Synthesis of an eight-membered 2,2,4,6,6,8-hexaphenyl-1,3,5,7,2,6,4,8-tetraoxadisiladiborocane and its reaction with 4,4-azo-pyridine leading to ring contraction to give a dimer and hydrogen bonded macrocyclic siloxane-azo-pyridine European Journal of Chemistry 16 (1) (2025) 37-45 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2025 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.16.1.37-45.2608 European Journal of Chemistry View Journal Online View Article Online Synthesis of an eight-membered 2,2,4,6,6,8-hexaphenyl-1,3,5,7,2,6,4,8- tetraoxadisiladiborocane and its reaction with 4,4-azo-pyridine leading to ring contraction to give a dimer and hydrogen bonded macrocyclic siloxane-azo- pyridine Okpara Sergeant Bull 1,*, Chioma Don-Lawson 1, and Ahamefula Anslem Ahuchaogu 2 1 Department of Chemistry, Rivers State University, Nkpolu-Oroworukwo, Port Harcourt, Private Mail Bag 5080, Nigeria 2 Department of Pure and Industrial Chemistry, Abia State University, Uturu 441103, Abia, Nigeria * Corresponding author at: Department of Chemistry, Rivers State University, Nkpolu-Oroworukwo, Port Harcourt, Private Mail Bag 5080, Nigeria. e-mail: bull.okpara@ust.edu.ng (O.S. Bull). 10.5155/eurjchem.16.1.37-45.2608 Received: 20 October 2024 Received in revised form: 8 February 2025 Accepted: 18 February 2025 Published online: 31 March 2025 Printed: 31 March 2025 We hereby report the syntheses and characterization of a new dimer of azopyridine connected through the six-membered B-N dative-bonded-adduct Ph8B4Si2O6·L (4) and a hydrogen-bond-induced macrocyclic product 4(Ph2Si(OH)2)·3(C10H8N4) (5). The products were obtained after an eight-membered 2,2,4,6,6,8-hexaphenyl-1,3,5,7,2,6,4,8-tetraoxa disiladiborocane (Ph6B2Si2O4) (3), which is abundant in the literature, was successfully synthesized and characterized by standard analytical and spectroscopic methods such as single-crystal XRD, melting point, nuclear magnetic resonance and Fourier transform infrared spectroscopy. Subsequently, compound 3 and 4,4-azopyridine (L) were reacted in a mixture of diethyl ether and petroleum ether solvents at reflux. This reaction caused a contraction of the eight-membered compound 3 to give two products - a dimer compound 4 (Ph8B4Si2O6·L), and a macrocyclic product 4(Ph2Si(OH)2)·3(C10H8N4) (5). These two products have been characterized by single-crystal XRD, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and melting point. Single crystal X-ray diffraction studies reveal that the dimer compound 4 compound crystalized in the monoclinic crystal system with a centrosymmetric space group of P21/c, a = 11.0879(4) Å, b = 14.3707(4) Å, c = 16.2697(5) Å, β = 98.759(3)°, V = 2562.20(13) Å3, Z = 2. On the other hand, the macrocyclic product 4(Ph2Si(OH)2)·3(C10H8N4) (5) is orange blocky needles that crystallized in the triclinic crystal system with a centrosymmetric space group of P-1, a = 12.2352(3) Å, b = 15.3274(6) Å, c = 20.0271(6) Å, α = 89.879(3)°, β = 89.988(2)° γ = 78.298(3)°, V = 3677.7(2) Å3, Z = 2. Furthermore, compounds 4 and 5 exhibit various noncovalent interactions in crystal packing, such as intermolecular and intramolecular π-π as well as hydrogen bonding. This study demonstrates the potential for making novel materials via the combination of cyclodiboradisiloxane (a Lewis acid) and nitrogen-containing ligand (a Lewis base). 4,4-Azo-pyridine Diphenylsilanediol Phenylboronic acid Cyclodiborasiloxane B-N dative-bonded-dimer Macrocyclic siloxane-azo-pyridine Cite this: Eur. J. Chem. 2025, 16(1), 37-45 Journal website: www.eurjchem.com 1. Introduction For a long time, cyclodiboradisiloxanes, and their deriva- tives as a class of organoborasilicon compounds, have been the focus of a large number of studies due to their exceptional structural architecture [1,2], magnetic properties [3], electronic properties [4], optical properties [5], quasiaromatic characters [2] as well as their aptitude for the formation of extended π-π intramolecular and intermolecular