Basic Building Units Research Articles

K4Cd3Ge4O13: A Congruent-Melting Germanate Nonlinear Optical Crystal with a Moderate Second-Harmonic Generation Intensity and Broad Transparent Window.

Mid-infrared (IR) nonlinear optical (NLO) materials have generated extensive research interest because of their crucial role in laser technology applications. Here, we report the synthesis of a novel cadmium germanate NLO crystal, K4Cd3Ge4O13, using spontaneous crystallization. K4Cd3Ge4O13 demonstrates a distinct three-dimensional structural framework characterized by twisted [Ge4O13] and [Cd3O10] clusters, composed of [GeO4], [CdO4], [CdO5], and [CdO6] basic building units, respectively, which represents an unprecedented structural feature. The title compound undergoes a desirable congruent melting behavior at about 727 °C. Notably, K4Cd3Ge4O13 demonstrates a short UV cutoff edge at 261 nm, coupled with a wide energy gap of 4.4 eV, and maintains an extended IR transparency window at around 6.0 μm. More importantly, it demonstrates a strong second-harmonic generation activity comparable to that of KH2PO4 (KDP) at 1064 nm. Theoretical analyses further elucidate that the remarkable optical performances of K4Cd3Ge4O13 are predominantly attributed to the cooperative effects of Ge-O and Cd-O bond-based motifs. These desired characteristics underscore the potential of K4Cd3Ge4O13 as a good candidate material for mid-IR NLO applications.

Temperature-dependent diffraction studies on the stannides Sr3Rh4Sn4, Sr3Ir4Sn4 and Sr2.43Eu0.57Ir4Sn4

Abstract The stannides Sr3Rh4Sn4 and Sr2.43Eu0.57Ir4Sn4 (Na3Pt4Ge4-type, space group I 4 ‾ $\overline{4}$ 3m) were synthesized by induction-melting of the elements in sealed tantalum tubes followed by an annealing sequence to increase the crystallinity. Their polycrystalline samples were characterized by powder X-ray diffraction and the structures were refined from single crystal X-ray diffractometer data. The basic building units are [Rh4Sn4] respectively [Ir4Sn4] stellae quadrangulae which condense to rigid three-dimensional networks. A striking crystal chemical feature of the Na3Pt4Ge4-type phases are pronounced anisotropic displacements of the divalent cations. Additional structure refinements of Sr3Rh4Sn4 and Sr2.43Eu0.57Ir4Sn4 and the previously reported stannide Sr3Ir4Sn4 at 90 K reveal less anisotropic behavior in going to lower temperatures.

CdInO(BO3): An oxyborate birefringent material explored from d10 metal compounds

Birefringent crystals are particularly important in optical communication and laser industries. Herein, we report the synthesis, structures, optical properties, and theoretical analyses of an oxyborate birefringence material CdInO(BO3). It has an interesting sandwich-like basic building unit (BBU) constructed by [CdO4]6− chains and [InO4]5− chains. CdInO(BO3) possesses an experimental band gap of 3.65 eV and an ultraviolet (UV) cut-off edge about 295 nm. Moreover, it exhibits a large birefringence (0.136@1064 nm), which mainly originates from the parallel arrangement of the isolated [BO3] groups. This discovery indicates that CdInO(BO3) can be a promising birefringent material.

Cs3In(In4Se7)(P2Se6): A Multi-Chromophore Chalcogenide with Excellent Nonlinear Optical Property Designed by Group Grafting.

Non-centrosymmetric (NCS) and polar materials capable of exhibiting many important functional properties are indispensable for electro-optical technologies, yet their rational structural design remains a significant challenge. Here, we report a "group grafting" strategy for designing the first multi-chromophore selenophosphate, Cs3In(In4Se7)(P2Se6), that crystallizes in a NCS and polar space group of Cm. The structure features a unique basic building unit (BBU) [In(In4Se10)(P2Se6)], formed through "grafting [In4Se10] supertetrahedra on the root of [In(P2Se6)2] groups". Theoretical calculations confirm that this [In(In4Se10)(P2Se6)] BBU can achieve a "1+1>2" combination of properties from two chromophores, [In4Se10] supertetrahedron and ethane-like [P2Se6] dimer. That makes Cs3In(In4Se7)(P2Se6) exhibit excellent linear and nonlinear optical (NLO) properties, including a strong second harmonic generation (SHG) response (~6×AgGaS2), a large band gap (2.45 eV), broad infrared (IR) transmission (up to 19.5 μm), a significant birefringence (0.26 @1064 nm) as well as the congruently-melting property at ~700 °C. Therefore, Cs3In(In4Se7)(P2Se6) will be a promising NLO crystal, especially in the IR region, and this research also demonstrates that "group grafting" will be an effective strategy for constructing novel polar BBUs with multi-chromophore to design NCS structures and high-performance IR NLO materials.

