On the Importance of H‑Bonding Interactions in the Enclathration of Boric Acids in Na(I) Polymers: Experimental and Theoretical Studies

: Two Na(I) coordination polymers, namely, {Na(BA) 2 ( µ ‑H 2 O) 2 } n {adp} n ( 1 ) and {[Na 2 ( µ ‑ BA)( µ ‑fum)( µ ‑H 2 O) 4 ](BA)} n ( 2 ) (where, BA = boric acid, adp = adipic acid, fum = fumarate),were prepared and characterized using elemental analysis, TGA, FT‑IR, and single‑crystal X‑ray diffrac‑ tion techniques. Various unconventional supramolecular interactions, i.e., CH ··· HC and parallel CO ··· CO interactions, stabilize the layered assembly of compound 1 . Interesting dual enclathration of BA molecules within the supramolecular host cavities formed by O‑H ··· O and C‑H ··· C interactions stabilizes the crystal structure of compound 2 . The H‑bonding interactions in 1 and 2 were further studied theoretically using the quantum theory of atoms in molecules (QTAIM) and the noncovalent interaction plot (NCI Plot) computational tools. The energy of the H‑bonds was estimated using the potential energy density at the bond critical points. Theoretical calculations confirmed the presence of O‑H ··· O H‑bonding interactions in both compounds, forming structure‑guiding R 22 ( 8 ) synthons relevant for the stability of the compounds.


Introduction
Coordination polymers represent the supramolecular architecture of metal ions and organic moieties that extends in association with covalent bonding, as well as supramolecular contacts [1][2][3].In the current research era, the design and synthesis of coordination polymers involving supramolecular interactions has attracted immense attention owing to their interesting physical, chemical properties, and potential applications [4,5].Although coordination polymers involving transition metals bridged by organic ligands have been well explored [6,7], examples of polymers with s-block elements such as sodium are still scarce in the literature.The strategic synthesis of coordination polymers of such elements is still challenging, which may be due to various factors such as varying coordination number, size of the binding partners, and electrostatic interactions between the ligands and the metal ions [8].
The design of boron-based compounds has received a great deal of interest because of their potential utilities as boron-containing drugs and materials for medical diagnostics [9,10].Boron compounds can be used as modulators for the bioactivity of biomolecules, in boron capture neutron therapy (BNCT) for drug delivery, and in molecular modeling of drug design [11,12].Boric acid has been effectively utilized as a building block to construct a variety of compounds with interesting structural topologies [13,14].Cebula et al. recently highlighted the importance of supramolecular assemblies of boron-mediated anionic clusters and their applications in biological fields [15].In an organic crystal of 4-Crystals 2023, 13, 895 2 of 15 pyridinylboronic acid, B•••Cl σ-hole triel bonding interactions were observed, established using various computational tools [16].
To understand the role of noncovalent contacts in self-assembly processes, innumerable efforts have been undertaken due to their potential applications in a wide range of fields such as catalysis, crystal engineering, pharmaceutical design, molecular biology, and molecular recognition [17][18][19].Although supramolecular interactions are weaker than covalent bonds, their large numbers and cumulative effects make them potential candidates in the design of crystal structures [20,21].H-bonding interactions can be considered as the most common which play crucial roles in molecular self-assembly processes [22], as well as in the stabilization of biomolecules such as -DNA and proteins (Figure 1) [23].In the stabilization of metal-organic compounds, the dipolar interactions between carbonyl groups (CO•••CO) are also equally important in the stability of the crystal structures [24].
Crystals 2023, 13, x FOR PEER REVIEW 2 of 15 anionic clusters and their applications in biological fields [15].In an organic crystal of 4pyridinylboronic acid, B•••Cl σ-hole triel bonding interactions were observed, established using various computational tools [16].
To understand the role of noncovalent contacts in self-assembly processes, innumerable efforts have been undertaken due to their potential applications in a wide range of fields such as catalysis, crystal engineering, pharmaceutical design, molecular biology, and molecular recognition [17][18][19].Although supramolecular interactions are weaker than covalent bonds, their large numbers and cumulative effects make them potential candidates in the design of crystal structures [20,21].H-bonding interactions can be considered as the most common which play crucial roles in molecular self-assembly processes [22], as well as in the stabilization of biomolecules such as -DNA and proteins (Figure 1) [23].In the stabilization of metal-organic compounds, the dipolar interactions between carbonyl groups (CO•••CO) are also equally important in the stability of the crystal structures [24].The saturated aliphatic dicarboxylate moieties, as important flexible bridging ligands, can adopt conformational and coordination versatilities owing to their singlebonded carbon chains, which can be considered for the development of interesting metalorganic compounds [25,26].The dicarboxylate anions can exhibit multiple coordination motifs such as uni-bidentate, bis-monodentate, bis-bidentate, tridentate, and tetradentate etc., thereby interconnecting metal centers to form polynuclear complexes [27,28].Saturated dicarboxylic acids also serve as suitable H-bonding acceptors [29,30], resulting in the development of bridging metal-organic compounds with various desired self-assembled architectures [31,32].As a consequence, adipic acid has evolved as a potential bridging ligand to form interesting coordination polymers with potential applications [33][34][35].The dicarboxylate groups of fumarate anion (an unsaturated dicarboxylate) also have the ability to coordinate with the metal centers in multidentate fashion [36].As a result, metal fumarate complexes have been explored with interesting structural topologies [37].In recent times, a few boric acid-mediated metal-organic compounds have also been reported with desired applications [15,38].
In order to visualize the role of supramolecular interactions in polymeric complexes, we report herein the synthesis and crystal structures of two Na(I) polymers, namely, {Na(BA)2(µ-H2O)2}n{adp}n ( 1  The saturated aliphatic dicarboxylate moieties, as important flexible bridging ligands, can adopt conformational and coordination versatilities owing to their single-bonded carbon chains, which can be considered for the development of interesting metal-organic compounds [25,26].The dicarboxylate anions can exhibit multiple coordination motifs such as uni-bidentate, bis-monodentate, bis-bidentate, tridentate, and tetradentate etc., thereby interconnecting metal centers to form polynuclear complexes [27,28].Saturated dicarboxylic acids also serve as suitable H-bonding acceptors [29,30], resulting in the development of bridging metal-organic compounds with various desired self-assembled architectures [31,32].As a consequence, adipic acid has evolved as a potential bridging ligand to form interesting coordination polymers with potential applications [33][34][35].The dicarboxylate groups of fumarate anion (an unsaturated dicarboxylate) also have the ability to coordinate with the metal centers in multidentate fashion [36].As a result, metal fumarate complexes have been explored with interesting structural topologies [37].In recent times, a few boric acid-mediated metal-organic compounds have also been reported with desired applications [15,38].
In order to visualize the role of supramolecular interactions in polymeric complexes, we report herein the synthesis and crystal structures of two Na(I) polymers, namely, {Na(BA) 2 (µ-H 2 O) 2 } n {adp} n (1)  H•••H-C interactions provides rigidity to the crystal structure of compound 2. To explore the energetic features and the characteristics of H-bonding interactions, we use QTAIM and NCI plot computational tools.The strength of the H-bonding interactions is investigated using the potential energy density in QTAIM, revealing the importance of R 2 2 (8) synthons in the crystal structures.

