0.015 (7) 0.002 (7)  C6B 0.055 (7) 0.043 (7) 0.081 (7) −0.007 (7) 0.013 (7) −0.001 (7)  0.118 (7) 0.112 (7) 0.083 (7) 0.012 (7) 0.020 (7) −0.016 (7)