Cs3In(In4Se7)(P2Se6): A Multi‐Chromophore Chalcogenide with Excellent Nonlinear Optical Property Designed by Group Grafting

AbstractNon‐centrosymmetric (NCS) and polar materials capable of exhibiting many important functional properties are indispensable for electro‐optical technologies, yet their rational structural design remains a significant challenge. Here, we report a “group grafting” strategy for designing the first multi‐chromophore selenophosphate, Cs3In(In4Se7)(P2Se6), that crystallizes in a NCS and polar space group of Cm. The structure features a unique basic building unit (BBU) [In(In4Se10)(P2Se6)], formed through “grafting [In4Se10] supertetrahedra on the root of [In(P2Se6)2] groups”. Theoretical calculations confirm that this [In(In4Se10)(P2Se6)] BBU can achieve a “1+1>2” combination of properties from two chromophores, [In4Se10] supertetrahedron and ethane‐like [P2Se6] dimer. That makes Cs3In(In4Se7)(P2Se6) exhibit excellent linear and nonlinear optical (NLO) properties, including a strong second harmonic generation (SHG) response (~6×AgGaS2), a large band gap (2.45 eV), broad infrared (IR) transmission (up to 19.5 μm), a significant birefringence (0.26 @1064 nm) as well as the congruently‐melting property at ~700 °C. Therefore, Cs3In(In4Se7)(P2Se6) will be a promising NLO crystal, especially in the IR region, and this research also demonstrates that “group grafting” will be an effective strategy for constructing novel polar BBUs with multi‐chromophore to design NCS structures and high‐performance IR NLO materials.

Efficient Room Temperature Ethanol Vapor Sensing by Unique Fractal Features of Tin Oxide

Fractals are complex structures that repeat themselves at several scales. Nature exhibits these in many forms like snowflakes, mountains, coastlines, the human brain/lungs/ nervous system, and many more. It appears that these are nature’s organic way of growth. Thus, there is an underlying science that works to grow or create these self-similar patterns. In this work, tin oxide-based fractals have been grown under laboratory conditions and applied to a gas-sensing field. The facile growth methodology successfully grows fractals on a large scale. The tin oxide fractals have unique basic building units that connect and grow in different directions. These tin oxide fractals have successfully sensed ethanol vapors in the range of 20 ppm to 100 ppm. The best sensing response has also detected ethanol vapors as low as 10 ppm at room temperature with response and recovery times of 18 ± 3 s and 22 ± 5 s, respectively. The best sensing response recorded for such sensors was under 12 s. The characteristic fractal growth is attributed as the defining factor that enhances ethanol sensing at room temperature.

LiASi2O5 (A = K, Rb): Effects of cations on crystal structure and optical properties

Tetrahedral basic building units are important for the design of new nonlinear optical materials. In this paper, two alkali metal silicates have been reported to have differentiated symmetry and optical properties. LiKSi2O5 crystallizes in the monoclinic system of P21 with the ultraviolet cutoff of 255 nm; LiRbSi2O5 crystallizes in the orthorhombic system of Pca21 with the ultraviolet cutoff of 240 nm. The calculation results show that the second harmonic generation coefficients and the wavelengths of phase matching for LiKSi2O5 are d16 = 0.30 pm/V and 585 nm, while that for LiRbSi2O5 are d24 = 0.38 pm/V and 446 nm, respectively. Hence, the different radii of cations lead to different coordination environments, which will affect the connection styles further influences the symmetries and optical properties of the compounds. It is confirmed that simple ion substitution can change the optical properties, which provides a feasible way for the modulation of nonlinear optical property.

Bioinspired Amino Acid Based Materials in Bionanotechnology: From Minimalistic Building Blocks and Assembly Mechanism to Applications.

