The crystal structures of {LnCu5}3+ (Ln = Gd, Dy and Ho) 15-metallacrown-5 complexes and a reevaluation of the isotypic EuIII analogue

The crystal structures of three new isomorphous 3d–4f 15-metallacrown-5 complexes, [LnCu5(GlyHA)5(CO3)(NO3)(H2O)5]·xH2O (Ln III = Gd (1, x = 3.5); Dy (2, x = 3.28) and Ho (3, x = 3.45)), were determined. Structural details of the previously reported isotypic EuIII analogue were reinterpreted.


Chemical context
The numerous studies of 3d-4f metallamacrocyclic complexes in the last few decades arise from their potentially interesting catalytic (Griffiths & Kostakis, 2018), luminescence (Jankolovits et al., 2011;Li et al., 2017) and magnetic properties (Dhers et al., 2016;Zangana et al., 2014). In addition, a number of heteropolynuclear metallacrown complexes have been shown to possess single molecule magnetic (SMM) behaviour (Ostrowska et al., 2016;Wang et al., 2019), bright luminescence with high quantum yields (Nguyen et al., 2018;Martinić et al., 2017) and the ability to serve as building blocks for the generation of supramolecular assemblies and coordination polymers (Pavlishchuk et al., 2014(Pavlishchuk et al., , 2017b. The utilization of heteronuclear cationic 15-metallacrown-5 complexes as initial building blocks has also led to porous structures that are able to absorb various guest molecules (Lim et al., 2010). The selection of the initial building blocks with labile counteranions (e.g. nitrates) is crucial for the creation of coordination ISSN 2056-9890 polymers with porous structures. Some of the products of the reactions between glycinehydroxamate-derived 15-metallacrown-5 complexes and polycarboxylates contain carbonate anions (Pavlishchuk et al., 2014(Pavlishchuk et al., , 2017b, which block the apical positions of the Ln III ions and lead to the formation of discrete assemblies instead of coordination polymers. The presence of carbonate anions in such complexes was associated with the capture of atmospheric carbon dioxide (Pavlishchuk et al., 2014(Pavlishchuk et al., , 2017b. The first examples of 15-metallacrown-5 complexes were reported by Pecoraro and coworkers in 1999 (Stemmler et al., 1999). One of the reported complexes, a Eu III -Cu II glycinehydroxamate metallacrown, contains the [CuGlyHA] 5 core and encapsulates an Eu III ion through coordination to five hydroxamate oxygen atoms. It was reported that the positive charge of the 15-metallacrown-5 unit, [EuCu 5 (GlyHA) 5 ] 3+ , was partly compensated by two nitrate anions coordinated to copper(II) and europium(III). To fully compensate the positive charge of the [EuCu 5 (GlyHA) 5 ] 3+ unit, an oxygen species coordinated apically to Eu III was assigned as a hydroxide anion, to give a reported overall composition [EuCu 5 (Gly-HA) 5 (OH)(NO 3 ) 2 (H 2 O) 4 ]Á3.5H 2 O. The high R-factor of 12.3% for the structure was attributed to the presence of disordered water molecules in the crystal structure (Stemmler et al., 1999). We report here the crystal structures of three isostructural 15-metallacrown-5 complexes, [LnCu 5 (GlyHA) 5 -(CO 3 )(NO 3 )(H 2 O) 5 ]ÁxH 2 O (Ln III = Gd (1, x = 3.5); Dy (2, x = 3.28) and Ho (3, x = 3.45)). Based on the high-quality diffraction data collected for 1-3, a new formula of [EuCu 5 -(GlyHA) 5 (CO 3 )(NO 3 )(H 2 O) 5 ]Á3.5H 2 O is proposed for the previously reported Eu compound.

