Electrically conductive 1D coordination polymers: design strategies and controlling factors

Frames 1D CPs as emerging electrical conductors and links structural component selection to electronic-device applications.

Relevance: Core · 29 · Abstract

Concludes that 1D CPs mainly show semiconductor-region conductivity and that stronger experimental and theoretical understanding is still needed.

Relevance: Core · 36 · Conclusions and outlook

Treats solid-state photochemical cycloaddition as a post-synthetic structural modification that can either increase or decrease conductivity through changes to pi contacts and metal-centre distances.

Relevance: Core · 33 · Effect of [2 + 2] cycloaddition of CPs · Scheme 2

Lists the review's controlling-factor framework: metal ions, ligand substituents, photochemical cycloaddition, non-covalent interactions, flexibility, linking atoms, linker conjugation and guests.

Relevance: Core · 31 · Design strategies

Connects coordination-network flexibility, softer linking atoms and extended pi conjugation to band dispersion, lower transport barriers and charge hopping pathways.

Relevance: Core · 35 · Effects of size and conjugation of the linkers · Fig. 6

Describes guest molecules as conductivity modulators through redox activity, ordered guest alignment, ionic motion, charge transfer and donor-acceptor stack formation.

Relevance: Core · 36 · Guest-induced electrical conductivity

Introduces CPs and MOFs as polymeric coordination materials, identifies low intrinsic conductivity as a common issue, and positions 1D CPs as a tractable structure-property platform.

Relevance: Core · 30 · Introduction

Summarises measurement complications, sample-dependence, device geometries and common I-V methods without attempting a full metrology guide.

Relevance: Core · 31 · Measurement methods · Scheme 1

Explains how metal size, d-orbital occupancy and metal-ligand orbital overlap influence long-range charge movement.

Relevance: Core · 31 · Effect of metal ions · Fig. 1

Defines through-space charge transport as mediated by pi-pi, C-H...pi and hydrogen-bond interactions and contrasts it with through-bond transport.

Relevance: Core · 34 · Effect of non-covalent interactions

Uses para-functionalised aromatic ligands to show how substituents tune interplanar distances and halogen/pi interactions.

Relevance: Core · 32 · Effect of para-substituents of ligands · Fig. 2

Conductivity-controlling design factors

This is the article's central organising framework for explaining how 1D CP conductivity is tuned.

Categories: metal-ion size and nature · para-substituents of ligands · [2 + 2] cycloaddition · non-covalent interactions · structural flexibility · linking atoms · linker conjugation · guest molecules

31 · Design strategies

Guest-induced conductivity mechanisms

Guest molecules are classified by the review into several mechanisms for changing conduction in CP networks.

Categories: redox activation of guests · ordered guest alignment · ionic guest motion · metal-to-ligand charge transfer · intercalated pi donor-acceptor stacks

36 · Guest-induced electrical conductivity

Conductivity measurement modes

The measurement section distinguishes intrinsic material measurements from device-based values and names common I-V geometries.

Categories: direct material conductivity · device-fabrication measurements · two-probe I-V · four-probe I-V · van der Pauw

31 · Measurement methods

Review scope: ligand-based 1D CPs versus Q1D metal chains

The review uses Q1D chains as historical context but excludes detailed treatment of MX/MMX, proton and ion conductors from its main design-strategy discussion.

Categories: 1D CPs where metal nodes and organic ligands both contribute to charge transport · Q1D MX and MMX halogen-bridged metal chains · proton- or ion-conducting CPs

30 · Introduction

Through-bond versus through-space charge transport

The review treats through-bond and through-space routes as the main mechanistic approaches, with hopping and band transport as underlying descriptions.

Categories: through-bond transport · through-space transport · hopping · band transport

34 · Effect of non-covalent interactions

Chain-like coordination arrays in which metal nodes are connected by organic ligands and conductivity is interpreted through structure-property relationships.

Conduction: Usually semiconductor-region conductivity, controlled by orbital overlap, non-covalent contacts and structural modifications.

Representative materials: [Cd(adc)(4-phpy)2(H2O)2] · [Zn(cis-1,4-chdc)(4-phpy)]n · [Zn4(adc)4(4-cltpy)4].CH3OH.2H2O

Nodes / linkers: Cd(II) · Zn(II) · Cu(II) · Co(II) · dicarboxylates · pyridyl ligands · organosulfur ligands

30 · Introduction

CPs or related coordination frameworks whose conductivity is changed by guest molecules such as iodine.

Conduction: Guest-induced redox chemistry, intercalation and donor-acceptor stacking can shift materials from insulating to semiconducting or much more conductive states.