interactions [6]. These group of compounds consists mainly of alkyl Si-O-B and O-B-O ring systems for which the boron centers (if tricoordinated) are further ligated with Lewis bases such as pyridines, leading to the formation of a B-N dative bond, which imparts remarkable stability and reactivity [2,7]. The presence of silicon and oxygen atoms within cyclodiboradisiloxane bestows the framework unusual high elasticity and plasticity when subjected to sudden and slow stress [2,8]. Boron-nitrogen adducts, such as those formed between cyclodiboradisiloxanes and nitrogen- containing ligands, have shown great promise in various fields, such as conductive polymers for advanced energy devices, catalysis, carbon capture, gas separation and adsorption, lightweight, high-strength materials for application in space- craft, pharmaceuticals, and drug delivery [9]. The ability to form stable, covalent bonds between boron and nitrogen atoms enables the creation of novel materials with tailored properties. Furthermore, polymers, in particular, have revolutionized modern technology, finding applications in everything from packaging materials to advanced electronics [9-11]. The development of novel polymers with unique properties, such as conductivity [5], luminescence [12], or response to stimulation [13,14], is an active area of research [15]. Incorporation of cyclodiboradisiloxanes and boron-nitrogen adducts into polymer backbones or side chains offers a promising route to create materials with improved performance and functionality [16]. Regardless of the functions and uses of this borasiloxane material, as well as their promising future prospects, only a few ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.16.1.37-45.2608 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.16.1.37-45.2608 mailto:bull.okpara@ust.edu.ng http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.16.1.37-45.2608&domain=pdf&date_stamp=2025-03-31 38 Bull et al. / European Journal of Chemistry 16 (1) (2025) 37-45 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.1.37-45.2608 Scheme 1. Synthesis of 2,2,4,6,6,8-hexaphenyl-1,3,5,7,2,6,4,8-tetraoxadisiladiborocane (3), six-membered cyclodiborasiloxane and hydrogen-bonded macrocyclic siloxane-azopyridine. of these materials are available in the literature [2]. This dearth of literature and materials could be as a result of a handful of commercially available silanols, difficulty in structural modification of available materials as well as problems of stability. The aromatic and potential quasi-aromatic character, and the ability to form extended π-π intramolecular and intermolecular interactions of a ring system are governed by the general formula BnSimOn+m [2,17]. This implies that rings of general formula, BnSimOn+m will have 2(n + m) π-electrons available for delocalization from the oxygen lone pairs [2]. If n + m = 3, the Hückel principle of 6 π-electrons is satisfied, while if n + m = 4, an anti-aromatic 8 π-electron count results [2]. Furthermore, the ring systems (B-O-Si) and (Si-O-Si) have been used as molecular building blocks in the construction of metal- organic frameworks (MOFs) [3-9], covalent organic frame- works (COFs) [3,10,11] and other supramolecular compound such as silsesquioxanes [10]. The methods for the preparation of these materials are discussed in details in the literature [2- 4,18-21]. However, the method used in this study is similar to that described in the literature [2,7], for which molecular sieves were used for the removal of water to obtain crude compound 3. Compound 3 (a Lewis acid) was then ligated with 1,2-di (pyridin-4-yl) ethane, resulting in the formation of the aforementioned 1D polymer following a literature procedure [2]. Therefore, the main purpose of the study is the synthesis of 2, 2, 4, 6, 6, 8-hexaphenyl-1, 3, 5, 7, 2, 6, 4, 8-tetraoxadisiladi- borocane (3), and its reaction with 4,4-azopyridine (L) leading to a ring contraction to give a dimer and hydrogen-bonded macrocyclic siloxane-azo-pyridine as shown in Scheme 1. 