Materials and Methods
The chemicals used in the present study, namely, sodium hydroxide, boric acid, adipic acid, and fumaric acid, were purchased from commercial sources and used as received.We prepared the disodium salt of fumaric acid using standard laboratory methods.A Perkin Elmer 2400 Series II CHNS/O analyzer was used to carry out the elemental analysis of the compounds.KBr phase FT-IR spectra were recorded using a Bruker Alpha Infrared spectrophotometer (resolution = 4 cm −1 ; number of scans = 16), in the wavenumber range 4000-500 cm −1 .Thermogravimetric studies were carried out under the flow of N 2 gas using a Mettler Toledo TGA/DSC1 STAR e system at a heating rate of 10 • C•min −1 .The TGA curves were recorded in the temperature range 25-1000 • C with 2 µg resolution.

Materials and Methods
The chemicals used in the present study, namely, sodium hydroxide, boric acid, adipic acid, and fumaric acid, were purchased from commercial sources and used as received.We prepared the disodium salt of fumaric acid using standard laboratory methods.A Perkin Elmer 2400 Series II CHNS/O analyzer was used to carry out the elemental analysis of the compounds.KBr phase FT-IR spectra were recorded using a Bruker Alpha Infrared spectrophotometer (resolution = 4 cm −1 ; number of scans = 16), in the wavenumber range 4000-500 cm −1 .Thermogravimetric studies were carried out under the flow of N2 gas using a Mettler Toledo TGA/DSC1 STAR e system at a heating rate of 10 °C•min −1 .The TGA curves were recorded in the temperature range 25-1000 °C with 2 µg resolution.