Inspired by natural hierarchical self-assembly of proteins and peptides, amino acids, as the basic building units, have been shown to self-assemble to form highly ordered structures through supramolecular interactions. The fabrication of functional biomaterials comprised of extremely simple biomolecules has gained increasing interest due to the advantages of biocompatibility, easy functionalization, and structural modularity. In particular, amino acid based assemblies have shown attractive physical characteristics for various bionanotechnology applications. Herein, we propose a review paper to summarize the design strategies as well as research advances of amino acid based supramolecular assemblies as smart functional materials. We first briefly introduce bioinspired reductionist design strategies and assembly mechanism for amino acid based molecular assembly materials through noncovalent interactions in condensed states, including self-assembly, metal ion mediated coordination assembly, and coassembly. In the following part, we provide an overview of the properties and functions of amino acid based materials toward applications in nanotechnology and biomedicine. Finally, we give an overview of the remaining challenges and future perspectives on the fabrication of amino acid based supramolecular biomaterials with desired properties. We believe that this review will promote the prosperous development of innovative bioinspired functional materials formed by minimalistic building blocks.

Dynamic context modeling based lightweight high-resolution network for dense prediction

Recent research shows that high-resolution networks can provide representative multi-scale features for vision tasks. However, high-resolution-based architectures are weak in capturing spatial long-range information, and they are computationally expensive. To alleviate these problems and encourage the engineering applications of dense prediction, based on vanilla high-resolution network, this paper presents a novel efficient architecture for dense prediction, namely Dynamic context modeling based lightweight High-Resolution Network (Dynamic-HRNet). In particular, the network consists of two key components: (i) dynamic split convolution, a more efficient and flexible convolution compared to the standard convolution, which could be conveniently embedded into other networks, and (ii) adaptive context modeling, which adaptively captures local and global contextual information to enrich the representation in parallel. Using the above two components, two lightweight blocks are designed that serve as the basic building units of Dynamic-HRNet, termed dynamic multi-scale context block and dynamic global context block, respectively. Extensive experiments demonstrate that the proposed Dynamic-HRNet, as a backbone, achieves significant superiority in popular benchmarks for human pose estimation (70.6% AP on COCO dataset and 87.6% PCKh on MPII dataset) and semantic segmentation (75.3% MIoU on Cityscapes dataset). Considering both efficiency and accuracy, it outperforms the most advanced lightweight architectures.

Targeting Oxide Concentration in Tantalum Oxide-Fluoride Anions

The design of both molecular and non-molecular solid materials with specific properties fundamentally relies on the controlled synthesis of crystals with desired functional groups, bonding motifs, polarity, chirality, and more. To this end, fluoride and oxide-fluoride anions have been utilized as basic building units (BBUs) in the synthesis of noncentrosymmetric racemic materials for their ability to create polar axes that facilitate the breaking of an inversion center as demonstrated in a series of compounds with [MF6]2- anions (M = Ti, Zr, Hf). Targeting an analog with a [TaOF5]2- anion, the phase space of (CuO, Ta2O5)/bpy/HF(aq)/H2O (bpy = 2,2′-bipyridine) was investigated and three new compounds with Cu-bpy cations and Ta-fluoride or Ta-oxyfluoride anions were synthesized: [Cu(bpy)2][TaF6], [Cu(bpy)2][Ta2OF10], and [Cu(bpy)F(H2O)2]2[TaF7]∙H2O with the anions [TaF6]-, [Ta2OF10]2-, and [TaF7]2-, respectively. The formation of these anions was found to be a product of both the concentration of hydrofluoric acid in solution and the ratio of metal-oxide starting materials to ligand. This work contributes to the understanding of mixed anion formation in the solid state.

Ba3.75MgB7O14F2.5: A Mixed Alkaline-Earth Metal Borate Fluoride with Short Ultraviolet Cutoff Edge and Large Birefringence.

Fluorine-containing borate crystal materials are particularly attractive due to their rich structural chemistry and excellent properties for optical applications. In this work, a new compound Ba3.75MgB7O14F2.5 has been synthesized through the high-temperature solution method. In the crystal structure of Ba3.75MgB7O14F2.5, the [B7O14] basic building unit and the [MgO3F3] octahedra are interconnected to create a complex three-dimensional network. The structural feature of the less commonly observed [B7O14] units is discussed, and it has been found that such units in Ba3.75MgB7O14F2.5 are most conducive to achieving large birefringence. In addition, Ba3.75MgB7O14F2.5 exhibits good thermal stability, a short ultraviolet cutoff of 203 nm, and large birefringence (0.081@546 nm), indicating its potential as a new UV birefringent crystal.

Synthesis, crystal and electronic structure of the Zintl phase Ba16Sb11. A case study uncovering greater structural complexity via monoclinic distortion of the tetragonal Ca16Sb11 structure type.

