Synthesis, crystal structure, and Hirshfeld surface analysis of a cubane-type tetranuclear polyoxotitanate cluster


European Journal of Chemistry 16 (2) (2025) 146-153 

 

European Journal of Chemistry 
ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2025 The Authors – Atlanta Publishing House LLC – Printed in the USA.  

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https://dx.doi.org/10.5155/eurjchem.16.2.146-153.2646 

 
 

 

 

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Synthesis, crystal structure, and Hirshfeld surface analysis of  
a cubane-type tetranuclear polyoxotitanate cluster 
 
Jayanta Kumar Nath  
 

Department of Chemistry, Sreenivas Basudev Deorah College, Ulubari, Guwahati, Assam-781007, India 
 
* Corresponding author at: Department of Chemistry, Sreenivas Basudev Deorah College, Ulubari, Guwahati, Assam-781007, India.  
e-mail: jay123.nath@gmail.com (J.K. Nath). 

 
 

  

   

   

 
 10.5155/eurjchem.16.2.146-153.2646 

 
Received: 16 January 2025 
Received in revised form: 6 March 2025 
Accepted: 20 April 2025 
Published online: 30 June 2025 
Printed: 30 June 2025 

 
A cubane-type tetranuclear polyoxotitanate cluster derived from 8-(isopropoxycarbonyl)-
1-naphthoic acid is reported which is synthesized under reflux conditions in isopropanol 
(HOiPr). The ligand 8-(isopropoxycarbonyl)-1-naphthoic acid (INA) was generated in situ 
from 1,8-naphthalic anhydride and isopropyl alcohol in the reaction mixture where one of 
the carboxylate groups of 1,8-naphthalene dicarboxylic acid (generated from the ring 
opening reaction of 1,8-naphthalic anhydride) forms isopropyl ester by reacting with 
solvent isopropoxide. The solid-state structural elucidation of the cluster is achieved 
through the single crystal X-ray diffraction method, providing detailed insights into their 
molecular arrangements. Crystal data for C72H80O24Ti4: Triclinic, space group P-1 (no. 2), a = 
19.086(3) Å, b = 20.341(4) Å, c = 21.538(4) Å, α = 88.895(4)°, β = 72.158(4)°, γ = 89.049(4)°, 
V = 7958(3) Å3, Z = 4, T = 293(2) K, μ(MoKα) = 0.457 mm-1, Dcalc = 1.269 g/cm3, 64356 
reflections measured (4.42° ≤ 2Θ ≤ 54.94°), 34455 unique (Rint = 0.0458, Rsigma = 0.0752) 
which were used in all calculations. The final R1 was 0.0603 (>2sigma(I)) and wR2 was 
0.1558 (all data). In the crystal lattice, the asymmetric unit of the cluster contains two 
molecules. Various types of supramolecular interactions such as C-H···O, C-H···π, π···π and 
unusual O···O interactions are observed in the X-ray structures. All these interactions guide 
the formation of 3D supramolecular architecture in the solid state of the compound. In 
addition to these, 2D fingerprint (2D-FP) and Hirshfeld surface analysis (HSA) computations 
were used to prove and quantify various supramolecular interactions within the crystal 
lattice. 

 
Cubane 
Carboxylic acids 
Naphthalic anhydride 
Polyoxotitanate cluster 
Hirshfeld surface analysis 
Supramolecular chemistry 