Crystallographic Data Collection and Refinement
Single-crystal XRD data of the compounds were recorded using a Bruker D8 Venture diffractometer with a Photon III 14 detector, using an Incoatec high-brilliance IµS DIA-MOND Cu tube.The Bruker APEX4 program was used for the data reduction and cell refinements [39].Scaling and merging of the datasets of the wavelength were carried out using SADABS [39].Crystal structures of the compounds were solved using the direct method and refined using the full-matrix least-squares technique with SHELXL-2018/3 [40] inWinGX [41] software.The non-hydrogen atoms of the crystal structures were refined with anisotropic thermal parameters using full-matrix least-squares calculations on F 2 .Hydrogen atoms were inserted at calculated positions and refined as riders.Diamond 3.2 software was used to draw the compounds [42].Crystallographic data of the compounds are presented in Table 1.CCDC 2213579 and 2213580 contain the supplementary crystallographic data for the compounds 1 and 2 respectively.These data can be obtained free of charge at http://www.ccdc.cam.ac.uk or from the Cambridge Crystallographic Data Center (12 Union Road, Cambridge CB2 1EZ, UK; Fax: (+44) 1223-336-033; or E-mail: deposit@ccdc.cam.ac.uk).

Theoretical Methods
The single-point calculations were carried out using the Turbomole 7.7 program [43] and the PBE0-D3/def2-TZVP [44][45][46] level of theory.The crystallographic coordinates were used to evaluate the interactions in compounds 1 and 2 since we were interested in studying the H-bonding interactions in the solid state.Since the structures were polymeric, finite models extracted from the solid-state structures were selected to study the formation of the H-bonding interactions.The Bader's "Atoms in molecules" theory (QTAIM) [47] and noncovalent interaction plot (NCI Plot) [48] were used to study the interactions discussed herein using the Multiwfn program [49] and represented using the VMD visualization software [50].For the calculation of the H-bond energies, we used the equation proposed by Espinosa et al. (E = ½Vr) [51].(1) was synthesized via a reaction involving NaOH, BA, and adp in 1:2:1 ratio at room temperature in deionized water.Similarly, {[Na 2 (µ-BA)(µfum)(µ-H 2 O) 4 ](BA)} n (2) was prepared by reacting NaOH, BA, and Na 2 -fum in 2:2:1 ratio at room temperature in deionized water.Compounds 1 and 2 were soluble in water, as well as common organic solvents.The crystal structure of compound 2 was already reported by Ozer et al. [52] (Table S1).However, we synthesized the compound by employing a comparatively simple synthetic pathway at room temperature.We also explored the detailed structural characteristics of the compound, which revealed the unusual dual enclathration of BA moieties in the supramolecular host cavity of the compound (vide infra).Moreover, the energetic features of the H-bonding interactions were investigated in the crystal structure using computational tools (vide infra).