AbstractThe binary Zintl phase Ba16Sb11 has been synthesized and structurally characterized. Detailed studies via single‐crystal X‐ray diffraction methods indicate that although Ba16Sb11 appears to crystallize in the tetragonal Ca16Sb11 structure type (space group P 21m with a=13.5647(9) Å, c=12.4124(12) Å, Z=2, R1=3.14 %; wR2=4.77 %), there exists an extensive structural disorder. Some Ba16Sb11 crystals were found to be monoclinic and the structure was solved and refined in space group P21 (a=18.3929(12) Å, b=13.5233(8) Å, c=18.3978(12) Å, β=94.6600(10)°; Z=4, R1=5.84 %; wR2=9.58 %). The latter corresponds to a 2‐fold superstructure of the tetragonal one, which provides a disorder‐free structural model. In both descriptions, the disordered tetragonal and the ordered monoclinic superstructure, the basic building units that make up the structure of this Ba‐rich compound are pairs of face‐shared square antiprisms of Ba atoms, which are centered by Sb atoms. The dimerized antiprisms are linked into parallel chains via square prisms of Ba atoms, which are also centered by Sb atoms. The Zintl concept can be applied in a straightforward manner and as result, the structure of Ba32Sb22 (=2×Ba16Sb11) can be rationalized as (Ba2+)32(Sb3−)20[Sb2]4−. The partitioning of the valence electrons is done taking into an account the homoatomic Sb−Sb contacts (d=3.01 Å), which can be clearly distinguished in the lower symmetry space group. Electronic structure calculations of Ba16Sb11 are in good accordance with the Zintl rationalization and predict a semiconductor with a band gap of 0.77 eV.

Mono‐ and Bi‐Dentate Chiral Ligands Lead to Efficient Circularly Polarized Luminescence in 0D and 3D Semiconducting Copper(I) Iodides

AbstractChiral hybrid Cu(I)‐based iodides with d10 closed shell demonstrate great potential for circularly polarized luminescence (CPL) because of high photoluminescence quantum yield (PLQY). Herein, by incorporating mono‐ or bi‐dentate coordination mode ligands as chiral source, the self‐assembly of four pairs of chiral hybrid Cu(I)‐based iodides, namely, (R/S)‐Cu4I4(Hmpy)4·H2O (R/S‐1), (R/S)‐Cu4I4(3Hpy)4 (R/S‐2), (R/S)‐Cu4I4(2MePI)4 (R/S‐3), and (R/S)‐Cu4I4(3AD)4 (R/S‐4) (where R/S‐Hmpy = R/S‐2‐pyrrolidinemethanol, R/S‐3Hpy = R/S‐3‐hydroxypyrrolidine, R/S‐2MePI = R/S‐2‐methylpiperazine, and R/S‐3AD = R/S‐3‐aminopiperidine), are reported. With the monodentate and bidentate ligands, these materials belong to two different structural types: 0D molecular clusters (R/S‐1, R/S‐2) and 3D porous metal–organic frameworks (R/S‐3, R/S‐4). These materials all crystallize in non‐centrosymmetric space groups containing similar basic Cu4I4 cubane tetramer building units but with different coordination modes. They are also semiconductors, with optical bandgaps ranging from 2.70 to 2.94 eV. The photoluminescence (PL) and circularly polarized luminescence (CPL) emissions are further characterized, where the highest PLQY of ≈95% and CPL dissymmetry factor (glum) of ≈7 × 10−3 are achieved in R/S‐1. This work offers a systematic comparison between different structural types with similar building blocks, bridging by the flexible chiral ligands, and shows that the hybrid copper iodides are highly promising candidates for next‐generation optoelectronics and chiroptics.

YOLO-LWNet: A Lightweight Road Damage Object Detection Network for Mobile Terminal Devices.

To solve the demand for road damage object detection under the resource-constrained conditions of mobile terminal devices, in this paper, we propose the YOLO-LWNet, an efficient lightweight road damage detection algorithm for mobile terminal devices. First, a novel lightweight module, the LWC, is designed and the attention mechanism and activation function are optimized. Then, a lightweight backbone network and an efficient feature fusion network are further proposed with the LWC as the basic building units. Finally, the backbone and feature fusion network in the YOLOv5 is replaced. In this paper, two versions of the YOLO-LWNet, small and tiny, are introduced. The YOLO-LWNet was compared with the YOLOv6 and the YOLOv5 on the RDD-2020 public dataset in various performance aspects. The experimental results show that the YOLO-LWNet outperforms state-of-the-art real-time detectors in terms of balancing detection accuracy, model scale, and computational complexity in the road damage object detection task. It can better achieve the lightweight and accuracy requirements for object detection for mobile terminal devices.