2. Experimental 2.1. Chemicals and reagents All reactions were carried out under an inert atmosphere of dry nitrogen. All chemicals, reagents, and solvents were purchased from Sigma-Aldrich or Alfa-Aesar and used as received unless otherwise stated. Molecular sieves (1.6 mm rods and 0.4 nm pores) were preheated to dryness in the oven at 120 °C for two weeks prior to use. 2.2. Instrumentation 1H, 13C{1H}, 11B{1H} and 29Si{1H} NMR spectra were recorded on Bruker Avance III HD 400 MHz or 500 MHz spectrometers in CDCl3 solvent unless otherwise stated. The chemical shifts (δ) for 1H and 13C{1H}, 29Si{1H}, and 11B{1H}, are quoted in ppm with reference to Me4Si and BF3OEt2, respectively. The coupling constants are reported in Hz. Infrared spectra were obtained on a Perkin Elmer Spectrum 100 FTIR Spectrometer operating in ATR mode. The melting points were obtained using the Stanford Research Systems MPA100 (CE LABELED) automatic digital melting point apparatus 03012-90. Elemental analyzes were performed using a Thermo Quest CE Instruments Model EA/110 CHNS-O elemental analyzer. The single crystal diffraction (SC-XRD) measurement was performed on a Bruker D-QUEST diffracto- meter. The intensity data were collected using graphite monochromated with λ = 0.71073 Å. The structure was solved by the direction method and refined by full matrix least squares against F2 for all data using SHELXTL-97 program. The carbon and hydrogen atoms were positioned geometrically and constrained to ride on their parent atoms with Uiso(H) = 1.2Ueq(C). The hydrogen atoms on the nitrogen were located in the difference Fourier map and refined freely using SHELXL instruction ′DFIX 0.87 0.01. The MS instrument is the MALDI- TOF (Matrix-Assisted Laser Desorption/ Ionization Time-of- Flight. Bull et al. / European Journal of Chemistry 16 (1) (2025) 37-45 39 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.1.37-45.2608 Figure 1. An ORTEP view of compound 4 with atom numbering. 2.3. Synthesis 2.3.1. Synthesis of compound 3 (Ph6B2Si2O4) In a round bottom flask equipped with a magnetic stirrer bar, diphenylsilanediol (1) 1.082 g, (5.0 mmol) was mixed with 0.609 g (5.0 mmol) of phenylboronic acid (2) in dry toluene (50 mL) and 0.5 g of molecular sieves. The mixture was refluxed under N2 for 20 h. Thereafter, the round bottom flask and its contents were cooled to room temperature. The mixture was filtered and the filtrate collected. The molecular sieves were washed with dry toluene (3×25 mL). The filtrates were combined and concentrated under reduced pressure, and the solid residue was recrystallized from diethyl ether and petroleum ether (3:1 ratio) to give compound 3 (Scheme 1). 2,2,4,6,6,8-Hexaphenyl-1,3,5,7,2,6,4,8-tetraoxadisiladiborocane (3): Color: White. Yield: 86%. M.p.: 162-163 °C. 1H NMR (500 MHz, CDCl3, δ, ppm): 7.31-7.54 (m, 18H, m,p-C6H5), 7.73-7.75 (m, 8H o-C6H5Si), 8.08-8.10 (m, 4H, o-C6H5B). 13C NMR (125 MHz, CDCl3, δ, ppm): 127.93, 128.06, 130.60, 131.74, 133.40, 134.12, 135.65 (C6H5Si, C6H5B). 11B NMR (160 MHz, CDCl3, δ, ppm): 25.69. 29Si{1H} NMR (99 MHz, CDCl3, δ, ppm): -45.00. MS (70 eV, EI, m/z): 604 (M+), 527 (M-Ph)+, 423 (M-Ph-PhBO)+, 406 (M-Ph2SiO)+. FT-IR (ATR, ν, cm-1): 3023 (C-H aromatic), 1349 (B-O), 1307 (Si-C str.), 1071 (Si-O str.) 2.3.2. Synthesis of compound 4 [Ph8B4Si2O6]·L In a round bottom flask, compound 3 (0.25 g, 0.415 mmol) was dissolved in ether (20 mL) and then stirred with a magnetic stirrer bar. In another round bottom flask, 4,4'-azopyridine (L) (0.076 g, 0.415 mmol) was dissolved in ether (20 mL) and stirred. The solution of compound 3 was added to the L solution while stirring. The reaction mixture was stirred for 24 h during which time an orange-brown precipitate formed. The removal of solvents via filtration yielded an orange-brown powder as shown in Scheme 1. Recrystallization of the powder from CH2Cl2:ether (1:1, v:v) gave compound 4 as orange crystals after 24 h. Compound 4: Color: Orange. Yield: 80%. M.p.: 194-195 °C. 1H NMR (500 MHz, CDCl3, δ, ppm): 7.27-7.36 (m, 8H, m-C6H5Si), 7.49-7.55 (m, 4H, p-C6H5Si), 7.68-7.74 (m, 8H, o-C6H5Si), 7.76- 7.78 (m, 4H, p-C6H5B), 7.84-7.87 (m, 8H, m-C6H5B), 8.04-8.10 (m, 8H, o-C6H5B), 8.11-8.18 (m, 4H, m-C5H4N), 8.94-8.97 (m, 4H, o-C5H4N). 