Cite this: Eur. J. Chem. 2025, 16(2), 146-153 Journal website: www.eurjchem.com 

 
1. Introduction 
 

Titanium oxo clusters are intriguing molecules that often 
display properties comparable to those of bulk or nano-TiO2 
materials [1,2]. Titanium oxo clusters can be used in bulk 
materials, as catalytic sites, and in dye-sensitized materials [3-
5]. The advantage of these compounds lies in their ability to 
tailor their physicochemical, photocatalytic, and biological 
properties by modifying the core size and architecture of 
{TiaOb} and functionalizing carboxylate groups as stabilizing 
ligands [6-9], etc. Furthermore, TiO2 finds applications in 
photocatalysis, solar cells, and remediation of environmental 
pollution [10-16]. Polyoxotitanate clusters (POT) or titanium 
oxo clusters (TOCs) with well-defined structures are 
considered ideal molecular models for TiO2 materials [17,18]. 
As POTs are protected by ligands, they can provide information 
about the relationship between the structure and properties of 
TiO2 and surface structural information [9,19,20]. Furthermore, 
transition-metal-based carboxylate complexes [21-25], 
especially POT, show various supramolecular interactions and 
assemblies [26]. Naphthalene and its derivatives have been 
widely studied for their attractive photophysical properties, 
primarily because of excimer formation. The UV-visible spectra 
of 2- or 3-ring Poly Aromatic Hydrocarbons (PAHs), such as 
naphthalene, exhibit strong ultraviolet absorption from π-π* 

transitions and a distinct fine structure linked to conjugated 
aromatic bonds [27,28]. This adds additional properties to the 
cluster as a photocatalyst. Although there are several reports on 
polyoxotitanate clusters based on carboxylate ligands, POT 
formed from 1,8-naphthalene dicarboxylic acid or its 
derivatives is very rare.  

Keeping this in mind here, we report crystal structure of a 
tetranuclear cubane-type polyoxotitanate cluster of [Ti4(μ3-
O)4(μ2-INA)4(OiPr)4] {OiPr-: isopropyl alcoholate ion, INA which 
is formed by the reaction of 1,8-naphthalene dicarboxylic acid 
(formed ring opening reaction of 1,8-naphthlic anhydride) with 
solvent (Figure 1) and the core of the cluster consists of Ti4. 
 
2. Experimental 
 
2.1. Chemicals and reagents 
 

All chemicals, reagents, and solvents were purchased from 
Sigma-Aldrich or Alfa-Aesar and used as received unless 
otherwise stated. 
 
2.2. Synthesis of the Ti-cluster 
 

The cluster was synthesized using a solvothermal method 
in which titanium isopropoxide (1 mmol, 0.298 mL) was added  

ABSTRACT RESEARCH ARTICLE 

KEYWORDS 

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Jayanta Kumar Nath / European Journal of Chemistry 16 (2) (2025) 146-153 147 
 

 
2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.146-153.2646 

 
Table 1. Crystallographic parameters of the cluster. 
Compound Ti4-cluster 
Empirical formula C72H80O24Ti4 
CCDC deposition number 2405481 
formula weight 1610.85 
Temperature/K  293(2)  
crystal system Triclinic 
space group P-1 
a/Å  19.086(3)  
b/Å  20.341(4)  
c/Å  21.538(4)  
α/°  88.895(4)  
β/°  72.158(4)  
γ/°  89.049(4)  
V/Å3 7958(3) 
Z 4 
Density (g cm-3) 1.269 
μ/mm-1  0.457  
F(000)  3168.0  
Crystal size/mm3  0.19 × 0.17 × 0.15  
Rradiation type MoKα (λ = 0.71073) 
2Θ range for data collection/°  4.42 to 54.94  
Index Ranges -24≤ h ≤ 24, -26≤ k ≤26, -27≤ l ≤ 27 
Reflections collected  64356  
Independent reflections  34455 [Rint = 0.0458, Rsigma = 0.0752]  
Data/Restraints/Parameters 34455/0/ 1833 
Goodness-of-fit on F2  1.047  
Final R indexes [I>=2σ (I)]  R1 = 0.0603, wR2 = 0.1382  
Final R indexes [all data]  R1 = 0.0922, wR2 = 0.1558  
Largest diff. peak/hole / e Å-3  0.45/-0.39  
CCDC deposition number 2405481 
 

Ti

O Ti

O

O Ti

Ti O

O O

O O

O

O

O

O

O

O

O

OO OO

+ Ti-(iospropoxide)3
2-Propanol

90 oC, 12 hr

 
 

Figure 1. Synthesis of the Ti cluster. 
 
to a solution of 1,8-naphthalic anhydride (1 mmol, 0.298 g) in 
2-propanol and the mixture was heated at 90 °C for 24 hr. After 
being cooled to room temperature, colorless prismatic type 
crystals were obtained. Yield 78%. 
 
