Novel three-dimensional coordination polymer of 2-(1,3,5-triaza-7-phosphoniatricyclo[3.3.1.13,7]decan-7-yl)ethanoic acid with silver(I) tetrafluoroborate

A three-dimensional coordination polymer of 2-(1,3,5-triaza-7-phosphoniatricyclo[3.3.1.13,7]decan-7-yl)ethanoate with silver(I) tetrafluoroborate was fully characterized.

The chemical shift of the phosphorus atom in CP ( = À37.5 ppm in D 2 O) was the same as that in the free ligand. Similar to the hexafluorophosphate, tosylate (tos) and triflate (OTf) derivatives (Udvardy et al., 2021), the 1 H-NMR spectrum showed differences between the P + -CH 2 -N and N-CH 2 -N signals, which clearly indicated the coordination of the silver ions to the nitrogen donor atoms of the L ligand. The

Structural commentary
The molecular structure of the title compound is shown in Fig. 2. The CP crystallized in the monoclinic Cc space group. The asymmetric unit consists of a silver(I) cation, a zwitterionic L ligand and a BF 4 À counter-ion, in which the N,N 0 ,O,O 0 coordination mode of the silver(I) ions creates a 3D coordination architecture (Fig. 2).
In the CP, the central Ag + ion is coordinated by an L ligand via two carboxylate oxygen atoms [Ag1 2 -O11 = 2.594 (9) Å and Ag1 2 -O12 = 2.298 (8) Å ] and two nitrogen atoms from two adjacent PTA moieties of L [Ag1-N1 = 2.225 (7) Å and Ag1 1 -N3 = 2.505 (7) Å ]. The N1-Ag-N3 3 and O11 4 -Ag-O12 4 bond angles are 119.6 (3) and 52.9 (2) , respectively. Selected bond lengths and bond angles are presented in the supporting information. The coordination geometry exhibits a distorted tetrahedral shape ( 4 = 0.65 and 4 ' = 0.66; Yang et al., 2007;Okuniewski et al., 2015), in which the Ag I ion is located at the centre. The space between the 3D polymer backbones is occupied by the BF 4 À counter-ions (Fig. 3). The chemical composition was also determined by elemental analysis, which shows a good agreement with the SC-XRD results (see Synthesis and crystallization). (a) Packing arrangement of the three-dimensional structure of the CP in the crystal viewed along the crystallographic a axis. The coordination sphere is labelled and highlighted by a ball-and-stick model. Hydrogen atoms are omitted for clarity. (b) Selected hydrogen-bond geometry in the CP showing the weak C-HÁ Á ÁF and C-HÁ Á ÁO secondary interactions, as well as the Ag1Á Á ÁF3 interaction. For symmetry codes, see Table 1. Table 1 Hydrogen-bond geometry (Å , ). Schematic representation of the formation of the title compound.

Supramolecular features
As a result of the lack of primary H-donor groups, no classical hydrogen bonds are found in the crystal structure of the title coordination polymer. The main intermolecular interactions between the molecules in the crystal are weak C-HÁ Á ÁF and C-HÁ Á ÁO type hydrogen bonds. The BF 4 À anion is generally classified as a non-coordinating anion owing to its weak Lewis base properties (Grabowski, 2020). These secondary interactions play a major role in stabilizing the crystal lattice by connecting the molecular units to each other, which results in a 3D coordination polymer. All of the fluorine atoms of a BF 4 À counter-ion are connected to at least one C-H hydrogen atom by a weak C-HÁ Á ÁF type hydrogen bond. The shortest C-HÁ Á ÁF distance is found for the C2-H2BÁ Á ÁF3 interaction [C2Á Á ÁF3 = 3.183 (13) Å ], where the F3 atom of the BF 4 À counter-ion is also able to coordinate to the central Ag + ion with a distance of 3.010 (11) Å (Fig. 3). This ionic attraction between the Ag + and BF 4 À ions is strong enough to affect the arrangement of part of the whole complex molecule and form a bent 3D structure. In comparison, the value of the longest C-HÁ Á ÁF distance is 3.417 (14) Å (C4-H4BÁ Á ÁF2, Fig. 3) owing to the rigid PTA cage, which is unable to change its conformation. There are numerous examples in the literature of where the C-HÁ Á ÁF distances were investigated in the presence of BF 4 À counter-ions [i.e. BIXBIT03 (Emge et al., 1986) and SUXHID01 (Albinati et al., 2010)]. In case of the bis[ 2 -1,1 0 -naphthalene-1,8-diyl-bis(1H-pyrazole)]tris(acetonitrile)disilver(I) bis(BF 4 ) acetonitrile solvate structure (OGINOI; Liddle et al., 2009), it was found that the typical CÁ Á ÁF distances are between 3.179 (2) and 3.406 (3) Å , which shows a good agreement with our results. The carboxylate oxygen atoms in the title CP are also able to form weak C-HÁ Á ÁO type interactions with the C-H atoms of the complex molecule. Their atomic distances can also be compared to the C-HÁ Á ÁF secondary interactions. An intramolecular hydrogen bond also helps to form a bent 3D molecular structure for the CP [C2Á Á ÁO12 = 2.812 (12) Å ]. For selected hydrogen-bond distances and angles see Fig. 3b and Table 1. The considerably high calculated density (2.102 Mg m À3 ) and KPI (Kitaigorodskii packing index) of 74.2% (Spek, 2020) indicate the tight packing arrangement of the molecules, resulting in no residual solvent-accessible voids in the crystal structure. Ag I complex is able to form a 3D coordination polymer owing to the relatively small size of the BF 4 À counter-ion, which is able to occupy a smaller space compared to the PF 6 À , triflate or tosylate anions. These results show how a counter-ion can influence the packing arrangement and the coordination mode of an [(AgL)X] type polymer.
CP: With the exclusion of light, 4 mL aqueous solution containing 194.7 mg (1 mmol) AgBF 4 was added to an aqueous solution (4 mL) of L (100 mg, 0.44 mmol). The reaction mixture was stored at 278 K. After two days, the CP was formed as colourless crystals, which were separated by filtration and dried. Yield

Crystal data
[Ag (C 9  Absolute structure: Classical Flack method preferred over Parsons because s.u. lower Absolute structure parameter: 0.13 (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.