13C NMR (125 MHz, CDCl3, δ, ppm): 156.95, 150.13, 135.57, 135.02, 134.37, 134.08, 133.80, 133.40, 131.64, 130.53, 129.98, 128. 06, 128.00, 127.87, 127.62, 116.90. 11B NMR (160 MHz, CDCl3, δ, ppm): 29.52, 22.36. 29Si{1H} NMR (99 MHz, CDCl3, δ, ppm): -45.04. FT-IR (KBr, ν, cm-1): 3071 (C-H aromatic), 3004 (C-H), 1624 (C=C), 1436 (B-O), 1340 (C-N aromatic), 1289 (Si-C str.), 1063 (Si-O). Anal. calcd. for C58H48B4N4O6Si2: C, 69.91, H, 4.86, N, 5.62. Found: C, 69.84, H, 4.94; N, 5.70%. 2.3.3. Synthesis of compound 5 [4(C12H12O2Si)·3(C10H8N4)] In a round bottom flask, compound 3 (0.25 g, 0.415 mmol) was dissolved in ether:petroleum ether (2:1, v:v) (20 mL) and then stirred with a magnetic stirrer bar. In another round bottom flask, 4,4'-azopyridine (L) (0.076 g, 0.415 mmol) was dissolved in ether:petroleum ether (2:1, v:v) (20 mL) and stirred. The solution of compound 3 was added to the 4,4'- azopyridine solution while stirring. The reaction mixture was stirred for 24 h where an orange-brown precipitate formed. The removal of solvents via filtration yielded an orange-brown powder. Recrystallization of the powder from CH2Cl2:ether (1:1, v:v) gave compound 5 as orange-brown crystals after 24 h. Compound 5: Colour: Orange-brown. Yield: 16%. M.p.: 190-193 °C. FT-IR (KBr, ν, cm-1): 3071 (C-H aromatic), 3004 (C-H), 1624 (C=C), 1436 (B-O), 1340 (C-N aromatic), 1289 (Si-C str.), 1063 (Si-O). Anal. calcd. for C78H72N12O8Si4: C, 66.08, H, 5.12, N, 11.85. Found: C, 66.47, H, 4.69; N, 11.83%. 3. Results and discussion 3.1. Compound 4 [Ph8B4Si2O6]·L The 11B{1H} NMR spectrum of compound 4 showed two singlets at δ 29.52 and 22.36 ppm, while the 29Si{1H} NMR of compound 4 showed a singlet at δ -45.04 ppm. The crystal structure confirms compound 4 as a dimer instead of a 1-D polymer-like compounds in the literature [2,7]. Furthermore, in the reaction leading to the formation of compound 4, the eight-membered ring of compound 3 has contracted to a six- membered ring (Ph2B2Ph2SiO3) together with Ph2Si(OH)2. The Ph2B2Ph2SiO3 then reacted with the linker (L) to form compound 4, while Ph2Si(OH)2 interacted with the linker (L) via hydrogen bonding to give compound 5 discussed in detail below. The ORTEP diagram with atom numbering shown in Figure 1 shows that the B1 and B3 atoms are tetracordinated and tricoordinated, respectively. The linker (L) bridges the two B2SiO3 rings via a dative bond on the two B1 atoms. The B1-O2 and B1-O6 distances at the tetragonal boron atoms (B1) in compound 4 are 1.451(3) and 1.446(3) Å, respectively. The B3-O2 and B3-O4 bond lengths at the trigonal boron atoms (B3) are 1.346(3) and 1.373(3) Å, respectively. Therefore, the lengths of the B-O bonds associated with tetrahedrally coordinated B1 are longer than those of the tricoordinate B3 in compound 4, consistent with stronger Bπ···Oπ interactions with O atoms bound to Bsp2-O than Bsp3-O. The trigonally bonded boron in the B-O distance in compound 4 is comparable to the tricoordinated B-O distance of 1.374(7) Å, reported for the Ph5Si2BO3 ring [17], as well as to other tricoordinated B-O distances in other Si2B2O4 rings, which ranges from 1.36-1.39 Å [21-23]. However, the values reported here are comparable to other B-O distances for tetrahedrally coordinated B in compounds such as N(CH2CH2O)B (1.43(1) Å) 40 Bull et al. / European Journal of Chemistry 16 (1) (2025) 37-45 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.1.37-45.2608 Table 1. Crystal data and structure refinement for compound 4. Empirical formula C58H48B4N4O6Si2 Formula weight (g/mol) 996.42 Temperature (K) 173(2) Crystal system Monoclinic Space group P21/c a, (Å) 11.0879(4) b, (Å) 14.3707(4) c, (Å) 16.2697(5) α (°) 90 β (°) 98.759(3) γ (°) 90 Volume (Å3) 2562.20(13) Z 2 ρcalc (g/cm3) 1.292 μ (mm-1) 0.126 F(000) 1040.0 Crystal size (mm3) 0.46 × 0.42 × 0.04 Radiation MoKα (λ = 0.71073) 2Θ range for data collection (°) 5.066 to 56.49 Index ranges -13 ≤ h ≤ 9, -16 ≤ k ≤ 18, -13 ≤ l ≤ 21 Reflections collected 8564 Independent reflections 5118 [Rsigma = 0.0569] Data/restraints/parameters 5118/0/334 Goodness-of-fit on F2 1.049 Final R indexes [I≥2σ (I)] R1 = 0.0570, wR2 = 0.1394 Final R indexes [all data] R1 = 0.0789, wR2 = 0.1559 Largest diff. peak/hole (e.