Treatment of [Cu(MeCN)₄][BF₄] with 2,9-dimethyl-1,10-phenanthroline (dmp) and either pyrazine (pyz), 4,4′-bipyridine (4,4′-bipy) or trans-1,2-bis(pyridin-4-yl)ethene (bpe) gave, depending on conditions, the copper(I) species [{Cu(dmp)(NCMe)}₂(µ-diimine)]²⁺, {[Cu(dmp)(µ-diimine)]_n}ⁿ⁺ (diimine = 4,4′-bipy or bpe) or [Cu(dmp)₂]BF₄·xsolv (x = 0.5, solv = CH₂Cl₂; x = 1, solv = C₇H₈). The discrete dinuclear cation [{Cu(dmp)(NCMe)}₂(µ-4,4′-bipy)]²⁺ comprises two distorted tetrahedral copper(I) centres (Cu· · ·Cu 11.23 Å), each ligated by a bidentate dmp ligand (mean Cu–N 2.059 Å), an acetonitrile molecule (Cu–N 1.943 Å), and bridged by a 4,4′-bipyridine molecule (Cu–N 2.070 Å). The polymeric species {[Cu(dmp)(µ-diimine)]_n}ⁿ⁺ both comprise 1-D polymeric zig-zag chains, based on distorted tetrahedral copper(I) co-ordination geometries, each copper atom being ligated by the dmp ligand and two pyridine N-atoms [diimine = 4,4′-bipy: Cu· · ·Cu 11.11, mean Cu–N (dmp) 2.073, mean Cu–N (py) 2.011 Å; diimine = bpe: mean Cu· · ·Cu 13.375, mean Cu–N (dmp) 2.061, mean Cu–N (py) 1.996 Å]. π–π Stacking interactions between dmp molecules in the 4,4′-bipy bridged polymer leads to the formation of large elliptical channels which host two chains of alternating tetrafluoroborate anions and acetonitrile solvent molecules. The mononuclear species [Cu(dmp)₂]BF₄·xsolv (x = 0.5, solv = CH₂Cl₂; x = 1 solv = C₇H₈) are also based on tetrahedral copper(I); that in [Cu(dmp)₂]BF₄·0.5CH₂Cl₂ is highly distorted with three short (2.006–2.074 Å) and one longer Cu–N distance (2.139 Å), that in [Cu(dmp)₂]BF₄·C₇H₈ is much more regular with four similar Cu–N distances (2.022–2.025 Å).