Crystal Structure Analysis
The molecular structure of compound 1 is depicted in Figure 2. Table S2 contains the bond lengths and bond angles around the Na(I) centers.The compound crystallized in the triclinic P1 space group.Compound 1 comprises two 1D polymeric chains.The first one possesses Na(I) centers bridged by two water molecules.Two BA molecules are also coordinated with the Na(I) centers.Thus, each Na(I) center is hexacoordinated with two O atoms from the BA molecules (O2B and O2B') and four Oatoms from the bridged water molecules (O1W, O1W, O1W', and O1W'').The coordination geometry around each Na(I) center is ideal octahedron, where the axial positions are filled by two bridged water molecules, whereas the equatorial sites are occupied by the other bridged water molecules and the two Oatoms of BA moieties.Moreover, the second 1D polymeric chain holds adp molecules bridged by the hydrogen atom of adp (H3A).X-ray crystallographic analysis indicates that the 1D polymeric chain of Na(I) centers possesses a crystallographic inversion center at the midpoint of two neighboring Na(I) centers.The 1D polymeric chain of adp also possesses crystallographic inversion at the midpoint of the C-C bond of adp.
Figure 5 depicts the molecular structure of compound 2. Tables S3 and S4 contains bond lengths and bond angles around Na(I) centers.Compound 2 crystallized in the or-thorhombic Pnma space group.The crystal structure of compound 2 consists of a 1D polymeric chain and one uncoordinated BA moiety (Figure 5).The polymeric chain possesses two crystallographically unique Na(I) centers (Na1 and Na2) having a similar coordination environment with minor differences in bond lengths and bond angles.Two neighboring Na(I) centers are bridged by two water molecules, along with one BA and one fum moiety.Na1 centers are hexacoordinated with four bridged water molecules (O1W, O1W ′ , O2W, and O2W ′ ), the O1 atom from the bridged fum, and the O2A atom from the bridged BA molecule.4a).These interactions were further studied theoretically (vide infra).
Figure 5 depicts the molecular structure of compound 2. Tables S3 and S4 contains bond lengths and bond angles around Na(I) centers.Compound 2 crystallized in the orthorhombic Pnma space group.The crystal structure of compound 2 consists of a 1D polymeric chain and one uncoordinated BA moiety (Figure 5).The polymeric chain possesses two crystallographically unique Na(I) centers (Na1 and Na2) having a similar coordination environment with minor differences in bond lengths and bond angles.Two neighboring Na(I) centers are bridged by two water molecules, along with one BA and one fum moiety.Na1 centers are hexacoordinated with four bridged water molecules (O1W, O1W', However, Na2 centers are also hexacoordinated with four bridged water molecules (O1W, O1W ′ , O2W, and O2W ′ ), the O8 atom from bridged fum, and the O3A atom from the bridged BA molecule.The coordination geometry around each Na1 center is distorted octahedron, where the axial sites are filled up by O1 and O2A, while equatorial sites are filled by the four bridged water molecules.The O1W, O1W ′ , O2W, and O2W ′ atoms deviate from the mean equatorial plane with a rms deviation of 0.0304 Å.Similarly, for Na2 centers, axial sites are filled by O8 and O3A, whereas the equatorial positions are filled by four bridged water molecules.The structural properties such as bond lengths and bond angles of the compound are found to be slightly different from those of the previously reported compound (Tables S3 and S4).However, Na2 centers are also hexacoordinated with four bridged water molecules (O1W, O1W´, O2W, and O2W´), the O8 atom from bridged fum, and the O3A atom from the bridged BA molecule.The coordination geometry around each Na1 center is distorted octahedron, where the axial sites are filled up by O1 and O2A, while equatorial sites are filled by the four bridged water molecules.The O1W, O1W´, O2W, and O2W´ atoms deviate from the mean equatorial plane with a rms deviation of 0.0304 Å.Similarly, for Na2 centers, axial sites are filled by O8 and O3A, whereas the equatorial positions are filled by four bridged water molecules.The structural properties such as bond lengths and bond angles of the compound are found to be slightly different from those of the previously reported compound (Tables S3 and S4).  6).The H-bonded ring motif formed in compound 2 is represented by Etter's graph set notation, i.e.,  8 [53].These  8 synthons were further studied theoretically (vide infra).6).The H-bonded ring motif formed in compound 2 is represented by Etter's graph set notation, i.e., R 2 2 (8) [53].These R 2 2 (8) synthons were further studied the- oretically (vide infra).However, Na2 centers are also hexacoordinated with four bridged water molecules (O1W, O1W´, O2W, and O2W´), the O8 atom from bridged fum, and the O3A atom from the bridged BA molecule.The coordination geometry around each Na1 center is distorted octahedron, where the axial sites are filled up by O1 and O2A, while equatorial sites are filled by the four bridged water molecules.The O1W, O1W´, O2W, and O2W´ atoms deviate from the mean equatorial plane with a rms deviation of 0.0304 Å.Similarly, for Na2 centers, axial sites are filled by O8 and O3A, whereas the equatorial positions are filled by four bridged water molecules.The structural properties such as bond lengths and bond angles of the compound are found to be slightly different from those of the previously reported compound (Tables S3 and S4).  6).The H-bonded ring motif formed in compound 2 is represented by Etter's graph set notation, i.e.,  8 [53].These  8 synthons were further studied theoretically (vide infra).