Å-3) 0.35/-0.55 Table 2. Selected bond lengths for compound 4 *. Atom Atom Length (Å) Atom Atom Length (Å) B1 O2 1.451(3) Si5 C32 1.868(3) B1 O6 1.446(3) N7 C8 1.339(3) B1 N7 1.670(3) N7 C12 1.338(3) B1 C14 1.614(4) C8 C9 1.381(3) O2 B3 1.346(3) C9 C10 1.376(3) B3 O4 1.373(3) C10 C11 1.387(3) B3 C20 1.569(3) C10 N13 1.432(3) O4 Si5 1.6573(17) C11 C12 1.371(3) Si5 O6 1.6116(16) N13 N13 1 1.238(4) Si5 C26 1.845(2) C14 C15 1.382(3) * Symmetry code: 1 1-x, -y, -z. Table 3. Selected bond angles for compound 4 *. Atom Atom Atom Angle (°) Atom Atom Atom Angle (°) O2 B1 N7 103.80(18) C26 Si5 C32 110.32(11) O2 B1 C14 111.44(19) B1 O6 Si5 123.75(15) O6 B1 O2 115.7(2) C8 N7 B1 119.67(19) O6 B1 N7 105.08(17) C12 N7 B1 121.12(18) O6 B1 C14 114.5(2) C12 N7 C8 119.2(2) C14 B1 N7 104.82(17) N7 C8 C9 121.7(2) B3 O2 B1 127.08(19) C10 C9 C8 118.8(2) O2 B3 O4 121.7(2) C9 C10 C11 119.6(2) O2 B3 C20 118.0(2) C9 C10 N13 116.9(2) O4 B3 C20 120.2(2) C11 C10 N13 123.6(2) B3 O4 Si5 122.40(15) C12 C11 C10 118.3(2) O4 Si5 C26 106.55(10) N7 C12 C11 122.4(2) O4 Si5 C32 108.64(10) N13 1 N13 C10 112.9(2) O6 Si5 O4 106.46(9) C15 C14 B1 122.9(2) O6 Si5 C26 113.58(10) C15 C14 C19 117.1(2) O6 Si5 C32 111.02(10) C19 C14 B1 119.9(2) [24], Ph2BOCH2CH2NH2 (1.484(3) Å) [25], and Ph(OSiR2R’) B{OCH2)3N} (1.439(4) Å, and 1.461(3) Å) [26], (R or R’ = Ph or CH3) and [ButSi(OPhBO)3SiBut]·NC5H5 (1.457(18) Å, and 1.469(18) Å) [22] where the B is directly bonded to two O atoms, a phenyl group, and the N atom. The Si-O bond lengths in compound 4 are 1.6573(17) Å (Si5-O4) and 1.6116(16) Å (Si5-O6), which are similar to those found in the literature [2,5,7] and comparable to the bond lengths for Si-O for a four-coordinate Si to two O atoms with a mean value of 1.645 Å [21,22,26]. The shorter Si5-O6 distances associated with compound 4 suggest an increase in electron density in the Si5-O6 bond, which is consistent with the decrease in the B-O electron density. The B1-N7 bond length of compound 4 is 1.670(3) Å which is similar to those found in references [2,7], but a bit longer than those of simple borosiloxane such as Ph(OSiR2R’)B{OCH2)3N} [26] (R or R’ = Ph or CH3) and [ButSi(OPhBO)3SiBut]·NC5H5 [22] where the B-N distances reported were 1.639 and 1.655 Å, respectively. The two Si-C bond lengths in compound 4 are 1.845(2) Å (Si5-C26) and 1.868(3) Å (Si5-C32) and are similar to those found in the literature [2,7]. The ring angles O2-B1-O6 and O2-B3-O4 are 115.7(2)° and 121.7(2)°, respectively. The angle of the internal ring of compound 4 at the tetrahedral coordinated B (B1) is higher than the expected 109.5° for a tetrahedral geometry but similar to the compounds in the literature [2,7] as well as the observations reported in the literature [22]. However, the ring angle O2-B3-O4 for the three coordinate B (B3) is higher than that of the tetracoordinated boron centre but similar to other compounds in the literature [21,22,27,28]. Similarly, the angle Bull et al. / European Journal of Chemistry 16 (1) (2025) 37-45 41 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.1.37-45.2608 (a) 2.461 Å 2.853 Å 3.527 Å (b) Figure 2. (a) Crystal packing and (b) noncovalent interactions of compound 4. Figure 3. An ORTEP view of compound 5 with atom numbering. of O4-Si5-O6 is 106.46(9)° which is lower than 109.5° for a tetrahedral silicon but is comparable to the values of the literature [29]. The bond angles at Si as well as the Si-C bonds lengths are comparable to those [2,7] as well as other borasiloxane compounds and simple adducts in the literature [21,22,27]. In addition to the covalent and dative bonds found in compound 4, the crystal packing of the compound also shows noncovalent interactions such as C-H···π (2.853 Å), C-H···N (2.461 Å) and π···B3 (3.527 Å) as shown in Figure 2. The crystallographic data of compound 4 are shown in Tables 1-3. 