Representative materials: Cu[Ni(pdt)2] · Co3(NDC)3 · [Fe(pc)(mu-pyz)]

Nodes / linkers: Cu/Ni · Co · Fe · pyrazinedithiolate · naphthalenedicarboxylate · phthalocyaninato-pyrazine stacks

36 · Guest-induced electrical conductivity

Structurally related Cd/Zn or other metal variants used to isolate how cation size and metal-ligand overlap affect conductivity.

Conduction: Larger cations are associated with better orbital overlap, shorter contacts and improved conductivity in the review examples.

Representative materials: [Cd(adc)(4-phpy)2(H2O)2] · [Zn(adc)(4-phpy)2(H2O)2] · {[Cd(adc)(4-spy)2(H2O)2]}n

Nodes / linkers: Cd(II) · Zn(II) · acetylenedicarboxylate · 4-phenylpyridine · 4-styrylpyridine

32 · Effect of metal ions · Fig. 1

1D CPs using softer sulphur-containing linkers or bridging atoms to reduce band gaps and improve band dispersion.

Conduction: Soft linking atoms are interpreted as lowering band gaps and enabling metal-organothiolate pathways.

Representative materials: [Co(C9H6NS)2] · aromatic organothiolate CPs

Nodes / linkers: Co(II) · transition metals · 8-mercaptoquinoline · organothiolates · sulfur bridges

35 · Effect of linking atoms

1D CPs where para-functionalised pyridyl or benzoate ligands tune pi, C-H...pi and halogen...pi interactions.

Conduction: Conductivity is attributed to substituent-driven changes in supramolecular interactions and interlayer distance.

Representative materials: [Cd(nip)(4-clpy)(CH3OH)] · [Cd(nip)(4-brpy)(CH3OH)] · [Cd(nip)(4-phpy)(H2O)].DMF.3H2O · [Co(adc)(4-ppy)(H2O)2]n

Nodes / linkers: Cd(II) · Co(II) · nitroisophthalate · chloropyridine · bromopyridine · phenylpyridine · bromophenylpyridine

32 · Effect of para-substituents of ligands · Fig. 2

Coordination polymers containing suitably oriented alkene ligands that undergo light-induced cycloaddition and structural transformation.

Conduction: Conductivity can increase or decrease depending on whether cycloaddition strengthens or weakens pi stacking and metal-centre proximity.

Representative materials: [Ag2(4-stilbz)4][CF3SO3]2 · [Cd(quin)2(4-nvp)] · [Cd(adc)(4-nvp)2(H2O)]n

Nodes / linkers: Ag(I) · Cd(II) · stilbazole · naphthylvinylpyridine · alkene-containing N-donor ligands

33 · Effect of [2 + 2] cycloaddition of CPs · Scheme 2

Transition-metal halide chain compounds used as historical conductive comparators rather than the review's core class.

Conduction: Conductivity is linked to metal-halogen orbital overlap and direct metal-metal overlap, with iodine-containing chains favoured over bromide and chloride analogues.

Representative materials: MX chain compounds · MMX chain compounds

Nodes / linkers: transition metals · halide bridges

30 · Introduction

Introduce redox-active or ordered guests

Use guest molecules to oxidise/reduce frameworks, align charge carriers or intercalate donor-acceptor stacks.

Claimed effects: Guest inclusion can transform insulating frameworks into semiconductors or dramatically raise conductivity in stacked macrocyclic systems.

Controlling variables: guest redox activity · guest alignment · iodine loading · framework oxidation

Representative materials: Cu[Ni(pdt)2] · Co3(NDC)3 · [Fe(pc)(mu-pyz)]

Caveat: Guest-induced values are extrinsic and should be separated from pristine-framework conductivity in Chapter 1 comparisons.

36 · Guest-induced electrical conductivity

Increase linker pi conjugation

Choose extended dicarboxylate or N-donor ligands to reduce HOMO-LUMO gaps and increase electronic communication.

Claimed effects: Greater conjugation can improve charge hopping through space and generate strong photosensitivity in optoelectronic candidates.

Controlling variables: pi-electron conjugation length · N-donor ligand surface area · adjacent-layer pi interactions

Representative materials: [Zn4(adc)4(4-cltpy)4].CH3OH.2H2O

Caveat: Conjugation is presented alongside packing and non-covalent contacts, not as a sole predictor.

35 · Effects of size and conjugation of the linkers · Fig. 6

Use softer linking atoms

Replace hard oxygen-rich connections with softer sulphur or selenium-containing centres where appropriate.

Claimed effects: Softer linking atoms are interpreted as reducing band gaps, enhancing band dispersion and lowering the energy barrier for charge transport.

Controlling variables: linking atom electronegativity · S or Se donor identity · metal-organothiolate pathway · band dispersion

Representative materials: [Co(C9H6NS)2]

Caveat: The review describes sulphur/selenium linkers as less common, so this strategy has fewer examples than oxygen-carboxylate CPs.