2.3. X-ray crystallography 
 

The cluster crystal that has approximate dimensions of 0.19 
mm × 0.17 mm × 0.15 mm was sealed in a glass capillary. 
Crystallographic data and structure refinement parameters for 
the cluster at 293(2) K are given in Table 1. X-ray diffraction 
data were collected on a Rigaku Inc., 2008 Bruker SMART Apex 
II CCD diffractometer using Mo Kα (λ = 0.71073 Å) radiation and 
X-ray diffraction data for the crystal were collected using 
Bruker SMART software [29]. This software was also used for 
indexing and determination of the unit cell parameters. Cell 
structures were solved by direct method and refined using full 
matrix least squares against F2 of all data, using SHELXTL [30] 
and Olex2-1.5 [31] software. All non-H atoms were refined by 
full-matrix least squares in anisotropic symmetry, while all H 
atoms were refined in an isotropic approximation, against F2 of 
all reflections. Some hydrogen atoms attached to these atoms 
were treated as ‘riding’ in calculated positions. As the 
disordered solvent molecules could not be assigned, a Platon-
PWT 2023.1 [32] squeeze method is applied to remove the 
electron density. From the squeeze result, it is observed that a 
total of 36 electron counts was removed, which is equal to one 
and half of isopropanol molecules (24 electrons + 12 electrons 

= 36 electrons). The molecular structures were drawn at 
Mercury 4.2.0 [33], Diamond software version 3.2 [34]. The 
selected bond distances (Å) and angles (°) of the Ti-cluster are 
given in Table 2. 
 
3. Results and discussion 
 
3.1. Crystal structure 
 

The structure of the cluster has been established by single 
crystal X-ray analysis having composition [Ti4(INA)4(µ3-
O)4(OiPr)4]·1.5C3H8O and crystallized in the P-1 triclinic space 
group. The asymmetric unit of the cluster contains two 
molecules of the clusters where each cluster contains four 
Ti(IV) ions, four coordinated µ3-INA ligands, four coordinated 
isopropoxide ions with 3 bridges, four µ3-bridged oxide ions 
(Figure 2a). In addition to these, isopropanol molecules of 
crystallization are also present in its asymmetric unit. The 
coordination polyhedra around the metal center of the cluster 
are shown in Figure 2c. The {Ti4(μ3-O4)} core forms a 
tetragonally distorted cube with alternately arranged Ti and O 
atoms organized into Ti2O2 faces, linked by four carboxylate 
groups. The Ti ions form a cubane type structure with the oxide 
ions, as shown in Figure 2b. The Ti···Ti distance in the cubane-
type structure is in the range of 2.9167(8)-3.045(8) Å. Each Ti4+ 
ion in the cluster is in a {TiO6} environment and adopted a 
distorted octahedra coordination geometry around the metal 
center.  