3.2. Compound 5 [4(C12H12O2Si) 3(C10H8N4)] Compound 5 is a combination of L and the other part of the product [Ph2Si(OH2)] from the preparation of compound 4, in which compound 3 contracted into a six-membered ring (Ph2B2Ph2SiO3) and Ph2Si(OH)2 as described above. As the crystals of compounds 4 and 5 have different morphologies and shapes, compound 5 was isolated by hand picking from that of compound 4 but in low yield. The crystal structure of Ph2Si(OH)2 and the linker (L) that gave compound 5 [4[Ph2Si(OH)2]·3(C10H8N4)] is shown in Figure 3. The Ph2Si(OH)2 and the linker (L) interact through hydrogen bonding (H···O and H···N) as shown in Figure 3. 42 Bull et al. / European Journal of Chemistry 16 (1) (2025) 37-45 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.1.37-45.2608 Table 4. Crystal data and structure refinement for compound 5. Empirical formula C78H72N12O8Si4 Formula weight (g/mol) 1417.83 Temperature (K) 173(2) Crystal system Triclinic Space group P-1 a, (Å) 12.2352(3) b, (Å) 15.3274(6) c, (Å) 20.0271(6) α (°) 89.879(3) β (°) 89.988(2) γ (°) 78.298(3) Volume (Å3) 3677.7(2) Z 2 ρcalc (g/cm3) 1.280 μ (mm-1) 0.146 F(000) 1488.0 Crystal size (mm3) 0.64 × 0.27 × 0.13 Radiation MoKα (λ = 0.71073) 2Θ range for data collection (°) 4.886 to 56.208 Index ranges -12 ≤ h ≤ 15, -20 ≤ k ≤ 18, -25 ≤ l ≤ 25 Reflections collected 20569 Independent reflections 20569 [Rsigma = 0.0829] Data/restraints/parameters 20569/649/991 Goodness-of-fit on F2 0.891 Final R indexes [I≥2σ (I)] R1 = 0.0470, wR2 = 0.1013 Final R indexes [all data] R1 = 0.0891, wR2 = 0.1098 Largest diff. peak/hole (e.Å-3) 1.04/-0.50 Table 5. Selected bond lengths for compound 5 *. Atom Atom Length (Å) Atom Atom Length (Å) Si1A O1A 1.6176(18) C23A N26A 1.452(3) Si1A O2A 1.6126(18) N26A N27A 1.205(3) Si1A C1A 1.862(3) N27A C28A 1.465(3) Si1A C7A 1.865(3) C30A N31A 1.329(3) Si1B O1B 1.6314(17) N31A C32A 1.338(3) Si1B O2B 1.6218(17) N20B C21B 1.342(3) Si1B C1B 1.864(2) N20B C25B 1.323(3) Si1B C7B 1.860(3) C23B N26B 1.469(3) Si1C O1C 1.6183(17) N26B N27B 1.201(3) Si1C O2C 1.6169(18) N27B C28B 1.488(3) Si1C C1C 1.861(2) C30B N31B 1.328(3) Si1C C7C 1.858(3) N31B C32B 1.335(3) Si1D O1D 1.6308(16) C43A N46A 1.515(5) Si1D O2D 1.6253(17) N46A N47A 1.113(5) Si1D C1D 1.867(2) N47A C48A 1.423(5) Si1D C7D 1.859(3) N40B C41B 1.323(3) N20A C21A 1.339(3) N40B C45B 1.328(3) N20A C25A 1.322(3) N46B N46B1 1.219(4) * Symmetry code: 1 2-x, 1-y, -z. Table 6. Selected bond angles for compound 5 *. Atom Atom Atom Angle (°) Atom Atom Atom Angle (°) O1A Si1A C1A 105.92(11) C8D C7D Si1D 121.81(18) O1A Si1A C7A 109.47(11) C12D C7D Si1D 121.8(2) O2A Si1A O1A 113.68(10) C25A N20A C21A 116.3(2) O2A Si1A C1A 104.10(10) N20A C21A C22A 123.9(3) O2A Si1A C7A 111.02(10) C22A C23A N26A 126.6(2) C1A Si1A C7A 112.50(11) C24A C23A N26A 114.2(3) C2A C1A Si1A 120.6(2) N20A C25A C24A 124.6(3) C6A C1A Si1A 121.9(2) N27A N26A C23A 112.6(2) C8A C7A Si1A 120.5(2) N26A N27A C28A 112.3(2) C12A C7A Si1A 122.7(2) C29A C28A N27A 115.5(3) O1B Si1B C1B 105.81(10) C33A C28A N27A 125.3(2) O1B Si1B C7B 109.57(10) N31A C30A C29A 124.3(3) O2B Si1B O1B 113.39(9) C30A N31A C32A 116.6(2) O2B Si1B C1B 107.31(10) N31A C32A C33A 123.2(3) O2B Si1B C7B 108.40(10) C25B N20B C21B 116.5(2) C7B Si1B C1B 112.39(11) N20B C21B C22B 123.6(3) C2B C1B Si1B 119.63(19) C22B C23B N26B 127.1(2) C6B C1B Si1B 123.32(19) C24B C23B N26B 113.5(2) C8B C7B Si1B 121.72(18) N20B C25B C24B 124.1(3) C12B C7B Si1B 121.98(19) N27B N26B C23B 110.5(2) O1C Si1C C1C 106.48(10) N26B N27B C28B 110.4(2) O1C Si1C C7C 109.19(10) C29B C28B N27B 114.2(3) O2C Si1C O1C 114.25(10) C33B C28B N27B 125.9(3) O2C Si1C C1C 103.97(10) N31B C30B C29B 124.2(3) O2C Si1C C7C 110.80(10) C30B N31B C32B 116.8(2) C7C Si1C C1C 112.03(11) N31B C32B C33B 123.1(3) C2C C1C Si1C 120.50(18) C42A C43A N46A 115.3(3) C6C C1C Si1C 122.57(19) C44A C43A N46A 124.5(3) C8C C7C Si1C 120.93(19) N47A N46A C43A 110.6(4) Bull et al. / European Journal of Chemistry 16 (1) (2025) 37-45 43 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.1.37-45.2608 Table 6. Continued. Atom Atom Atom Angle (°) Atom Atom Atom Angle (°) C12C C7C Si1C 122.5(2) N46A N47A C48A 112.2(6) O1D Si1D C1D 106.43(9) C49A C48A N47A 108.5(4) O1D Si1D C7D 109.26(10) C53A C48A N47A 131.5(4) O2D Si1D O1D 113.39(9) C41B N40B C45B 117.7(2) O2D Si1D C1D 107.22(10) N40B C41B C42B 124.0(3) O2D Si1D C7D 109.66(10) C42B C43B N46B 114.7(2) C7D Si1D C1D 110.83(11) C44B C43B N46B 125.1(2) C2D C1D Si1D 119.53(18) N40B C45B C44B 122.6(3) C6D C1D Si1D 123.70(18) N46B1 N46B C43B 111.6(3) (a) (b) 2.507 Å 3.330 Å 2.456 Å H22B H44B H22B H33B N25B 2.493 Å N26B N27B N46B (c) Figure 4. (a) Crystal packing of compound 5 and (b) and (c) intramolecular and intermolecular interactions. As can be seen in Figure 3, the H atoms that bond with O atoms in the molecule are H2A···O1B (1.815 Å) and H2A···O1A (1.815 Å), while H1A and H2B hydrogen bond with N31B (H1A···N31B) (1.891 Å) and N20B (H2B···N20B) (1.931 Å), respectively. H1B hydrogen bonds with another molecule at N40B (H1B···N40B) (1.773 Å). Therefore, the three-linker L molecules that bond to the four Ph2Si(OH)2 molecules are parallel to each other. In addition to the hydrogen bonding displayed by compound 5, the crystal packing of the compound also shows other forms of inter- and intra-non-covalent (C- H···N, C-H···O, C-H···π, and π···π) interactions as depicted in Figure 4. The ring angle from O1A-Si1A-O2A and O1B-Si1B-O2B is 113.68° and 113.40°, which are higher than those of compound 4 (106.46(9)°) but comparable to those of the literature [2,7]. Furthermore, individual molecules of compound 5 interact intermolecularly via C-H···N (3.330 Å). 44 Bull et al. / European Journal of Chemistry 16 (1) (2025) 37-45 2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.1.37-45.2608 The sum of all these interactions and the stability of products 4 and 5 as well as the basicity of L may be the reason for the contraction of the compound 3 ring to (Ph2B2Ph2SiO3) and Ph2Si(OH)2, which later reacted with the linker L to give compounds 4 and 5, respectively. Crystallographic data of compound 5 are in Tables 4-6. 4. Conclusions In this article, we report the successful synthesis of an eight- membered 2, 2, 4, 6, 6, 8-hexaphenyl-1, 3, 5, 7, 2, 6, 4, 8-tetraoxa disiladiborocane (Ph6B2Si2O4) (3) (a Lewis acid) and its reaction with 4,4-azo-pyridine (L) (a Lewis base) leading to the contraction of compound 3 to form a six-membered cyclodiborasiloxane dimer (compound 4) and a hydrogen- bonded connected macrocyclic system. Crystal structures of these compounds 4 and 5 were determined using single crystal X-ray diffraction. The dimer shows extensive channels in its packing occupied by solvent molecules. Furthermore, the structure dimer possesses intermolecular and intramolecular π-π interactions as well as hydrogen bonding. Furthermore, compound 5 showed more extensive hydrogen (inter and intra) bonding than the dimer. These two novel compounds have a promising potential to enhance the performance and functionality of borasiloxane backbone materials. Hence, further work is recommended to explore some functions and uses of these unique compounds in areas such as the heterogeneous catalyst in the conversion of waste cooking oil to biodiesel, the adsorption of heavy metals from waste water, etc. [1,3,18,30,31], synthesis of silicon-based dendrimers and cores. Acknowledgements We gratefully acknowledge the financial support given to us by the Nigerian Government through the Petroleum Technology Development Fund (PTDF), the Tertiary Education Trust Fund (TETFUND), and the Rivers State