35 · Effect of linking atoms

Select metal ions for favourable orbital overlap

Use metal size, coordination preferences and d-orbital occupancy to tune metal-ligand overlap and the supramolecular geometry of 1D chains.

Claimed effects: Improved overlap and shorter contacts are associated with enhanced charge movement and higher conductivity in Cd/Zn and Cu examples.

Controlling variables: cation size · d-orbital occupancy · coordination geometry · metal-ligand orbital overlap

Representative materials: [Cd(adc)(4-phpy)2(H2O)2] · [Zn(adc)(4-phpy)2(H2O)2] · [Cu(fum)(4-phpy)2(H2O)]

Caveat: The review gives design interpretation rather than a universal metal-series rule; primary studies remain needed for quantitative comparison.

31 · Effect of metal ions

Engineer through-space non-covalent pathways

Use pi-pi, C-H...pi, hydrogen-bonding and related contacts to create charge-hopping pathways between chains or layers.

Claimed effects: Through-space interactions are presented as key for charge transport when direct covalent conjugation is limited.

Controlling variables: pi-pi stacking distance · C-H...pi contacts · hydrogen-bond networks · chain packing

Representative materials: [Zn(cis-1,4-chdc)(4-phpy)]n · [CuX(ANP)]n · [Pd(dabdOH)Br]Br2

Caveat: The review does not provide a unified quantitative model for the relative contributions of individual non-covalent contacts.

34 · Effect of non-covalent interactions

Tune para-substituted aromatic ligands

Use para-substituents on monodentate aromatic ligands or benzoates to alter supramolecular contacts and interplanar distances.

Claimed effects: Appropriate substituents can strengthen through-space pathways and shift conductivity across related 1D CPs.

Controlling variables: para substituent identity · pi-pi stacking · halogen-pi interactions · interlayer distance

Representative materials: [Cd(nip)(4-phpy)(H2O)].DMF.3H2O · [Cd(nip)(4-brpy)(CH3OH)] · [Co(adc)(4-ppy)(H2O)2]n

Caveat: Substituent effects are mediated by packing and non-covalent contacts, so the same substituent logic may not transfer directly across frameworks.

32 · Effect of para-substituents of ligands

Use solid-state [2 + 2] photochemical cycloaddition

Design olefinic ligands to satisfy topochemical alignment and transform CP structures under light irradiation.

Claimed effects: Photocycloaddition can tune conductivity by changing pi contacts and metal-centre separations.

Controlling variables: C=C orientation · UV irradiation · metal-centre distance · pi-pi contact strength

Representative materials: [Ag2(4-stilbz)4][CF3SO3]2 · [Cd(quin)2(4-nvp)] · [Cd(adc)(4-nvp)2(H2O)]n

Caveat: The direction of conductivity change depends on the structural consequence of cycloaddition; the review reports both increases and decreases.

33 · Effect of [2 + 2] cycloaddition of CPs

Exploit structural flexibility

Choose metal ions and ligands that permit dynamic chain distortions or flexible one-dimensional motifs.

Claimed effects: Flexible CuI chains and S-S-bonded zigzag chains can show large conductivity changes in response to temperature, sorption or illumination.

Controlling variables: ligand length · ligand functionality · reaction conditions · sorption-induced distortion

Representative materials: CuI-ANP polymorphs · [Cd(2,2'-dsb)(4-nvp)(DMF)(H2O)]

Caveat: Flexibility is useful only when the distortion improves charge-transfer pathways; uncontrolled distortion could also disrupt contacts.

34 · Effect of the structural flexibility of CPs

The review expects the discussed strategies to improve future design principles but does not claim a predictive framework is already complete.

Proposed direction: Develop comparative series that isolate metal, linker, packing and guest effects to convert qualitative design rules into predictive models.

36 · Conclusions and outlook

The review frames conductive CPs as promising for lab-to-land electronic and optoelectronic devices, but many cited examples remain material or I-V studies.

Proposed direction: Bridge from isolated conductivity and Schottky behaviour to reproducible thin-film device metrics for LED, FET, SBD and photovoltaic contexts.

36 · Conclusions and outlook

The review emphasises that conductivity measurements depend on sample form, device components and the I-V range.

Proposed direction: Report voltage/current windows, sample morphology, contacts and device geometry consistently when comparing 1D CP conductivities.

31 · Measurement methods

The review states that understanding of conductivity in CPs remains deficient in most cases.

Proposed direction: Combine significant experimental and theoretical work to resolve transport mechanisms rather than relying only on structural correlations.

36 · Conclusions and outlook

The review repeatedly invokes pi-pi, C-H...pi and hydrogen-bond contacts but does not quantify their separate transport contributions.

Proposed direction: Use paired structural/electronic studies to separate through-space contact effects from through-bond orbital overlap.

34 · Effect of non-covalent interactions