148 Jayanta Kumar Nath / European Journal of Chemistry 16 (2) (2025) 146-153 
 

 
2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.146-153.2646 

 
Table 2. Selected bond distances (Å) and angles (°) of the Ti-cluster. 
M-L dM-L(Å) ∠L-M-L Angle (°) ∠L-M-L Angle (°) ∠L-M-L Angle (°) 
Ti1-O24 3.045(8) O24-Ti1-O26 63.2(3) O30-Ti4-O19 162.75(8) O14-Ti7-O2 91.55(8) 
TI1-O26 2.0576(7) O24-Ti1-O32 82.42(8) O30-Ti4-O21 88.27(7) O14-Ti7-O5 161.50(8) 
Ti1-O29 1.8958(18) O26-Ti1-O32 110.9(2) O30-Ti4-O31 81.67(7) O14-Ti7-O12 81.36(7) 
Ti1-O31 1.9509(18) O29-Ti1-O24 90.69(8) O31-Ti4-O21 82.95(7) O14-Ti7-O13 80.08(8) 
Ti1-O32 2.1082(18) O29-Ti1-O26 161.71(8) O32-Ti4-O19 90.34(8) O18-Ti7-O2 98.47(10) 
Ti1-O48 1.745(2) O29-Ti1-O31 80.44(7) O32-Ti4-O21 163.33(8) O18-Ti7-O5 92.76(9) 
Ti2-O22 2.0408(19) O29-Ti1-O32 81.70(7) O32-Ti4-O30 81.34(8) O18-Ti7-O12 174.72(9) 
Ti2-O23 2.0313(19) O31-Ti1-O24 161.89(8) O32-Ti4-O31 82.66(7) O18-Ti7-O13 99.09(9) 
Ti2-O29 2.1079(17) O31-Ti1-O26 87.29(8) O46-Ti4-O19 94.43(9) O18-Ti7-O14 103.83(9) 
Ti2-O30 1.9224(17) O31-Ti1-O32 80.70(7) O46-Ti4-O21 90.43(9) O3-Ti8-O6 96.41(8) 
Ti2-O32 1.9457(19) O48-Ti1-O24 133.3(3) O46-Ti4-O30 102.26(9) O3-Ti8-O14 81.66(7) 
Ti2-O39 1.7510(19) O48-Ti1-O26 91.88(9) O46-Ti4-O31 172.23(8) O6-Ti8-O14 82.55(8) 
Ti3-O20 2.0774(19) O48-Ti1-O29 104.03(9) O46-Ti4-O32 104.46(9) O11-Ti8-O3 90.61(8) 
Ti3-O25 2.0556(19) O48-Ti1-O31 103.15(9) O8-Ti5-O7 96.41(8) O11-Ti8-O6 162.17(8) 
Ti3-O29 1.9239(18) O48-Ti1-O32 173.48(9) O8-Ti5-O11 82.20(8) O11-Ti8-O12 81.12(8) 
Ti3-O30 2.0838(17) O22-Ti2-O29 82.08(7) O11-Ti5-O7 162.70(8) O11-Ti8-O14 82.28(7) 
Ti3-O31 1.9111(18) O23-Ti2-O22 94.89(8) O13-Ti5-O8 91.24(8) O12-Ti8-O3 162.51(8) 
Ti3-O47 1.7622(19) O23-Ti2-O29 82.34(7) O13-Ti5-O11 82.66(7) O12-Ti8-O6 87.53(8) 
Ti4-O19 2.057(2) O30-Ti2-O22 161.04(8) O13-Ti5-O14 80.85(8) O12-Ti8-O14 81.97(7) 
Ti4-O21 2.0903(18) O30-Ti2-O23 91.47(8) O14-Ti5-O7 87.44(8) O16-Ti8-O3 94.40(8) 
Ti4-O30 1.9261(18) O30-Ti2-O29 81.09(7) O14-Ti5-O8 162.59(8) O16-Ti8-O6 89.02(9) 
Ti4-O31 2.0818(18) O30-Ti2-O32 80.18(7) O14-Ti5-O11 81.43(7) O16-Ti8-O11 106.82(9) 
Ti4-O32 1.8963(18) O32-Ti2-O22 88.51(8) O17-Ti5-O7 89.25(8) O16-Ti8-O12 102.72(8) 
Ti4-O46 1.7656(19) O32-Ti2-O23 161.95(8) O17-Ti5-O8 95.75(9) O16-Ti8-O14 170.21(9) 
Ti5-O7 2.0960(19) O32-Ti2-O29 80.57(7) O17-Ti5-O11 171.74(8)   
Ti5-O8 2.054(2) O39-Ti2-O22 92.55(9) O17-Ti5-O13 105.43(9)   
Ti5-O11 2.0848(17) O39-Ti2-O23 95.19(9) O17-Ti5-O14 101.29(9)   
Ti5-O13 1.8929(18) O39-Ti2-O29 173.85(8) O1-Ti6-O13 81.91(8)   
Ti5-O14 1.9380(19) O39-Ti2-O30 104.66(9) O4-Ti6-O1 96.36(9)   
Ti5-O17 1.7679(19) O39-Ti2-O32 102.38(9) O4-Ti6-O13 82.15(8)   
Ti6-O1 2.551(7) O20-Ti3-O30 83.76(7) O11-Ti6-O1 88.18(8)   
Ti6-O4 2.024(2) O25-Ti3-O20 99.17(8) O11-Ti6-O4 161.39(8)   
Ti6-O11 1.9558(18) O25-Ti3-O30 81.95(7) O11-Ti6-O13 80.64(7)   
Ti6-O12 1.9042(19) O29-Ti3-O20 86.58(8) O12-Ti6-O1 161.47(8)   
Ti6-O13 2.1063(18) O29-Ti3-O25 161.94(8) O12-Ti6-O4 90.30(9)   
Ti6-O15 1.7564(19) O29-Ti3-O30 81.68(7) O12-Ti6-O13 81.91(8)   
Ti7-O2 2.024(2) O31-Ti3-O20 162.11(8) O15-Ti6-O1 92.30(9)   
Ti7-O5 2.065(2) O31-Ti3-O25 89.46(8) O15-Ti6-O4 98.40(9)   
Ti7-O12 2.1150(18) O31-Ti3-O29 80.75(7) O15-Ti6-O11 99.44(8)   
Ti7-O13 1.9465(19) O31-Ti3-O30 81.97(7) O15-Ti6-O12 103.83(9)   
Ti7-O14 1.9152(18) O47-Ti3-O20 89.97(9) O15-Ti6-O13 174.21(9)   
Ti7-O18 1.757(2) O47-Ti3-O25 94.08(9) O2-Ti7-O5 94.09(9)   
Ti8-O3 2.0503(19) O47-Ti3-O29 103.08(9) O2-Ti7-O12 82.20(8)   
Ti8-O6 2.062(2) O47-Ti3-O30 171.92(9) O5-Ti7-O12 81.97(8)   
Ti8-O11 1.9042(19) O47-Ti3-O31 105.11(9) O13-Ti7-O2 161.92(8)   
Ti8-O12 1.9252(18) O19-Ti4-O21 96.04(8) O13-Ti7-O5 89.37(9)   
Ti8-O14 2.0828(18) O19-Ti4-O31 82.29(7) O13-Ti7-O12 80.72(7)   
 