One-Dimensional Chiral Copper Iodide Chain-Like Structure Cu4 I4 (R/S-3-quinuclidinol)3 with Near-Unity Photoluminescence Quantum Yield and Efficient Circularly Polarized Luminescence.

Chiral organic-inorganic hybrid metal halide materials have shown great potential for circularly polarized luminescence (CPL) related applications for their tunable structures and efficient emissions. Here, this work combines the highly emissive Cu4 I4 cubane cluster with chiral organic ligand R/S-3-quinuclidinol, to construct a new type of 1D Cu-I chains, namely Cu4 I4 (R/S-3-quinuclidinol)3 , crystallizing in noncentrosymmetric monoclinic P21 space group. These enantiomorphic hybrids exhibit long-term stability and show bright yellow emission with a photoluminescence quantum yield (PLQY) close to 100%. Due to the successful chirality transfer from the chiral ligands to the inorganic backbone, the enantiomers show intriguing chiroptical properties, such as circular dichroism (CD) and CPL. The CPL dissymmetry factor (glum ) is measured to be ≈4×10-3 . Time-resolved photoluminescence (PL) measurements show long averaged decay lifetime up to 10 µs. The structural details within the Cu4 I4 reveal the chiral nature of these basic building units, which are significantly different than in the achiral case. This discovery provides new structural insights for the design of high performance CPL materials and their applications in light emitting devices.

Alignment of Λ-Shaped Basic Building Units to Construct One New KMoO3(IO3) Polar Polymorph.

Nonlinear optical (NLO) crystals assume an irreplaceable role in the development of laser science and technologies, yet the reasonable design of a high-performance NLO crystal remains difficult owing to the unpredictability of inorganic structures. In this research, we report the fourth polymorph of KMoO3(IO3), i.e., δ-KMoO3(IO3), to understand the effect of different packing patterns of basic building units on structures and properties. Among four polymorphs of KMoO3(IO3), the different stacking patterns of Λ-shaped cis-MoO4(IO3)2 units result in α- and β-KMoO3(IO3) featuring nonpolar layered structures, whereas γ- and δ-KMoO3(IO3) display polar frameworks. Theoretical calculations and structure analysis reveal that IO3 units can be regarded as the main source of its polarization in δ-KMoO3(IO3). Further property measurements show that δ-KMoO3(IO3) exhibits a large second-harmonic generation response (6.6 × KDP), a wide band gap (3.34 eV), and a broad mid-infrared transparency region (∼10 μm), which demonstrates that adjusting the arrangement of the Λ-shaped basic building units is an effective approach for rationally designing NLO crystals.

NaRb6(B4O5(OH)4)3(BO2) Featuring Noncentrosymmetry, Chirality, and the Linear Anionic Group BO2.

Noncentrosymmetric (NCS) structures are of particular interest owing to their symmetry-dependent physical properties, e.g., pyroelectricity, ferroelectricity, piezoelectricity, and nonlinear optical (NLO) behavior. Among them, chiral materials exhibit polarization rotation and host topological properties. Borates often contribute to NCS and chiral structures via their triangular [BO3] and tetrahedral [BO4] units and their numerous superstructure motifs. However, no chiral compound with the linear [BO2] unit has been reported to date. Herein, an NCS and chiral mixed-alkali-metal borate, NaRb6(B4O5(OH)4)3(BO2), with a linear BO2- unit in the structure was synthesized and characterized. The structure features a combination of three types of basic building units (BBUs), [BO2], [BO3], and [BO4] with sp-, sp2-, and sp3-hybridization of boron atoms, respectively. It crystallizes in the trigonal space group R32 (No. 155), one of the 65 Sohncke space groups. Two enantiomers of NaRb6(B4O5(OH)4)3(BO2) were found, and their crystallographic relationships are discussed. These results not only expand the small family of NCS structures with the rare linear BO2- unit but also prompt recognition to the fact that NLO materials have generally overlooked the existence of two enantiomers in achiral Sohncke space groups.