Structural commentary and supramolecular features
Complexes 1-3, and the previously reported europium analogue (Stemmler et al., 1999), are isotypic based on the unit-cell parameters obtained (Table 1) and the structure refinement results. The b and c lattice parameters and the unitcell volumes for these complexes decrease slightly across the lanthanide series as a result of the lanthanide contraction (Pavlishchuk et al., 2011(Pavlishchuk et al., , 2017b(Pavlishchuk et al., , 2018Stemmler et al., 1999;Zaleski, et al., 2011). All four compounds crystallize in the space group P1 and contain two molecular metallamacrocyclic complexes per unit cell related to each other through a centre of inversion (Fig. 1). For the convenience of structure description, a common atom-numbering scheme is adopted for 1-3.
repeating fragment [CuGlyHA], formed via bridging coordination of GlyHA 2À dianions to two adjacent copper(II) ions, forming two five-membered chelate rings (Fig. 2). The coordination environment of the copper(II) ions in 1-3 consists of two nitrogen atoms (from amino and hydroxamate groups) and two oxygen atoms (from carbonyl and hydroxamate groups) in their basal planes. The Cu-O and Cu-N bond lengths in 1-3 are typical for hydroxamate metallacrown complexes (Tables 2-4) and are comparable with the values previously reported for the Eu III analogue (Stemmler et al., 1999). All the copper(II) ions in 1-3 are pentacoordinate, with N 2 O 3 donor sets in slightly distorted square-pyramidal coordination arrangements [ values (Addison et al., 1984) fall in the range of 0. . For all the complexes, a pronounced Jahn-Teller-like distortion is observed, with the Cu-N and Cu-O bonds from glycinehydroxamate in the plane of the metallacrown unit being substantially shorter than the Cu-O bond of the fifth coordination site, the apical position. This site for the Cu2 atom is in each case occupied by the oxygen atom O15 from the monodentate nitrate anions  Table 1 Comparison of single-crystal data and structure refinement details for complexes 1-3 with those of their earlier reported Eu III analogue (CCDC127569, Stemmler et al., 1999). CCDC127569 Complex 1
The two Ln III ion apical positions in 1-3 are occupied by oxygen atoms O12 [2.317 (11)

Figure 3
The coordination environment of the Gd III ion in 1.

Table 11
Hydrogen-bond geometry (Å , ) for complex 2.  (3) 3.065 (7) 158 (6) (7) 3.033 (18) (5) 163 (6) with refined occupancy factors of 0.499 (11), 0.280 (14) and 0.445 (11) in 1-3, respectively (see the Refinement section for details). Bond distances within the anion are biased because of the disorder, so no assignment of nitrate vs carbonate can be made based on expected N-O or C-O bond distances. However, despite this disorder involving the anions neighbouring the partially occupied water molecule, the nature of the entity as a carbonate anion is clearly resolved in difference electron-density maps. Replacement of the carbonate carbon atom, C11, with a nitrogen atom results only in a marginal increase in R value (e.g. 3.10 vs 3.07% for compound 2). Thermal parameters of the 'nitrogen' atoms do however become unreasonably large, compared to the neighbouring oxygen atoms, and a positive residual electron density is clearly visible around the central atoms of the anion when refined as nitrogen (Fig. 6). For the other O 3 X anion, coordinated to Cu4, the opposite observation can be made, and this anion matches the electron density requirements of a nitrate anion.
In summary, we have synthesized three new metallamacrocyclic (Ln = Gd, Dy and Ho) complexes with glycinehydroxamate, which are isotypic with the first representative of the 15-metallacrown-5 family reported in 1999. The better quality of the new structural data allow us to propose an alternative composition [LnCu 5 (GlyHA) 5 (CO 3 )(NO 3 )-(H 2 O) 5 ]ÁxH 2 O [Ln III = Gd (1, x = 3.5), Dy (2, x = 3.28) and Ho (3, x = 3.45)] for this series of compounds and the previously reported Eu complex (x = 3.5). The cationic charge of the {LnCu 5 } 3+ metallamacrocyclic cores in 1-3 is compensated by a monodentate nitrate anion coordinated to a Cu II ion and a bidentate carbonate ion linked to the Ln III ions. The presence of capping carbonate anions in metallacrown building blocks can prevent the formation of coordination polymers based on the metallacrown complex.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 13. The three structures are isotypic and were refined using a common structural model.
All carbon-and nitrogen-bound H atoms, while observed in difference density maps, were placed in calculated positions, with C-H distances of 0.99 Å and N-H distances of 0.91 Å . All H-atom positions of the ordered water molecules were clearly resolved in difference electron-density maps and their positions were refined with O-H and HÁ Á ÁH distances restrained to 0.84 (2) and 1.36 (2) Å , respectively. The H-atom positions of the disordered water moieties were further restrained based on hydrogen-bonding considerations. In the research communications Table 12 Hydrogen-bond geometry (Å , ) for complex 3.  (3) 160 (5) (3) 3.060 (9) 163 (5) (6) 3.088 (11) 125 (6) (4) 165 (5) final refinement cycles, the partially occupied H atoms were set to ride on their carrier oxygen atoms. U iso values of all H atoms were set to a multiple of their respective carrier atom, with U iso (H) = 1.2U eq (C/N) or 1.5U eq (O). In all three structures, one water molecule position is partially occupied, inducing disorder for the nearby carbonate anion. The two disordered carbonate moieties were restrained to have similar geometries (using SHELXL SAME restraints, esd = 0.02 Å ). U ij components of ADPs for disordered atoms closer to each other than 2.0 Å were restrained to be similar within a standard deviation of 0.01 Å 2 (SIMU restraint of SHELXL). In 1 and 3, the distance of the water oxygen to one of the carbonate oxygen atoms was restrained to be at least 2.80 (2) Å for the moiety that contains the water molecule [2.75 (2) Å for 2]. Subject to these conditions, the occupancy ratios refined to 0.499 (11) to 0.501 (11) for 1, 0.280 (14) to 0.720 (14) for 2 and 0.445 (11) to 0.555 (11) for 3.
There is an indication of additional disorder involving the partially ordered water molecule nearby the carbonate ion. This additional disorder is not well enough resolved to be independently refined and may cause the B alerts in the CIF files of 1-3. We opted to not attempt to refine additional potentially highly ambiguous disorder.   (15), 11.5054 (15), 13.2983 (10) 11.1083 (5), 11.4991 (5), 13.2894 (6) 11.2027 (9), 11.4955 (9)

