Crystal structure of a TbIII–CuII glycinehydroxamate 15-metallacrown-5 sulfate complex

The metallamacrocyclic core of the discrete hexanuclear 15-metallacrown-5 complex [TbCu5(GlyHA)5(H2O)6.5(SO4)]2(SO4)·6H2O contains five copper(II) ions linked by five glycinehydroxamate (GlyHA2–) dianions with a square-antiprismatically octacoordinate terbium(III) ion in the centre. The positive charge of the 15-metallacrown-5 [TbCu5(GlyHA)5]3+ core is compensated by bidentate and non-coordinated sulfate anions.


Figure 2
Structure of the [TbCu 5 (GlyHA) (4) with -values (Addison et al., 1984) ranging from 0.07 to 0.13]. As a result of the disorder of the O19 water molecule between two symmetry-equivalent positions with occupancy factors of 0.5, 50% of the Cu2 atoms in 1 have square-planar coordination environments, while the other 50% possess a square-pyramidal coordination [Cu2-O19 = 2.409 (10), = 0.022 (Addison et al., 1984)]. The terbium(III) ions at the centres of the [Cu 5 (GlyHA) 5 ] metallamacrocyclic cores in 1 are bound by five hydroxamate oxygen atoms. The Tb-O eq bond lengths are typical for 15-metallacrown-5 complexes and range from 2.370 (3) to 2.430 (3) Å (Stemmler et al., 1999;Pavlishchuk et al., 2011;Katkova et al., 2015a;Meng et al., 2016). The coordination environment of the Tb 3+ ion is completed to an octacoordination level via the two oxygen atoms O11 ion. An analysis of selected structural parameters for complex 1 and those of isomorphous compounds with other Ln III ions (Table 2) reveals the influence of the lanthanide contraction. Similar behaviour was found in other series of lanthanide(III) containing metallamacrocycles (Pavlishchuk et al., 2011;Zaleski et al., 2011). According to Shape 2.1 (Casanova et al., 2005) calculations (Fig. 3, Table 3), the coordination geometry of the Tb III ion in 1 is a square antiprism (D 4d ), which is of particular interest with respect to potential generation of lanthanide(III)containing SMMs (Liu et al., 2018). The deviations from an idealized square-antiprismatic geometry in the [LnCu 5 (GlyHA) 5 (SO 4 )(H 2 O) 6.5 ] 2 (SO 4 ) complexes decrease with reduction of the deviation of the Ln III ion from the mean plane of the metallacrown core, which parallels the ionic radii of the Ln III ions (Table 3). It may be noted that, in the case of a series of related 15-metallacrown-5 complexes with octacoordinate Ln III ions containing bidentate carbonates or acetates instead of sulfates, the coordination of the lanthanide ions is triangular dodecahedral (D 2d ) ( Table 3).

Figure 3
The Tb III coordination sphere geometry in 1.
The Ln-O distances, Ln-Cu separations and deviations of the Ln III ions from the Cu 5 planes of the metallamacrocycles trend with the lanthanide contraction in all members of the isomorphous [LnCu 5 (GlyHA) 5 ] 3+ series. However, there are some minor differences in the observed values for a given Ln III ion, depending on the coordinated bidentate counteranion, which is likely associated with the different planarities of the {LnCu 5 } 3+ cores (Table 2).

Synthesis and crystallization
Complex 1 was synthesized and crystallized according a general procedure described previously (Pavlishchuk et al., 2011). Single crystals were obtained by slow evaporation from an aqueous solution of 1.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. The structure is isomorphous with its Dy, Eu, Gd, Ho, Nd, Pr analogues (Pavlishchuk et al., 2011) and was solved by isomorphous replacement. The O19 water molecule is disordered over two mutually exclusive positions across an inversion center and was refined as half occupied.
The non-coordinated sulfate ion is located on an inversion center and the oxygen atoms are disordered over two sets of positions with half occupancy. C-H bond distances were constrained to 0.99 for aliphatic CH 2 moieties. N-H bond distances were constrained to 0.91 Å for pyramidal (sp 3 -hybridized) ammonium NH 2 + groups. Water H-atom positions were refined, and O-H distances were restrained to 0.84 (2) Å . The HÁ Á ÁH distances within the O23 and O24 water molecules were further restrained to 1.35 (2) Å . U iso (H) values were set to kU eq (C/N/ O) with k =1.5 for OH, and 1.2 for CH 2 and NH 2 + units, respectively. Data collection: APEX3 (Bruker, 2018); cell refinement: SAINT (Bruker, 2018); data reduction: SAINT (Bruker, 2018); 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). 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 ismorphous with its Dy, Eu, Gd, Ho, Nd, Pr analogues (AVP85_10mz121, AVP355_10mz172, AVP621_09mz411 and AVP629_10mz194, AVP65_10mz125 and AVP651_10mz191, AVP70_10mz147, AVP75_10mz148 and AVP754_10mz650), and was solved by isomorphous replacement. The water molecule of O19 is disordered over two mutually exclusive positions across an inversion center and was refined as half occupied. The non-coordinated sulfate ion is located on an inversion center and the oxygen atoms are disordered over two sets of positions with half occupancy. Water H atom positions were refined and O-H distances were restrained to 0.84 (2) Angstrom, respectively. Some H···H distances were further restrained to 1.35 (2) Angstrom.