Deep stacked least square support matrix machine with adaptive multi-layer transfer for EEG classification

The recent extraordinary success of deep neural networks for electroencephalogram (EEG) decoding can be mainly attributed to the availability of large-scale labeled datasets. However, it requires prolonged EEG calibration, which is especially inconvenient for people with disabilities. Training deep neural networks with insufficient labeled EEG data will make the model suffer from limited generalization capability. In view of this, a new deep stacked network (DSN), called deep stacked transfer least square support matrix machine (DST-LSSMM), is proposed to alleviate the above issue. Following the philosophy of stacked generalization, the proposed DST-LSSMM utilizes least square support matrix machine (LSSMM) as its basic building unit and the random projection of previous layers as its stacking element. The adopted matrix classifier LSSMM directly models the matrix-form data, which is able to exploit the structural information between the columns or rows in EEG feature matrices to further improve the generalization capability of the model. Besides, we design an adaptive multi-layer model knowledge transfer learning scheme to guarantee consistency across the interrelated layers. The proposed adaptive multi-layer transfer scheme allows the use of model knowledge of previous related layers to facilitate the model construction at higher layers, consequently enhancing the generalization capability of the deep stacked model. DST-LSSMM is carried out in an efficient feed-forward way without parameter pre-training and fine-tuning, which can simplify the model optimization process. We extensively evaluate our method on three EEG datasets. Experimental results demonstrate that our method achieves promising performances on EEG classification.

Uncovering the Early Stages of Magnesium Silicate Hydrate Formation: A Nonclassical Multistep Pathway

Understanding the fundamental physicochemical processes that occur during the hydration of cementitious materials is essential for developing alternative binders that enable the partial substitution of Portland cement (PC), lowering the carbon footprint associated with the cement industry. Magnesium-silicate-hydrate (M-S-H) stands as a potential alternative binder; however, its inferior mechanical properties attributed to its nanostructure, and the high-water demand for curing, hinder the application of MgO-based cement as PC surrogate. A potential strategy to tackle these major drawbacks is based on controlling M-S-H formation from the early stages, building the properties and nanostructure of this binding phase from its basic building units. The present work provides insights into M-S-H nucleation and early growth gathered by combining titration experiments with electrospray ionization mass spectrometry, analytical ultracentrifugation, and transmission electron microscopy. We evidenced a nonclassical multistep pathway where a highly complex mixture of defined hydrated magnesium (sodium)-silicate oligomeric species exists in solution prior nucleation. Our results suggest that these entities aggregate, yielding an ill-defined M-S-H precursor phase (depleted in Mg compared to the final product) which later transforms into a denser M-S-H interconnected network (Mg:Si ratio ca. 1) with a more defined sheet-like structure that still retains its poorly crystalline character. The identification of oligomeric silicates species prior nucleation is of great importance for developing means to regulate M-S-H (and potentially other hydrous silicates) formation by using a bottom-up approach. This work reveals that, during the hydration process of cementitious materials, the stages prior to the formation of hydrated solids cannot be disregarded, as they could open new avenues for engineering the properties of the final materials.

Two metal-free perovskite molecules with different 3D frameworks show reversible phase transition, dielectric anomaly and SHG effect.

Three-dimensional (3D) hybrid organic-inorganic perovskites (HOIPs) have attracted tremendous research interest due to their unique structure and promising applications. However, research on the design, synthesis and properties of this kind of metal-free crystalline material is still in the exploratory stage. Herein, two 3D perovskite molecules [1,4-3.2.2-dabcn]NH4Br3 (1) and [1,4-3.2.2-dabcn]NH4I3·0.5H2O (2) were obtained by reacting 1,4-diazabicyclo[3.2.2]nonane (1,4-3.2.2-dabcn) with NH4X (X = Br and I) in the corresponding concentrated halogen acids. The single X-ray diffraction results demonstrated that the inorganic framework structures in compounds 1 and 2 constructed with NH4Br and NH4I are completely different, caused by the radius of the bromide ion being smaller than that of the iodide ion. The 3D framework of compound 1 is constructed with a coplanar dimer [(NH4)2Br6]2- as the basic building unit, leading to the expanded 3D perovskite framework structure with a larger cavity to accommodate the 1,4-3.2.2-dabcn molecule. Nevertheless, compound 2 adopts a familiar 3D crystal framework structure with corner-sharing [(NH4)I6] octahedra, where the [1,4-3.2.2-dabcn] cations and water solvent molecule are confined in the cavities enclosed by the octahedra. Notably, both compounds exhibit reversible phase transition, dielectric anomaly and the second harmonic generation (SHG) effect. From the perspective of molecular design, this work is of great significance to guide the construction of new 3D metal-free perovskite molecular materials with reversible properties.