Computing details
For all structures, data collection: APEX3 (Bruker, 2017); cell refinement: SAINT (Bruker, 2017); data reduction: SAINT (Bruker, 2017); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015), SHELXLE (Hübschle et al., 2011); software used to prepare material for publication: publCIF (Westrip, 2010).  (15) 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. A water molecule is partially occupied, inducing disorder for the nearby carbonate anion. The two disordered moieties were restrained to have similar geometries. Uij components of ADPs for disordered atoms closer to each other than 2.0 Angstrom were restrained to be similar. The distance of the water oxygen to one of the carbonate oxygen atoms was restrained to be at least 2.8 Angstrom for the moiety that contains the water molecule. Water H atom positions were refined and O-H and H···H distances were restrained to 0.84 (2) and 1.36 (2) Angstrom, respectively. The water H atom positions of the disordered moiety were further restrained based on hydrogen bonding considerations. Subject to these conditions the occupancy ratio refined to 0.499 (11) to 0.501 (11).

Pentaaquacarbonatopentakis(glycine hydroxamato)nitratopentacopper(II)dysprosium(III) 3.28-hydrate (Complex_2)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.99 e Å −3 Δρ min = −1.26 e Å −3 Extinction correction: SHELXL-2018/3 (Sheldrick 2015), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.00073 (12) 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. The structure is isotypic to its Gd analogue, AVP815, and was solved by isomorphous replacement. A water molecule is partially occupied, inducing disorder for the nearby carbonate anion. The two disordered moieties were restrained to have similar geometries. Uij components of ADPs for disordered atoms closer to each other than 2.0 Angstrom were restrained to be similar. The distance of the water oxygen to one of the carbonate oxygen atoms was restrained to be at least 2.75 Angstrom for the moiety that contains the water molecule. Water H atom positions were refined and O-H and H···H distances were restrained to 0.84 (2) and 1.36 (2) Angstrom, respectively. The water H atom positions of the disordered moiety were further restrained based on hydrogen bonding considerations. In the final refinement cycles the partially occupied H atoms were set to ride on their carrier oxygen atom. Subject to these conditions the occupancy ratio refined to 0.280 (14) to 0.720 (14).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. ( where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 2.80 e Å −3 Δρ min = −2.27 e Å −3 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. Solved by isomorphous replacement from its Gd analogue. A water molecule is partially occupied, inducing disorder for the nearby carbonate anion. The two disordered moieties were restrained to have similar geometries. Uij components of ADPs for disordered atoms closer to each other than 2.0 Angstrom were restrained to be similar. The distance of the water oxygen to one of the carbonate oxygen atoms was restrained to be at least 2.8 Angstrom for the moiety that contains the water molecule. Water H atom positions were refined and O-H and H···H distances were restrained to 0.84 (2) and 1.36 (2) Angstrom, respectively. The water H atom positions of the disordered moiety were further restrained based on hydrogen bonding considerations. Subject to these conditions the occupancy ratio refined to 0.445 (11) to 0.555 (11).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (