{
  "abstract": "Birefringent crystals are indispensable for optoelectronic applications, yet commercially available crystals still suffer from the drawback of insufficient birefringence. Meanwhile, tetracoordination units—traditionally confined to a tetrahedral geometry—have long been sidelined from mainstream high-performance birefringent materials due to their intrinsic nearly negligible polarizability anisotropy. Herein, we break this tetrahedral constraint—demonstrating tetracoordinate square-planar [ICl 4 ] anions as a revolutionary platform for unprecedented birefringence. To achieve this, we report an improved synthesis method that avoids the use of toxic Cl 2 gas, enabling the preparation of [C(NH 2 ) 3 ][ICl 4 ] featuring square-planar [ICl 4 ] units. This compound displays a birefringence of 0.975@550 nm, setting a new record that surpasses all existing compounds containing tetracoordinate structural units. The giant birefringence of this material is attributed to the strong polarization anisotropy induced by the unique square-planar geometry of the [ICl 4 ] tetracoordinate units. This research provides theoretical guidance for designing high-performance polar materials based on tetracoordinate units in giant birefringent materials and promotes applications in related optoelectronic device.",
  "abstract_shown": true,
  "affiliations": [
    "College of Chemistry and Materials, Jiangxi Normal University, Nanchang, Jiangxi, 330022, P. R. China.",
    "State Key Laboratory of Functional Crystals and Devices, Chinese Academy of Sciences Fujian Institute of Research on the Structure of Matter, Fuzhou, Fujian, 350002, P. R. China.",
    "Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area, Shenzhen, Guangdong, 518000, P. R. China."
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 8,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Zhiwei Sun",
      "orcid": "0009-0004-3282-6963"
    },
    {
      "affs": [
        0
      ],
      "name": "Qingran Ding",
      "orcid": "0000-0003-0725-7688"
    },
    {
      "affs": [
        1
      ],
      "name": "Weiqi Huang",
      "orcid": "0000-0002-7231-6632"
    },
    {
      "affs": [
        0
      ],
      "name": "Peixuan Zhu",
      "orcid": "0009-0007-7825-2143"
    },
    {
      "affs": [
        0
      ],
      "name": "Guimei Lai",
      "orcid": "0009-0009-5222-5010"
    },
    {
      "affs": [
        0
      ],
      "name": "Xue Mei"
    },
    {
      "affs": [
        2
      ],
      "name": "Sangen Zhao",
      "orcid": "0000-0002-1190-684X"
    },
    {
      "affs": [
        0,
        1
      ],
      "name": "Junhua Luo",
      "orcid": "0009-0002-0470-3902"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ckmadyq0n4t06.bib",
  "cited_by": 0,
  "doi": "10.1126/sciadv.aef7948",
  "fulltext_url": null,
  "id": "ckmadyq0n4t06",
  "issns": [
    "2375-2548"
  ],
  "landing_url": "https://www.science.org/doi/10.1126/sciadv.aef7948",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2504|Crystal Structures and Properties"
    ]
  ],
  "openalex": "W7222493039",
  "pdf_url": "https://www.science.org/doi/pdf/10.1126/sciadv.aef7948?download=true",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-16",
  "publisher": "American Association for the Advancement of Science (AAAS)",
  "ris": "https://research.draconitic.com/paper/ckmadyq0n4t06.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:41Z",
      "native_id": "10.1126/sciadv.aef7948",
      "source": "crossref",
      "url": "https://www.science.org/doi/10.1126/sciadv.aef7948"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "openalex:2504|Crystal Structures and Properties",
      "subfield": "materials-polymers"
    }
  ],
  "title": "Breaking the tetrahedral constraint of tetracoordination: Square-planar [ICl ₄ ] enables unprecedented birefringence in [C(NH ₂ ) ₃ ][ICl ₄ ]",
  "title_text": "Breaking the tetrahedral constraint of tetracoordination: Square-planar [ICl ₄ ] enables unprecedented birefringence in [C(NH ₂ ) ₃ ][ICl ₄ ]",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:17:41Z",
  "url": "https://research.draconitic.com/paper/ckmadyq0n4t06",
  "venue": "Science Advances",
  "versions": []
}