Table 3. Some of the hydrogen bond parameters such as C-H···O, and C-H⋅⋅⋅π, π···π contacts for the cluster. 
Donor-H···Acceptor D···A (Å) D-H···A (Å) Angle A···H···A (°) 
C104-H10A···O41 2.53  3.055(5)  115 
C104-H10C···O29  2.39  3.312(4) 160 
C111-H11A···O36  2.46  3.038(6)  118 
C117-H11S···O10  2.48  3.035(5) 117 
C121-H12C···O34  2.58  3.103(7)  114 
C133-H13I···O45  2.48 3.045(8)  117 
C139-H13P···O42  2.42 2.992(8)  118 
C146-H14R···O38  2.53 3.035(8)  113 
C19-H19···O45  2.38 3.045(8)  164 
C28-H28···O2  2.43 2.756(5)  101 
C28-H28···O42  2.32 3.148(6) 148 
C30-H30···O8 2.47 2.789(5)  100 
C30-H30···O10  2.35 3.257(5) 164 
C36-H36···O4  2.47 2.787(4)  100 
C36-H36···O38  2.28 3.140(6) 155 
C54-H54···O25  2.43 2.757(4) 101 
C54-H54···O36  2.33 3.241(4) 167 
C59-H59···O23  2.42 2.749(4) 100 
C59-H59···O41 2.57 3.312(5) 137 
C73-H73···O19 2.43  2.759(4)  100 
C73-H73···O34  2.28 3.176(5) 161 
C77-H77···O28  2.46 2.823(5)  100 
C86-H86···O24  2.46 2.775(4) 100 
C86-H86···O28  2.31 3.184(5) 156 
C88-H88···O9 2.49 3.407(5) 167 
C94-H94···O41  2.46 2.788(5)  100 
C12- H12···O36 2.67 3.501(4) 148.71 
C123-H12I···O15 2.69 3.650 (5) 174.11 
C64-H64···O10 2.66 3.373(5) 133.50 
 



Jayanta Kumar Nath / European Journal of Chemistry 16 (2) (2025) 146-153 149 
 

 
2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.146-153.2646 

Table 3. (Continued). 
C-H···Cg  C···Cg (Å) 
C137-H13E···Cg 3.766 
C111-H11B···Cg 3.797 
C89-H89··· Cg 3.924 
Cg···Cg 3.587 
Cg = Center of gravity of the ring. 
 

 
(a) 

 
(b) 

 

 
(c) 

 
Figure 2. (a) Ellipsoid view (40% thermal ellipsoid) of the cluster, (b) Different coordination environment around Ti center, (c) Coordination polyhedra around 
Ti. 

 
The octahedral geometry is satisfied by two O atoms from 

two carboxylate groups of two different ligands and three O 
atoms from three oxide ligands, as shown in Figure 2b. Each 
carboxylate group of the ligand acts as a bridging ligand 
between two Ti4+ ions in which Ti binds with O with unequal 
bond length ranging from 2.024-2.090 Å. Polyhedral structure 
of the cluster around the Ti center has been shown in the Figure 
4a. These bonds are little shorter than some reported transition 
metal-carboxylate bond [21]. The core structure is a distorted 
cubane-type structure which is reflected from the unequal Ti-
oxo bond length ranging from dTi-O = 1.896-2.108 Å and from the 
Ti-O-Ti bond angle ∠Ti-O-Ti which vary from 97.3 to 98.9° 
whereas ∠O-Ti-O bond angles vary from 80.70° to 82.67°. The 
Ti-Ti distances corresponding to the diagonal of rectangular 
Ti2O2 faces are close to 2.917 Å, while Ti−Ti distances between 
atoms belonging to different faces are close to 3.045 Å. The four 
terminal Ti-O bond lengths of coordinated isopropoxide ions 
are different and shortest which vary from 1.745 Å to 1.766 Å 
in one unit, whereas in the other unit this distance varies from 
1.756 to 1.775 Å. The detailed metal ligand bond parameters 
are shown in Table 2. These parameters are comparable to the 

reported Ti clusters [35]. There are several supramolecular 
(intermolecular) interactions that exist in the solid-state 
structure of the cluster, such as C-H···O and C-H···π (both 
aromatic and aliphatic C-H) interactions. The weak donor-
acceptor distance of these C-H···O hydrogen bonds are C64-
H64···O10 (dC64-O10 = 3.373 (5) Å), C12-H12···O36 bond (dC12-O36 
= 3.501(4) Å), C123-H12I···O15 (dC123-O15 = 3.650 (5) Å) and 
C88-H88···O9 (dC88-O9 = 3.407(5) Å) (Figure 3a,b). The bond 
angle of these hydrogen bonds are <C12-H12-O36 = 148.71°, 
<C123-H12I-O15 = 174.11°, C64-H64···O10 = 133.50° and 
<C88-H88-O9 = 167°. The H bonding table is shown in Table 3. 

An unusual intramolecular O···O interaction is observed 
with distance ranging from 2.831 to 2.911 Å in one unit and this 
distance in the other unit vary from 2.898 to 3.019 Å. In addition 
to these H bonds, the crystal structure is further stabilized by C-
H···π with dC···Cg (Cg means center of gravity of the ring) ranging 
from 3.766 to 4.221 Å and π···π interaction with dCg···Cg distance 
of 3.857 Å which has been shown in Figure 4b. All these 
interactions lead to the formation of a 3D supramolecular 
structure in the solid state (Figure 3c), and the 3D architecture 
space fill model is also shown in Figure 3d. 



150 Jayanta Kumar Nath / European Journal of Chemistry 16 (2) (2025) 146-153 
 

 
2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.146-153.2646 

  

 
(a) 

 

 
(b) 

 

 
(c) 

 
(d) 

 
Figure 3. (a) Aliphatic C-H···π, C-H···O and O···O interactions, (b) Aromatic C-H···O, C-H···π interactions, (c) 3D supramolecular structure, and (d) packing diagram 
(space fill model). 
 

(a) 
 

(b) 
 

Figure 4. (a) Polyhedral structure of the cluster around the Ti center and (b) π···π interaction in the cluster. 
 

3.2. Hirshfeld surface and 2-dimensional fingerprint plot 
analysis 
 

Hirshfeld surface analysis was performed and associated 
two-dimensional fingerprint plots were generated using 
CrystalExplorer 21 [36], with a standard resolution of the three-
dimensional dnorm surfaces plotted over a fixed color scale of -
0.1614 to 6.8691 a.u. Figure 5 highlights various contacts on the 
molecular Hirshfeld surface, mapped using standard indices 
such as dnorm, de, shape index, curvedness, and fragment patches. 

The different colors of the Hirshfeld surface mapped over dnorm 
relate to different distances. A red surface indicates distances 
shorter than the sum of van der Waals radii (close and strong 
intermolecular interactions such as C-H···O), a white surface 
indicates distances near the sum of van der Waals radii (it 
represents neutral areas where weak van der Waals 
interactions), and a blue surface indicates distances longer than 
the sum of van der Waals radii (it corresponds to areas of 
positive electrostatic potential, meaning they are electron 
deficient).  



Jayanta Kumar Nath / European Journal of Chemistry 16 (2) (2025) 146-153 151 
 

 
2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.146-153.2646 

 

   
dnorm de di 

   
Fragment patch Shape index Curveness 

 
Figure 5. Three-dimensional Hirshfeld surfaces mapped with dnorm, de, shape-index surfaces showing π⋯π interactions, with red and blue triangles within a black 
ellipse indicating bumps and hollow regions, respectively, evidencing the π⋯π stacking area on the Hirshfeld surfaces, curvedness with flat areas emphasizing 
the ring contributions in π-stacking interactions and fragment patches showing different colors of fragment patches represent molecular interactions across the 
molecular region of the compounds of Ti-cluster. 
 

   
 

   
 
Figure 6. The full 2D-FP for the Ti cluster showing all interactions and delineated into H⋯H, C···H/H···C, O···H/H···O, Ti···O/O···Ti and C···C, interactions. The di 
and de values are the closest internal and external distances (in Å) from given points on the HS contacts. 

 
Certain areas on the dnorm surfaces represent H···H close 

contacts and non-classical hydrogen bond interactions. The 
surface of the shape index surface shows complementary 
triangular pairs upon 180° rotation, a key feature of π···π 
stacking essential for the molecular stability and self-assembly 
of aromatic compounds [37,38]. The red and blue triangles 
within a black ellipse indicate bumps and hollow regions, 
respectively, evidencing the π⋯π stacking area on the Hirshfeld 

surfaces. Curvedness surfaces of the cluster further confirm 
π···π interactions, with flat areas indicating a close proximity of 
the aromatic ring. These interactions significantly impact 
molecular conformation and reactivity. Different colors of 
fragment patches represent molecular interactions across the 
molecular region. The volume within the Hirshfeld surface is 
computed to be 3438.74 Å3, with an area of 1677.09 Å2.  



152 Jayanta Kumar Nath / European Journal of Chemistry 16 (2) (2025) 146-153 
 

 
2025 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.16.2.146-153.2646 

This analysis provides more information about the 
intermolecular interactions within the crystal lattice of the 
cluster. The main objective of this study was to quantitatively 
analyze the various intermolecular interactions, shedding light 
on the subtle contacts that intricately shape the molecule. 
Notably, the light red spots on the HS predominantly 
correspond to significant types of intermolecular interactions: 
C-H···O, C-H···π and π···π.  

Directional dihydrogen intramolecular interactions, such as 
C-H⋯H-C, have been observed in the crystal structure, as 
illustrated in Figure 5. These interactions were theoretically 
reported by Almeida et al. [39], demonstrating that dihydrogen 
contacts are sufficiently strong and directional to stabilize 
molecular arrangements in crystals [40]. Additionally, 
theoretical studies have explored the behavior of dihydrogen 
contacts in greater detail [41,42]. All these interactions 
contribute to the stability of a compound in the solid state [43]. 
In our cluster, the H⋯H interaction is found to be the most 
prominent interaction, which contributes 83.3% of the overall 
interaction strength. These provide stability to the overall 
crystal packing which is due to a large number of the short 
interatomic H⋯H contacts that are located in the middle region 
of the fingerprint plot reflected in the plot [44,45]. This 
indicates that weak van der Waals forces significantly 
contribute to the compound's cohesive nature. [46] 

The other contributions such as C···H/H···C, O···H/H···O, 
O···O and C···C contacts are 9.6, 4.5, 0.7 and 0.4%, respectively 
(Figure 6). An unusual Ti···O/O···Ti interaction is observed 
which contributes 1.5% to the overall crystal packing [47]. The 
C···C interaction signifies the π···π stacking interaction in the 
solid-state structure. and this interaction is essential for the 
molecular stability and self-assembly of aromatic compounds 
[48-51]. 
 
4. Conclusions 
 

In conclusion, a tetranuclear polyoxotitanate cluster 
exhibiting a cubane-type structure based on a naphthalene 
carboxylate mono ester-based ligand was successfully 
synthesized and subsequently characterized with SCXRD. The 
solid-state X-ray crystal structure of the cluster forms 3D 
supramolecular structures, driven by noncovalent interactions 
like C–H···O, C–H···π, and π···π interactions. The primary 
contributor to the solid-state structures was identified through 
the 2D fingerprint plot in Hirshfeld surface analysis. Among all 
interactions, dihydrogen interactions contribute the most, 
playing a crucial role in stabilizing the overall packing of the 
solid-state structure. Because of the presence of naphthalene 
rings in the cluster, this material could provide an arena for 
researchers to delve into a novel direction in the advancement 
of the photocatalyst molecule and provides insights into 
structural diversity and supramolecular phenomena. 
 
Acknowledgements 
 
The author thanks ANRF (SERB-TARE) for research grant with file no. 
TAR/2023/000221. The author acknowledges Sreenivas Basudev Deorah 
College for laboratory facility and the Indian Institute of Technology 
Guwahati for single crystal X-ray Diffraction facility. 
 
Supporting information  
 
CCDC-2405481 contains 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. 
 
ORCID  and Email  
 
Jayanta Kumar Nath 

 jay123.nath@gmail.com   

 https://orcid.org/0000-0002-0477-5861  
 
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	1. Introduction
	2. Experimental
	2.1. Chemicals and reagents
	2.2. Synthesis of the Ti-cluster
	2.3. X-ray crystallography

	3. Results and discussion
	3.1. Crystal structure
	3.2. Hirshfeld surface and 2-dimensional fingerprint plot analysis

	4. Conclusions
	Acknowledgements
	Supporting information
	Disclosure statement
	ORCID  and Email
	References

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