FT-IR Spectroscopy
The FT-IR spectra of compounds 1 and 2 (KBr phase) were recorded in the region 4000-500 cm −1 (Figure 8).The comparatively broad absorption peaks in both compounds at around 3401 and 3447 cm −1 can be attributed to O-H stretching vibrations of water molecules [54,55].FT-IR spectra exhibited peaks due to ρ r (H 2 O) (712 cm −1 ) and ρ w (H 2 O) (645 cm −1 ), which indicates the presence of coordinated water molecules [55].For 1, strong absorption bands at 1601 and 1410 cm −1 are due to the asymmetric and symmetric stretching vibrations of the carboxylate moieties of adp [56].Peaks at 2963 and 2876 cm −1 in 1 are due to the asymmetric and symmetric C-H stretching vibrations of-CH 2 moieties of adp [57,58].Peaks for C-C stretching of the adpcan be observed at 1225 (asymmetric) and 1090 (symmetric) cm −1 in 1 [59].∆ν = ν assym − ν sym of fum (greater than 200 cm −1 ) can be attributed to the monodentate coordination of the carboxylate groups to the Na(I) centers in compound 2 [60].The medium-intensity peaks at 812 and 795 cm −1 in compound 2 are due to the OCO bending vibrations of fum [60].The sharp peak at 1710 cm −1 in 1 indicates that the carboxylate group of adp does not undergo deprotonation, whereas its absence in 2 supports the deprotonation of carboxylate moieties [61].

Theoretical Study
The theoretical study was devoted to the analysis of the H-bonding interactions observed involving boric acid, both as a donor and as an acceptor, that are relevant to the stability of the solid state of the compounds.The polymeric nature of the complexes complicated the theoretical analysis.Therefore, we used finite models of the compounds and took advantage of the QTAIM method that allows the quantification of the H-bonds using the potential energy density values at the bond critical points (CPs).To do so, the Vr values at the bond critical points that characterize each synthon and the equation E = ½Vr were used.As a representative fragment of compound 1, we used the model represented in Figure 10a, composed of a central Na atom coordinated to four water molecules and two monodentate boric acids and two sets of H-bridged adipate dimers.Such a model included the most relevant H-bonds observed in compound 1.The QTAIM analysis combined with the NCI plot analysis is shown in Figure 10a, where each H-bond is characterized by a bond critical point (CP, red sphere) and a bond path connecting the H-atoms to the Oatoms.Moreover, green (weak) and blue (strong) RDG isosurfaces also characterize the H-bonds.One important synthon corresponds to the supramolecular R 2 2 (8) ring, where the BA forms two strong H-bonds with one fum.The formation energy of this synthon is −11.7 kcal/mol due the contribution of both OH•••OH-bonds, where the boric acid acts as a double H-bond donor.The equatorial water molecules participate in two H-bonds, one intramolecular with the BA and the other one intermolecular with the adp.The intermolecular one is stronger (−4.6 kcal/mol), likely due to the anionic nature of the H-bond acceptor.
bonds.One important synthon corresponds to the supramolecular  8 ring, where the BA forms two strong H-bonds with one fum.The formation energy of this synthon is -11.7 kcal/mol due the contribution of both OH•••OH-bonds, where the boric acid acts as a double H-bond donor.The equatorial water molecules participate in two H-bonds, one intramolecular with the BA and the other one intermolecular with the adp.The intermolecular one is stronger (-4.6 kcal/mol), likely due to the anionic nature of the H-bond acceptor.
The oligomeric model used for compound 2 is shown in Figure 10b, composed of a total of six hexacoordinated sodium atoms, three coordinated BAs, two free BAs, and three bidentate fum ligands.It is interesting to highlight the formation of three different  8 synthons in the solid state, which have very large interaction energies.One of the synthons is generated by the interaction of the coordinated and non-coordinated BAs, with a formation energy of -17.8 kcal/mol.The other two  8 synthons correspond to the interaction of the non-coordinated and coordinated BAs with the fumarate ligands.Both synthons exhibit very strong formation energies due to the anionic nature of the Hbond donor and the strong acidity of the H-bond donor atoms.In fact, the strongest synthon (-25.4 kcal/mol) corresponds to the coordinated BA, where the acidity of these OH groups is enhanced by the coordination to the sodium cation.The oligomeric model used for compound 2 is shown in Figure 10b, composed of a total of six hexacoordinated sodium atoms, three coordinated BAs, two free BAs, and three bidentate fum ligands.It is interesting to highlight the formation of three different R 2 2 (8) synthons in the solid state, which have very large interaction energies.One of the synthons is generated by the interaction of the coordinated and non-coordinated BAs, with a formation energy of −17.8 kcal/mol.The other two R 2 2 (8) synthons correspond to the interaction of the non-coordinated and coordinated BAs with the fumarate ligands.Both synthons exhibit very strong formation energies due to the anionic nature of the H-bond donor and the strong acidity of the H-bond donor atoms.In fact, the strongest synthon (−25.4 kcal/mol) corresponds to the coordinated BA, where the acidity of these OH groups is enhanced by the coordination to the sodium cation.

Conclusions
Two Na(I) polymeric compounds were synthesized and characterized using singlecrystal X-ray diffraction, FT-IR, and TG analyses.Compound 1 comprises two polymeric chains: one water-bridged polymeric Na(I) chain and another chain formed by adp molecules with bridging hydrogen atoms.Compound 2 contains a polymeric Na(I) chain bridged by BA and fum moieties.The coordination environment around the Na(I) atoms in both polymers is octahedral.Unconventional supramolecular contacts, namely, C-H•••H-C and parallel CO•••CO interactions, stabilize the layered assembly of compound 1.Interesting dual enclathration of BA molecules within the supramolecular hosts formed by O-H•••O and C-H•••H-C interactions stabilizes the crystal structure of compound 2. The structure-directing H-bonded noncovalent interactions in the crystal structures were further studied theoretically using the combined QTAIM/NCI plot method, and the energies were estimated using the V r energy predictor.It is demonstrated that the formation of a strong structure directing H-bonded R 2 2 (8) synthons in the compounds is relevant for the layered assemblies of the compounds.
1D polymeric chain of compound 1 consisting of the Na(I) centers is stabilized by noncovalent intramolecular O-H•••O hydrogen-bonding interactions (Figure S1 see Supplementary materials).The O4B atoms of the coordinated boric acid molecules are involved in O-H•••O hydrogen-bonding interactions with the bridged water molecule O1W, with O1W-H1WB•••O4B having a distance of 2.09 Å.The 1D polymeric chains of the compound 1 also propagate along the ab plane to stabilize the layered assembly aided by CH•••HC and parallel CO•••CO interactions (Figure S2).H atoms (H4AA, H4AB, H5AA, and H5AB) of the adp molecules are involved in CH•••HC bonding interactions, with H4AA•••H4AB and H5AA•••H5AB separations of 2.40 and 2.34 Å respectively.There are unusual parallel CO•••CO interactions among the carbonyl groups of adp molecules having a Cg1(defined by centroid of C2A and O1A)•••Cg2 (defined by centroid of C2A and O1A)separation of 3.77 Å.The 1D polymeric chains of Na(I) centers of the compound propagate along the crystallographic ab plane and form the layered assembly stabilized by O-H•••O hydrogenbonding interactions (Figure 3).O-H•••O interactions are observed between O2B and O3B atoms of coordinated boric acid molecules (O2B-H2B•••O3B = 1.95 Å).

Figure 2 .
Figure 2. Molecular structure of the polymeric complex 1.The 1D polymeric chains of Na(I) centers of the compound propagate along the crystallographic ab plane and form the layered assembly stabilized by O-H•••O hydrogenbonding interactions (Figure 3).O-H•••O interactions are observed between O2B and O3B atoms of coordinated boric acid molecules (O2B-H2B•••O3B = 1.95 Å).

Figure 3 .
Figure 3. Layered assembly of compound 1 involving the polymeric chains of Na(I) centers assisted by O-H•••O hydrogen-bonding interactions along the crystallographic ab plane.Both the polymeric chains of adp moieties and Na(I) centers are interconnected along the bc plane to stabilize the layered assembly (Figure 4b) aided by C-H•••O and O-H•••O interactions.The -CH (C4AH4A) moiety of adp is involved in C-H•••O hydrogen-bonding interactions with O4B atom of coordinated BA of the Na(I) centers, having a C4A-H4A•••O4B distance of 2.74 Å.The supramolecular ring motif formed is represented using Etter's graph set notation, i.e.,  8 [53].

Figure 3 .
Figure 3. Layered assembly of compound 1 involving the polymeric chains of Na(I) centers assisted by O-H•••O hydrogen-bonding interactions along the crystallographic ab plane.Both the polymeric chains of adp moieties and Na(I) centers are interconnected along the bc plane to stabilize the layered assembly (Figure 4b) aided by C-H•••O and O-H•••O interactions.The -CH (C4AH4A) moiety of adp is involved in C-H•••O hydrogen-bonding interactions with O4B atom of coordinated BA of the Na(I) centers, having a C4A-H4A•••O4B distance of 2.74 Å.The supramolecular ring motif formed is represented using Etter's graph set notation, i.e.,  8 [53].

Figure 3 .
Figure 3. Layered assembly of compound 1 involving the polymeric chains of Na(I) centers assisted by O-H•••O hydrogen-bonding interactions along the crystallographic ab plane.Both the polymeric chains of adp moieties and Na(I) centers are interconnected along the bc plane to stabilize the layered assembly (Figure 4b) aided by C-H•••O and O-H•••O interactions.The -CH (C4AH4A) moiety of adp is involved in C-H•••O hydrogen-bonding interactions with O4B atom of coordinated BA of the Na(I) centers, having a C4A-H4A•••O4B distance of 2.74 Å.The supramolecular ring motif formed is represented using Etter's graph set notation, i.e., R 2 2 (8) [53].Moreover, the O1A and O3A atoms of adp moieties are involved in O-H•••O hydrogenbonding interactions with coordinated BA moieties of the Na(I) centers, having O3B-H3B••• O1A and O4B-H4B•••O3A distances of 1.89 and 2.06 Å, respectively (Figure4a).These interactions were further studied theoretically (vide infra).Figure5depicts the molecular structure of compound 2. Tables S3 and S4 contains bond lengths and bond angles around Na(I) centers.Compound 2 crystallized in the or-

Figure 4 .
Figure 4. (a) Partial view of the layered assembly of compound 1 stabilized by O-H•••O hydrogenbonding interactions.(b) Layered assembly of compound 1 involving both the polymeric chains of adp and Na(I) centers along the crystallographic bc plane.Moreover, the O1A and O3A atoms of adp moieties are involved in O-H•••O hydrogen-bonding interactions with coordinated BA moieties of the Na(I) centers, having O3B-H3B•••O1A and O4B-H4B•••O3A distances of 1.89 and 2.06 Å, respectively (Figure4a).These interactions were further studied theoretically (vide infra).Figure5depicts the molecular structure of compound 2. Tables S3 and S4 contains bond lengths and bond angles around Na(I) centers.Compound 2 crystallized in the orthorhombic Pnma space group.The crystal structure of compound 2 consists of a 1D polymeric chain and one uncoordinated BA moiety (Figure5).The polymeric chain possesses two crystallographically unique Na(I) centers (Na1 and Na2) having a similar coordination environment with minor differences in bond lengths and bond angles.Two neighboring Na(I) centers are bridged by two water molecules, along with one BA and one fum moiety.Na1 centers are hexacoordinated with four bridged water molecules (O1W, O1W',

Figure 4 .
Figure 4. (a) Partial view of the layered assembly of compound 1 stabilized by O-H•••O hydrogenbonding interactions.(b) Layered assembly of compound 1 involving both the polymeric chains of adp and Na(I) centers along the crystallographic bc plane.

Figure 6 .
Figure 6.The 1D polymeric chain of compound 2 involving intramolecular and intermolecular O-H•••O hydrogen-bonding interactions.Unusual dual enclathration of lattice boric acid moieties within the supramolecular host cavity aided by O-H•••O and C-H•••C interactions (Figure 7a) stabilize the layered assembly of the compound.The O7 atom of bridging fum and the O2W molecule

Figure 6 .
Figure 6.The 1D polymeric chain of compound 2 involving intramolecular and intermolecular O-H•••O hydrogen-bonding interactions.Unusual dual enclathration of lattice boric acid moieties within the supramolecular host cavity aided by O-H•••O and C-H•••C interactions (Figure 7a) stabilize the layered assembly of the compound.The O7 atom of bridging fum and the O2W molecule

Figure 7 .
Figure 7. (a) Dual enclathration of lattice BA molecules in the supramolecular host cavity formed of 2. (b) The 2D architecture of 2 along the crystallographic ac plane aided by dual enclathration of lattice BA molecules within the supramolecular host cavity.

Figure 7 .
Figure 7. (a) Dual enclathration of lattice BA molecules in the supramolecular host cavity formed of 2. (b) The 2D architecture of 2 along the crystallographic ac plane aided by dual enclathration of lattice BA molecules within the supramolecular host cavity.

Table 1 .
Crystallographic data and structure refinement details for compounds 1 and 2.