University, Port Harcourt, Nigeria. Supporting information CCDC-2429585 and -2429589 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by e-mailing data_request@ ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033. Disclosure statement Conflict of interest: The authors declare that they have no conflict of interest. Ethical approval: All ethical guidelines have been adhered. Sample availability: Samples of the compounds are available from the author. CRediT authorship contribution statement Conceptualization: Okpara Sergeant Bull; Methodology: Okpara Sergeant Bull; Software: Okpara Sergeant Bull; Validation: Don-Lawson Chioma, Okpara Sergeant Bull, Ahamefula Anslem Ahuchaogu; Formal Analysis: Ahamefula Anslem Ahuchaogu; Investigation: Okpara Sergeant Bull; Resources: Don-Lawson Chioma; Data Curation: Okpara Sergeant Bull; Writing - Original Draft: Okpara Sergeant Bull Writing - Review and Editing: Okpara Sergeant Bull, Don-Lawson Chioma; Visualization: Don-Lawson Chioma; Funding acquisition: Don-Lawson Chioma, Ahamefula Anslem Ahuchaogu; Supervision: Don-Lawson Chiom; Project Administration: Okpara Sergeant Bull. ORCID and Email Okpara Sergeant Bull bull.okpara@ust.edu.ng https://orcid.org/0000-0002-5810-1483 Chioma Don-Lawson chioma.don-lawson@ust.edu.ng https://orcid.org/0009-0005-2593-7873 Ahamefula Anslem Ahuchaogu ahuchaogu.aa@abiastateuniversity.edu.ng https://orcid.org/0000-0002-6412-7487 References [1]. Bull, O. 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Synthesis, properties, and the ring-ring transformation reactions of cyclic siloxanes incorporating skeletal boron atoms: x-ray crystal structures of the strained boracyclotrisiloxane (PhBO)(Ph2SiO)2 and the boracyclotetra siloxane (PhBO)(Ph2SiO)3. Inorg. Chem. 1992, 31 (14), 3034–3043. [28]. Cruz-Huerta, J.; Campillo-Alvarado, G.; Höpfl, H.; Rodríguez-Cuamatzi, P.; Reyes-Márquez, V.; Guerrero-Álvarez, J.; Salazar-Mendoza, D.; Farfán-García, N. Self-Assembly of Triphenylboroxine and the Phenylboronic Ester of Pentaerythritol with Piperazine, trans-1,4- Diaminocyclohexane, and 4-Aminopyridine. Eur J. Inorg Chem 2015, 2016 (3), 355–365. [29]. Foucher, D. A.; Lough, A. J.; Manners, I. Synthesis, properties, and the ring-ring transformation reactions of cyclic siloxanes incorporating skeletal boron atoms: x-ray crystal structures of the strained boracyclotrisiloxane (PhBO)(Ph2SiO)2 and the boracyclotetra siloxane (PhBO)(Ph2SiO)3. Inorg. Chem. 1992, 31 (14), 3034–3043. [30]. Sergeant Bull, O.; Monsuru Adewale, S.; Okpa, E. Production of Biodiesel from Waste Cooking Oil using A Zinc-Based Metal-Organic Framework (Zn-MOF) As Catalyst. SSRG International Journal of Applied Chemistry, SSRG-IJAC 2024, 11 (1), 1–6. [31]. Bull, O. S.; George, D. M. C. Assessment of Fuel Properties of Biodiesel Obtained From African Pear (Dacryodeseludis) Seeds Oil. Int. J. Adv. Res. Sci. Eng. Technol. 2015, 2 (10), 894–898. Copyright © 2025 by Authors. This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at https://www.eurjchem.com/index.php/eurjchem/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution, or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (https://www.eurjchem.com/index.php/eurjchem/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). https://www.eurjchem.com/index.php/eurjchem/terms http://creativecommons.org/licenses/by-nc/4.0 https://www.eurjchem.com/index.php/eurjchem/terms 1. Introduction 2. Experimental 2.1. Chemicals and reagents 2.2. Instrumentation 2.3. Synthesis 2.3.1. Synthesis of compound 3 (Ph6B2Si2O4) 2.3.2. Synthesis of compound 4 [Ph8B4Si2O6] L 2.3.3. Synthesis of compound 5 [4(C12H12O2Si) 3(C10H8N4)] 3. Results and discussion 3.1. Compound 4 [Ph8B4Si2O6] L 3.2. Compound 5 [4(C12H12O2Si) 3(C10H8N4)] 4. Conclusions Acknowledgements Supporting information Disclosure statement CRediT authorship contribution statement ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField18: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: PrintField28: